1D engine simulation

1D-3D CFD coupling connects one-dimensional engine or system simulation with three-dimensional CFD simulation. Typically, 1D models provide boundary conditions for 3D CFD, while 3D CFD returns discharge coefficients, pressure losses, heat transfer data or characteristic values. This allows system behaviour and local component physics to be evaluated consistently. This coupling is especially valuable for intake systems, exhaust manifolds, turbocharger surroundings, in-cylinder flow and cooling.

1D-3D coupling describes the connection between 1D system simulation and 3D CFD. The 1D simulation provides fast system boundary conditions such as mass flow rates, pressures, temperatures or time histories. The 3D CFD provides local information on flow, pressure loss, heat transfer, mixing or component behaviour. Good coupling uses both modelling levels deliberately without turning every question into an expensive co-simulation.

1D-3D coupling connects the fast system level of 1D simulation with the local detail resolution of 3D CFD. The 1D simulation provides realistic boundary conditions such as time-dependent pressures, temperatures, mass flow rates or species fractions. The 3D CFD then calculates local flow, mixing, heat transfer, pressure loss or component loading. Standalone 3D CFD considers only the selected computational domain and therefore requires suitable boundary conditions from outside. If these boundary conditions are oversimplified, even a very detailed 3D CFD simulation can produce incorrect engineering conclusions. 1D-3D coupling is especially useful for pulsating engine flows, turbocharger surroundings, intake systems, exhaust manifolds, in-cylinder flow and cooling. Standalone 3D CFD is useful when the system environment is simple or boundary conditions are reliably known. In complex engine projects, coupling is often more robust because it combines system behaviour and local physics consistently.

1D simulation is a simulation method in which physical processes are described along one main flow direction. In engine development, this usually means that pipes, ducts, plenums, valves, turbochargers and cylinders are modelled as connected system elements. The method is very well suited for evaluating complete systems and operating strategies quickly. Its limitation appears when local three-dimensional effects such as vortices, flow separation or mixture inhomogeneity become decisive.

1D simulation represents a system using pipes, volumes, components and maps. It is especially suited for air paths, exhaust paths, gas exchange, boosting, cooling circuits, drive cycles and many operating points. 3D CFD, by contrast, calculates local flow fields in real geometry. It can resolve vortices, separation, pressure losses, temperature fields, mixing and wall heat transfer in space. 1D simulation is fast and system-oriented, while 3D CFD is more detailed and computationally expensive. In engine development, 1D simulation often provides boundary conditions for 3D CFD. Conversely, 3D CFD can generate discharge coefficients, pressure losses or heat transfer data for 1D models. The best approach is often to combine both methods rather than choosing only one simulation level.

1D turbo matching uses compressor maps, turbine maps, engine models and operating limits to select a suitable turbocharger computationally. Many variants can be evaluated quickly over engine speed, load, boost pressure, surge margin, exhaust temperature and efficiency. The advantage is speed, variant capability and early availability in the development process. Test bench turbo matching measures real behaviour on the engine with actual hardware. This reveals effects that are only simplified in simulation, such as heat losses, leakage, actuator behaviour, manufacturing scatter and real pulsations. The test bench is more reliable, but more expensive, slower and hardware-dependent. 1D matching reduces the number of required hardware variants and makes test bench work more targeted. The clean development logic is: preselection and optimization in 1D, validation and fine tuning on the test bench.

Air path simulation describes the calculation of the intake system from air inlet to cylinder. It includes air filter, airbox, throttle valve, compressor, charge air cooler, intake manifold, intake ports and valves. Important results include air mass flow, pressure loss, boost pressure, temperature, cylinder filling and dynamics during load changes. Air path simulation is decisive for drivability, power, fuel consumption and boosting strategy.

Aftertreatment simulation calculates the behaviour of catalysts, particulate filters, SCR systems and sensors in the exhaust system. It considers temperature history, mass flow rates, pollutant conversion, storage behaviour, regeneration and control strategy. It is especially important for cold start, warm-up, real-world emissions and coupled engine-aftertreatment calibration. In 1D environments, it can be directly linked to engine operation, exhaust gas temperature and exhaust mass flow.

Boosting system simulation calculates the behaviour of turbochargers, superchargers, charge air coolers, wastegates, VGT systems and bypass paths. The goal is to evaluate boost pressure, air mass flow, turbocharger speed, efficiency and transient response across the engine map. It is a central tool for turbo matching and downsizing concepts. Especially in hydrogen and high-performance engines, boosting is closely linked to excess air, knock limit, NOx and component protection.

Boost pressure is the pressure of the compressed intake air downstream of the compressor or in the intake system. It increases the air mass in the cylinder and therefore the possible torque and power. Excessive boost pressure can cause knock, high exhaust temperatures, mechanical loading or turbocharger limit issues. In 1D engine simulation, boost pressure is a central quantity for turbo matching, full load and transient response.

Boost pressure control describes regulation of the desired boost pressure using wastegate, VGT, bypass, throttling or electric assistance. The goal is fast, stable and safe boost build-up. The control must consider turbocharger speed, surge limit, exhaust temperature, knock limit and torque demand. In 1D engine simulations, it is used to represent transient behaviour and operating limits realistically.

Boundary conditions for 3D CFD define how the computational domain is connected to its environment. In engine projects, they can come from 1D simulations, for example time-dependent pressures, temperatures, mass flow rates or species fractions. Good boundary conditions are crucial because they strongly influence the local 3D result. Especially for pulsating intake and exhaust flows, realistic transient boundary conditions are often more important than extremely detailed local modelling.

Brake efficiency describes what fraction of the fuel energy is available as usable power at the crankshaft. It includes thermodynamic losses, friction, pumping losses and auxiliaries. It is especially important for real applications because it describes the actually usable engine efficiency. In 1D simulation, it is used to compare fuel consumption, engine maps and concept variants directly.

Brake mean effective pressure describes the usable engine work available at the crankshaft relative to displacement. It includes mechanical losses and is therefore directly related to torque and usable engine power. BMEP is a central metric for power density and engine design. High BMEP values place increased demands on boosting, combustion, cooling, mechanics and durability.

Brake-specific fuel consumption describes fuel mass flow relative to brake power output. It is commonly given in grams per kilowatt-hour and allows comparison between different engine sizes. Low BSFC means high brake efficiency. In 1D engine simulation, BSFC is an important map quantity for fuel consumption optimization, operating point selection and concept comparison.

Brake-specific hydrogen consumption describes hydrogen mass flow relative to brake power output. It is the hydrogen equivalent of brake-specific fuel consumption and is often considered in grams per kilowatt-hour. The quantity is useful for comparing operating points, combustion concepts and engine variants. For hydrogen, tank and storage effects should also be considered because mass and volume have very different implications.

A charge air cooler model describes the cooling of compressed intake air downstream of the compressor. It calculates temperature change, pressure loss, heat transfer and, where relevant, thermal inertia. Cooling the charge air increases density and can reduce knock tendency and component temperatures. In 1D engine simulation, the model is important for power prediction, boost control, thermal management and transient behaviour.

The choke line describes the region in a compressor or turbine map where mass flow hardly increases despite increasing pressure difference. It is caused by very high local flow velocities and limited flow capacity. In a compressor, it limits the maximum possible air mass flow at high loads and engine speeds. In engine simulation, the choke line indicates whether the selected turbocharger provides enough flow capacity for the power target.

Combustion duration describes the crank angle or time interval over which the main portion of the fuel burns. It is often defined using mass fraction burned points such as MFB10 to MFB90. Short combustion duration can improve efficiency, but may increase pressure rise rate and knock tendency. Long combustion duration can reduce efficiency and stability and increase exhaust gas temperature.

A combustion model describes the conversion of fuel in the cylinder over time or crank angle. It can be empirical, semi-empirical or predictive. Simple models use prescribed functions such as the Wiebe function, while predictive models respond more strongly to turbulence, flame speed and mixture state. The combustion model is decisive for cylinder pressure, efficiency, exhaust gas temperature and knock assessment.

Combustion phasing describes the position of combustion relative to top dead centre. MFB50 is often used, meaning the crank angle at which 50 percent of the fuel mass has burned. Optimal combustion phasing is decisive for efficiency, torque, exhaust gas temperature, knock and component loading. In 1D engine simulation, combustion phasing is a central target quantity for spark timing, combustion modelling and calibration.

The combustion profile describes how combustion progresses over crank angle or time. It shows when combustion starts, how quickly fuel energy is converted and when combustion is completed. In 1D engine simulation, the combustion profile is often used as an input, calibration quantity or result of a combustion model. It affects cylinder pressure, efficiency, exhaust gas temperature, pressure rise rate and knock tendency.

The combustion profile describes what fraction of the fuel mass has already burned over crank angle or time. Typical values are MFB10, MFB50 and MFB90. The heat release rate, by contrast, describes the rate of heat release during combustion. It therefore shows not only how far combustion has progressed, but how intensively heat is released at a given point. The combustion profile is a cumulative quantity, while heat release rate is a rate. Both quantities are often calculated from the cylinder pressure trace. The combustion profile is useful for describing start of combustion, combustion phasing and combustion duration. The heat release rate shows in more detail whether heat release is fast, multi-stage, delayed or unstable. For 1D engine simulation, combustion analysis and model calibration, both quantities are needed together.

A CO model describes carbon monoxide formation and oxidation during combustion. CO is formed when carbon in the fuel is not fully converted to CO2. Influencing factors include lambda, temperature, local mixture distribution, near-wall regions, residence time and incomplete combustion. In 1D engine simulation, a CO model is especially relevant for spark-ignition engines, cold start, rich operation and aftertreatment.

The compressor map describes the behaviour of a turbocharger compressor in terms of mass flow, pressure ratio, speed and efficiency. It also shows operating limits such as surge line and choke line. In 1D engine simulation, it is used to calculate compressor operation across the engine map. A correct compressor map is decisive for boost pressure, efficiency, charge air temperature and surge margin.

The compressor map describes the compressor side of a turbocharger. It shows mass flow, pressure ratio, speed, efficiency as well as surge and choke limits. The turbine map describes the exhaust side of the turbocharger. It shows how exhaust mass flow, pressure ratio, speed and efficiency are converted into shaft power. For turbo matching, both maps must be considered together. Good compressor operation is of limited value if the turbine creates too much exhaust back pressure or provides too little power. A well-matched turbine can also drive the compressor into unfavourable regions such as near surge or overspeed. In 1D engine simulation, the combination of both maps determines boost build-up, fuel consumption, exhaust temperature, response and operating safety.

Compressor outlet temperature is the air temperature directly downstream of the compressor. It increases due to compression and depends strongly on pressure ratio and compressor efficiency. High compressor outlet temperatures reduce air density and can increase knock tendency, component temperatures and charge air cooling demand. In 1D engine simulation, it is important for charge air cooler design, turbo matching and thermal assessment.

Computation time describes the time a simulation model requires to complete a calculation. In 1D engine simulation, it is usually much shorter than in 3D CFD, enabling many operating points and variants. Computation time depends on model size, time step, physical models, transients, convergence and hardware. A good modelling strategy balances computation time and result quality instead of always using the most detailed model.

Cooling circuit simulation describes the system-level calculation of coolant circuits, pumps, thermostats, radiators, heat exchangers and thermal masses. It is used to evaluate temperatures, volume flow rates, pressure losses and warm-up behaviour in an engine cooling system. In 1D simulation, many operating states and control strategies can be investigated efficiently. For local hot spots or detailed component temperatures, it is often supplemented by 3D CFD or thermal FEA.

Co-simulation means that two or more simulation models run simultaneously and exchange data during the calculation. Examples include coupling between 1D engine simulation, control model, thermal management model or 3D CFD. It is useful when the interaction between models is time-dependent and strongly coupled. Co-simulation is more complex than simple data exchange and should only be used when the additional benefit justifies the complexity.

Cylinder pressure is the pressure in the combustion chamber during one engine cycle. In 1D engine simulation, it is a central result quantity for combustion, indicated work, pressure rise rate, peak cylinder pressure and efficiency. Combustion profile, heat release rate and mean effective pressures can be derived from cylinder pressure. Correlation with measured cylinder pressure data is one of the most important steps in validating an engine cycle model.

Data-based calibration adjusts model parameters so that the simulation model reproduces available test bench or vehicle data as well as possible. It is very important for representing real engines reliably and reducing model errors. The disadvantage is that prediction quality strongly depends on the amount, quality and coverage of the measurement data. Predictive simulation attempts to forecast results more strongly from physical models and input variables. It is especially valuable when new concepts, new fuels or variants without measurement data need to be evaluated. However, the models are more complex and still require validation. Calibrated models are strong in known operating ranges, while predictive models are more useful for extrapolation and concept decisions. In practice, the best solution is usually a combination: physically meaningful models calibrated and validated with high-quality measurement data.

The discharge coefficient describes how strongly a real flow deviates from the ideal possible flow. It accounts for losses due to geometry, contraction, friction, separation and local flow effects. In 1D engine simulation, it is often used for valves, throttles, orifices and ports. A correct discharge coefficient is important for mass flow, filling, pressure loss and gas exchange.

Drive cycle simulation calculates engine operation over a defined driving cycle with changing vehicle speeds, loads and operating states. It is used to evaluate fuel consumption, emissions, temperatures, battery load, hybrid strategy and aftertreatment over a realistic time history. In 1D engine simulation, engine, air path, thermal management and aftertreatment can be considered together. This reveals effects that are not visible in individual steady-state operating points.

Operating point simulation calculates individual defined operating points with fixed engine speed, load and boundary conditions. It is fast, transparent and well suited for maps, calibration and variant comparisons. Drive cycle simulation, by contrast, calculates a time-dependent sequence with changing speed, load, temperatures and control variables. This reveals warm-up, load changes, turbocharger dynamics, aftertreatment and thermal storage effects. An operating point can describe a stable state very accurately, but says little about transitions between states. A drive cycle shows more realistic operating behaviour, but is more demanding and requires more model information. For fuel consumption and emissions assessment, drive cycles are often more meaningful. For root cause analysis, model calibration and quick concept comparisons, operating point simulations remain indispensable.

Effective flow area describes the effective area through which a fluid flows when real losses are considered. It is often smaller than the geometric opening area. In valve, throttle and component models, it links geometry with flow behaviour. In 1D engine simulations, this quantity is important for representing real components correctly with simplified models.

Efficiency generally describes the ratio of useful output power or work to supplied energy. In engine development, thermal, indicated, brake and mechanical efficiency are distinguished. This distinction is important because losses from combustion, wall heat transfer, exhaust energy, friction and gas exchange occur at different stages. In 1D engine simulation, efficiency quantities help analyse loss chains and identify optimization potential.

The EGR rate describes the fraction of recirculated exhaust gas in the fresh intake charge. It is an important control variable for reducing combustion temperature and NOx emissions. At the same time, it affects ignition behaviour, burn duration, knock tendency, air mass flow and turbocharger operation. In 1D engine simulations, EGR rate is often varied to evaluate emissions, efficiency and operating strategy.

An emissions model calculates or estimates pollutant formation in the engine or conversion in the aftertreatment system. In 1D engine simulations, emissions models are often used for NOx, soot, CO and HC. The models strongly depend on temperature, lambda, pressure, residence time, mixture formation and combustion profile. For reliable results, emissions models must be correlated with test data, 3D CFD or suitable reference cases.

An engine cycle model describes the repeating working cycle of an engine over crank angle or time. It calculates state variables such as pressure, temperature, mass and energy in the cylinder and adjacent systems. This enables analysis of combustion profile, gas exchange, indicated work and efficiency. An engine cycle model is the basis for consistently evaluating individual operating points or complete engine maps.

Engine cycle simulation describes the calculation of the thermodynamic working process of an engine over intake, compression, combustion, expansion and exhaust. It considers cylinder pressure, temperature, combustion profile, heat transfer, gas exchange and efficiency. The focus is to understand the engine cycle and its effects on power, fuel consumption and emissions. In 1D tools such as GT-Power, engine cycle simulation is closely coupled with air path, exhaust path and component models.

Engine cycle simulation calculates the thermodynamic working process of an engine over crank angle or time. It considers cylinder pressure, temperature, combustion profile, heat release rate, gas exchange, efficiency and mean effective pressures. 3D CFD, by contrast, calculates local flow and, where required, combustion in a three-dimensional geometry. Engine cycle simulation is ideal for evaluating many operating points, maps, spark timings, compression ratios or turbocharger concepts quickly. 3D CFD is better when local causes matter, such as mixture inhomogeneity, spray pattern, flame propagation, valve flow or in-cylinder turbulence. Engine cycle simulation requires simplified models for heat transfer, combustion and flow losses. 3D CFD can improve these models with local data, but is much slower. In professional engine projects, both levels are coupled so that system behaviour and detailed physics remain consistent.

Engine load describes how strongly an engine is demanded at a specific operating point. It can be described by torque, mean effective pressure, power, fuel quantity, air mass flow or driver demand. In engine simulation, load strongly influences combustion, temperatures, boost pressure, exhaust enthalpy and emissions. A clear definition of load is important because full load, part load and motored operation represent very different physical states.

An engine map describes the behaviour of an engine over engine speed and load. Typical map quantities include torque, power, fuel consumption, efficiency, boost pressure, air mass flow, exhaust gas temperature and emissions. In 1D engine simulation, maps can be calculated, supplemented or used for concept comparisons. A good engine map shows not only maximum values, but also operating limits such as knock, exhaust gas temperature, turbocharger speed or surge margin.

Engine simulation is the general term for computer-based models of an engine or individual engine systems. It can include 1D engine simulation, 3D CFD, multibody simulation, structural analysis, thermal management or control models. In a narrower context, engine simulation often means 1D calculation of power, torque, fuel consumption, air mass flow and exhaust behaviour. Good engine simulation combines model setup, calibration and test data correlation into a reliable basis for decisions.

Engine speed describes how fast the engine crankshaft rotates. It is usually given in revolutions per minute and is one of the central axes in an engine map. Engine speed influences air mass flow, valve events, friction, turbocharger operation, burn duration and mechanical loading. In 1D engine simulation, it is a fundamental quantity for calculating operating points and transient behaviour.

The equivalence ratio describes the ratio of the actual fuel-air ratio to the stoichiometric fuel-air ratio. It is the inverse of lambda. Values greater than 1 indicate a rich mixture, while values below 1 indicate a lean mixture. The equivalence ratio is especially useful when comparing different fuels such as gasoline, methane and hydrogen.

The excess air ratio lambda describes the ratio between the actual air amount and the stoichiometrically required air amount. Lambda 1 means stoichiometric operation, lambda greater than 1 means lean operation and lambda below 1 means rich operation. Lambda influences efficiency, combustion temperature, NOx, exhaust temperature and ignition stability. In 1D engine simulations, lambda is a central input and target quantity for combustion concepts and calibration.

Exhaust gas temperature describes the temperature of the combustion gases in the exhaust path. It influences turbocharger power, catalyst activity, component protection, aftertreatment and heat input into neighbouring components. In 1D engine simulation, it depends on combustion profile, lambda, efficiency, wall heat loss, gas exchange and pipe heat transfer. Correlation with test data is important because exhaust gas temperatures are strongly dependent on models and boundary conditions.

The exhaust manifold collects exhaust gases from the individual cylinders and guides them to the turbine, aftertreatment system or exhaust line. In 1D engine simulation, it is modelled using pipes, junctions, volumes, heat transfer and pressure waves. Its geometry influences exhaust back pressure, turbocharger excitation, pulse separation, temperature history and cylinder interaction. For turbocharged engines, a realistic exhaust manifold model is especially important for turbo matching and transient response.

Exhaust path simulation calculates the path of combustion gases from the exhaust valve to aftertreatment or ambient. It considers exhaust manifold, turbine, catalysts, filters, pipes, silencers and pressure waves. Important quantities include exhaust back pressure, exhaust enthalpy, turbine power, temperature history and pulsation. Good exhaust path simulation is important for turbocharger design, gas exchange, emissions, thermal management and component temperatures.

An exhaust plenum is a collecting volume in the exhaust system where exhaust flows are merged or stabilized. It can damp pressure pulsations, mix exhaust streams and influence the inflow to downstream components. In 1D engine simulation, it is used to represent volume effects, temperature mixing and pressure dynamics in the exhaust path. Its design is relevant for turbine inflow, exhaust back pressure, aftertreatment and transient behaviour.

Exhaust runner length describes the length of the flow path from the exhaust port to the junction or turbine. It influences pressure waves, pulse separation, exhaust back pressure, residual gas fraction and turbocharger excitation. In turbocharged engines, exhaust runner length can be decisive for how effectively exhaust pulses act on the turbine. In 1D models, it is varied to evaluate gas exchange, turbine power and transient boost build-up.

Fired operation describes engine operation with active combustion. Cylinder pressure, torque, exhaust gas temperature, emissions and thermal loads are generated by fuel conversion. Unlike motored operation, fired operation contains the full coupling of gas exchange, injection, ignition, combustion and exhaust energy. In engine development, it is the relevant state for evaluating power, fuel consumption, efficiency and emissions.

A flame speed model describes how fast the flame propagates under given conditions. It typically considers fuel, lambda, pressure, temperature, residual gas and possibly turbulence influence. In 1D engine simulation, it is an important building block for predictive combustion models such as SITurb. In hydrogen engines, flame speed is especially important because hydrogen burns much faster than many hydrocarbons.

Friction mean effective pressure describes the mechanical friction losses of an engine relative to displacement. It includes losses from the piston ring pack, bearings, valvetrain, auxiliaries and other moving components. In engine simulation, FMEP is used to explain the difference between indicated and brake work. Realistic FMEP modelling is especially important for part-load fuel consumption, efficiency and engine map calculation.

Fuel consumption describes the amount of fuel an engine consumes per time, distance or work output. In engine simulation, it is calculated from fuel mass flow, heating value, efficiency and operating condition. It is a central target quantity for engine concepts, drive cycles, maps and variant comparisons. For reliable interpretation, it must be clear whether instantaneous consumption, cycle consumption or specific fuel consumption is meant.

A full engine model represents the complete engine with its main subsystems. These typically include cylinders, cranktrain abstraction, intake system, exhaust system, turbocharger, charge air cooler, valves, injection, combustion and, where needed, cooling or aftertreatment. It allows calculation of power, torque, fuel consumption, temperatures, mass flow rates and pressure traces over many operating points. The level of modelling detail must match the question, because an overly detailed model can be unnecessarily slow and an overly simplified model can be inaccurate.

Full load describes the operating point at which the engine delivers its maximum possible load or power at a given engine speed. In simulation, boost pressure, air mass flow, fuel quantity, knock limit, exhaust gas temperature and component protection are especially relevant at full load. Full-load points are important for power targets, turbocharger sizing, cooling and mechanical loading. In hydrogen engines, full load must also be matched with excess air, NOx, pre-ignition and backfire risk.

Gas exchange loss describes losses occurring during intake and exhaust gas exchange. Causes include throttling, pressure losses in the intake system, exhaust back pressure, unfavourable valve timing and flow losses at valves and ports. These losses reduce usable engine work and lower brake efficiency. In 1D engine simulation, gas exchange losses can be analysed effectively through pressure traces, mass flow rates and PMEP.

Gas exchange simulation calculates the replacement of exhaust gas by fresh air or fresh mixture in the engine. It considers valve timing, pressure waves, mass flow rates, residual gas fraction, scavenging and cylinder filling. In 1D engine simulation, it is especially important because intake and exhaust systems operate in a strongly unsteady manner. Good gas exchange simulation helps improve torque, fuel consumption, turbocharger excitation and emissions.

Gas exchange describes the replacement of exhaust gas with fresh air or fresh mixture in the engine. It is determined by valve timing, intake system, exhaust system, pressure waves, boosting and residual gas fraction. Combustion describes the chemical conversion of fuel inside the cylinder. It is influenced by mixture formation, ignition, lambda, turbulence, pressure, temperature and combustion chamber geometry. Gas exchange determines the mass, temperature and composition present in the cylinder before combustion. Combustion then determines pressure trace, efficiency, exhaust temperature and emissions. Both processes are strongly coupled because residual gas, filling and charge motion directly change combustion. In 1D engine simulation, this coupling becomes especially visible because air path, exhaust path, cylinder process and combustion model are combined in one system model.

GT-ISE is the graphical working environment within GT-Suite where models are built, parameterized and calculated. Components such as pipes, volumes, cylinders, turbochargers, valves, coolers or control blocks are connected into a simulation model. GT-ISE is therefore the central interface for model setup, variant management and calculation preparation. Reliable results require not only software operation, but also physical understanding of the modelling assumptions.

GT-Post is the postprocessing tool of GT-Suite for simulation results. It is used to display curves, maps, pressure traces, mass flow rates, temperatures, efficiencies and comparison quantities. Good postprocessing is essential because a 1D model generates many signals and operating states. GT-Post helps turn calculation results into engineering conclusions about power, fuel consumption, boosting, gas exchange or thermal management.

GT-Power is a GT-Suite module for 1D engine simulation and engine cycle analysis. It is used to calculate power, torque, air mass flow, fuel consumption, pumping losses, turbo matching, cylinder pressure and thermodynamic processes. The tool enables full engine models including intake system, exhaust path, cylinders, valves, combustion and boosting. For Felsaris, GT-Power is especially valuable because it can connect system simulation and engine expertise with CFD insights.

GT-Suite is the overarching simulation platform from Gamma Technologies for 1D and system simulation. GT-Power is a module within this platform focused on engine cycle simulation and 1D engine simulation. GT-Power is typically used to calculate cylinders, valves, intake systems, exhaust systems, turbochargers, combustion and engine operating points. GT-Suite also covers additional domains such as thermal management, aftertreatment, vehicle models, controls and multi-domain system simulation. In simple terms, GT-Power is the engine simulation tool inside the broader GT-Suite environment. In practice, the terms are sometimes used loosely because GT-Power models are built and evaluated within GT-Suite. For SEO and technical communication, GT-Suite should be explained as the platform and GT-Power as the engine simulation module. This makes clear why Felsaris offers both engine process knowledge and system simulation expertise.

GT-Suite is a commercial simulation platform from Gamma Technologies for 1D and system simulation. In engine development, it is used to model engines, air paths, exhaust paths, boosting, thermal management, aftertreatment and control logic. Its strength lies in combining physical component models, maps, variant calculations and fast system evaluation. GT-Suite is especially relevant when many operating points, transients or concept variants need to be investigated efficiently.

An HC model describes unburned or partially burned hydrocarbons in the exhaust gas. Causes include wall quenching, crevices, wall films, misfire, poor evaporation or incomplete combustion. In 1D engine simulations, HC models are especially relevant for spark-ignition engines, cold start and transient operation. In hydrogen engines, the fuel itself produces no HC emissions, although contributions may come from oil or other carbon sources.

Heat release analysis calculates from the cylinder pressure trace how much heat is released during combustion. It uses thermodynamic assumptions, volume history, gas properties and heat transfer models. The result helps evaluate ignition delay, combustion duration, combustion phasing and multi-stage combustion. In 1D engine simulation, heat release analysis is often used to calibrate combustion profile models and validate the engine cycle model.

The heat release rate describes the rate of heat release during combustion. It is often calculated from the cylinder pressure trace and shows when chemical energy is converted into heat. Unlike the combustion profile, the heat release rate is a rate and shows the intensity of heat release over crank angle. In engine simulation, it is important for combustion analysis, combustion modelling and calibration.

A heat transfer model describes how heat is transferred between gas and wall during the engine process. In 1D engine simulation, it is needed to calculate wall heat losses, gas states, exhaust gas temperature and efficiency. Empirical or semi-empirical models are often used because the real processes in the combustion chamber are highly complex. The choice and calibration of the heat transfer model strongly affect combustion analysis, engine cycle simulation and thermal assessment.

The Hohenberg model is an empirical heat transfer model for calculating wall heat losses in engines. It uses a different correlation than the Woschni model and is also commonly used in engine cycle simulations. Depending on engine, operating point and combustion concept, it can produce different heat transfer values and therefore different pressure and temperature traces. In practice, the model should be validated using cylinder pressure, exhaust gas temperature and energy balance.

Hydrogen consumption describes the amount of hydrogen required by a hydrogen engine or fuel cell system during operation. In H2ICE simulations, it depends on efficiency, lambda, boost pressure, combustion profile, losses and operating strategy. Because hydrogen has low density, storage demand and tank volume are important in addition to mass consumption. For comparisons with other fuels, heating value and system efficiency must be considered.

IMEP means indicated mean effective pressure and describes the work generated inside the cylinder relative to displacement. BMEP means brake mean effective pressure and describes the usable work at the crankshaft relative to displacement. IMEP is calculated from the cylinder pressure trace and is closer to the combustion process. BMEP is directly related to usable torque and brake engine power. The difference between IMEP and BMEP results from friction, pumping losses and auxiliaries. IMEP is useful for evaluating combustion, cylinder to cylinder variation and cycle to cycle variation. BMEP is better for comparing power density and real engine performance. In engine simulation, both quantities are needed to separate the thermodynamic process from usable output power.

Indicated efficiency describes how efficiently the chemical fuel energy is converted into indicated work inside the cylinder. It is evaluated before mechanical losses and is therefore useful for assessing the combustion process. Influencing factors include combustion profile, combustion phasing, wall heat loss, gas exchange, exhaust losses and compression ratio. In model calibration, indicated efficiency is an important target quantity for correlating pressure trace and combustion profile.

Indicated efficiency describes how well fuel energy is converted into indicated work inside the cylinder. It evaluates the thermodynamic process before mechanical losses. Brake efficiency describes how much fuel energy arrives as usable power at the crankshaft. It additionally includes friction, pumping losses and auxiliary losses. Therefore, brake efficiency is always lower than indicated efficiency. Indicated efficiency is especially useful for evaluating combustion concept, combustion phasing, combustion profile and wall heat losses. Brake efficiency is more relevant for the vehicle, customer and fuel consumption because it describes real usable engine output. The difference between both quantities shows how strongly mechanics, gas exchange and auxiliaries degrade the engine process.

Indicated mean effective pressure describes the work generated inside the cylinder relative to displacement. It is calculated from the cylinder pressure trace and is useful for comparison independent of engine size. IMEP is used to evaluate combustion, load, cylinder to cylinder variation and cycle to cycle variation. Mechanical losses are not yet included, so IMEP is closer to the thermodynamic combustion process than BMEP.

Injection duration describes how long an injector remains open during an injection event. Together with injection pressure, injector geometry and fuel properties, it determines the injected fuel quantity. Longer injection duration may be necessary at high load, but often reduces the available mixing time. In simulation, it is important for mixture formation, combustion profile and cylinder to cylinder distribution.

Injection timing describes when fuel is introduced during the engine cycle. It influences mixture formation, evaporation, wall contact, ignition delay, combustion profile and emissions. Early injection provides more mixing time, but can promote wall wetting or reverse flow effects. Late injection enables stratification and targeted load control, but requires rapid and stable mixing.

The intake plenum is a collecting volume in the intake system that distributes air or mixture to multiple intake runners. It acts as a pressure reservoir and influences pressure pulsations, cylinder filling, distribution uniformity and response. In 1D engine simulation, it is usually represented as a volume model with multiple inlets and outlets. Plenum size, shape and connection layout can significantly affect torque curve, gas exchange and cylinder to cylinder distribution.

The intake runner is the individual flow passage leading from the intake manifold or plenum to a cylinder. Length, diameter, volume and cross-section distribution influence pressure waves, resonance charging, cylinder filling and distribution uniformity. In 1D engine simulation, the intake runner is modelled as a pipe with real losses and wave propagation. Its design is especially important for torque curve, response and gas exchange.

Intake runner length describes the length of the flow path from the plenum or intake manifold to the cylinder intake port. It influences pressure wave travel time, resonance effects, cylinder filling and torque curve. Long intake runners often support lower engine speeds, while short runners tend to support higher engine speeds. In 1D engine simulation, intake runner length is an important tuning variable for gas exchange optimization and variant calculation.

A knock model evaluates the engine’s tendency for knocking combustion. It uses quantities such as pressure, temperature, fuel data, residual gas, mixture composition and residence time of the end gas. In 1D engine simulation, a knock model can help secure spark timing, boost pressure, compression ratio and cooling. Its quality strongly depends on calibration and test data correlation because knock is highly sensitive to local conditions.

A load step is a rapid change in engine load, for example from part load to high load. In 1D engine simulation, a load step is used to analyse torque build-up, boost dynamics, air path filling, exhaust enthalpy and control behaviour. Especially in turbocharged engines, a load step shows how strongly turbo lag, overshoot or delays occur. For calibration, it is important because drivability, component protection, knock limit and emissions must be controlled at the same time.

A manifold model describes the flow in an intake or exhaust manifold. It represents branches, junctions, pressure waves, heat transfer and cylinder to cylinder interactions. In the intake manifold, it affects cylinder filling and distribution uniformity, while in the exhaust manifold it affects back pressure and turbocharger excitation. For turbocharged engines, a good manifold model is especially important for turbo matching and transient response.

Map extrapolation means extending a map beyond the measured or available range. This may be necessary when a simulation point lies outside the available data. Extrapolation is always less certain than interpolation within a map. Especially for turbocharger maps, surge limits, choke limits and efficiency islands, map extrapolation must be checked critically.

Map scaling describes adapting an existing component map to a similar but not identical component or operating condition. In engine simulation, it is often used for turbochargers, coolers, pumps or flow components. Quantities such as mass flow, pressure ratio, efficiency or speed are scaled. Map scaling is practical, but must be validated plausibly because it can lead to errors outside proven measurement ranges.

Map scaling adapts an existing map to a similar component or changed operating condition. For example, mass flow, pressure ratio, speed or efficiency are modified using scaling factors. Map extrapolation extends a map beyond the available measurement or data range. Scaling usually remains closer to a known physical basis, provided the new component is truly similar. Extrapolation is riskier because there is no measurement support outside the data base. Especially for turbocharger maps, surge line, choke line and efficiency islands can be strongly misestimated outside the measured range. Both methods are useful in early project phases, but must be clearly identified. For reliable decisions, scaled or extrapolated maps should later be secured using supplier data, test bench data or validated 3D CFD.

Mass fraction burned describes what fraction of the fuel mass has already been converted at a given crank angle. Typical values are MFB10, MFB50 and MFB90. These values are used to derive start of combustion, combustion phasing and combustion duration. In 1D engine simulation, mass fraction burned is a central quantity for combustion models and pressure trace analysis.

Mass fraction burned 50 percent describes the crank angle at which 50 percent of the fuel mass has burned. It is often used as a measure of combustion phasing because it represents the position of the main heat release well. If MFB50 is too early, knock, high pressure rise rates and high component loads can occur. If MFB50 is too late, efficiency, torque and exhaust temperature usually deteriorate.

Mechanical efficiency describes the ratio between brake work at the crankshaft and indicated work inside the cylinder. It shows what fraction of the work generated in the cylinder remains after friction and mechanical losses. Influencing factors include cranktrain friction, valvetrain, piston ring pack, bearings, oil viscosity and auxiliaries. Mechanical efficiency is especially important at part load because friction losses are relatively significant there.

Model calibration means adjusting model parameters so that the simulation model reproduces known measurement data or reference states as well as possible. In engine simulation, this can include combustion profile, friction, heat transfer, flow coefficients, turbocharger maps or pressure losses. Calibration should not be understood as arbitrary tuning, but must remain physically plausible. A well-calibrated model can then be used for variants, operating points and concept decisions.

Model reduction describes simplifying a complex model without losing the relationships that are important for the engineering question. In engine simulation, a detailed 3D or full system model can be reduced to maps, correlations or simplified components. The goal is shorter computation time with sufficient accuracy. Model reduction is especially useful for variant studies, optimization, control development and early concept phases.

Model setup describes the process of turning an engineering question into an executable simulation model. This includes selecting model boundaries, components, geometries, maps, boundary conditions and physical submodels. In 1D engine simulation, model setup strongly affects runtime, stability and the value of the results. A clean model setup therefore starts with the question of whether architecture, component cause, operating strategy, calibration or validation evidence is being investigated.

Model validation checks whether a simulation model represents the real physics with sufficient accuracy for the intended application. Simulation results are compared with test bench data, vehicle measurements, component measurements or reliable reference cases. Validation does not only answer whether a model runs, but whether its predictions are reliable. In 1D engine simulation, validation is especially important because many results come from simplified component models and maps.

Motored operation describes engine operation without combustion, where the engine is driven externally. It is used to investigate friction, pumping losses, gas exchange, pressure traces and mechanical base losses. In simulation, motored operation helps check model contributions without the influence of combustion. Comparing motored and fired operation is important to separate friction, gas exchange and combustion contributions clearly.

A NOx model describes the formation of nitrogen oxides during combustion. It typically uses quantities such as temperature, oxygen concentration, residence time, pressure and mixture composition. In hydrogen engines, a NOx model is especially important because the fuel produces no carbon-based emissions, but NOx can still occur. In 1D simulations, NOx prediction must be carefully calibrated because local combustion chamber temperatures are represented only in simplified form.

One-dimensional CFD describes the numerical calculation of flows in networks of pipes, volumes and components. In engine applications, it is mainly used to represent unsteady gas exchange in intake and exhaust systems. Pressure waves, mass flow rates, temperatures and component maps can be calculated over the engine cycle. 1D CFD is not a replacement for 3D CFD, but a fast system-level approach with different modelling assumptions.

An operating point describes a specific engine state with a defined load demand. It is often defined by engine speed, torque, mean effective pressure, boost pressure, fuel quantity or power. In simulation, an operating point is used to analyse a specific operating state deliberately. Operating points are important for map generation, calibration, fuel consumption evaluation, emissions and component protection.

An operating point is a defined state in which an engine or subsystem is operated. It usually includes engine speed, load, temperatures, pressures, mass flow rates and possibly control variables. The term is slightly more general than load point and can also refer to cooling circuits, turbochargers, aftertreatment or components. For reliable simulations, operating points must be clearly described and calculated with suitable boundary conditions.

A parameter study systematically investigates how changes in individual model quantities affect the simulation result. In 1D engine simulation, examples include boost pressure, valve timing, compression ratio, EGR rate, turbocharger size or combustion profile. Parameter studies help understand cause-effect relationships and identify sensitive input quantities. They are especially useful when many technical options must be evaluated quickly in an early project phase.

Part load describes engine operation below the maximum possible load. Engines operate in this range very frequently in real use, making fuel consumption, efficiency and emissions especially important. In spark-ignition engines, throttling losses and spark strategy can strongly influence part-load efficiency. In 1D engine simulation, part load is important for map fuel consumption, hybrid strategy, EGR, warm-up behaviour and drive cycles.

Pipe friction loss is caused by friction between the flowing gas and the pipe wall. It leads to pressure loss and reduces available energy in the intake or exhaust system. In 1D engine simulations, it is calculated using pipe length, diameter, roughness, Reynolds number, flow velocity and fluid properties. Realistic pipe friction losses are important for air mass flow, pumping losses, exhaust back pressure and turbocharger operation.

Pipe heat transfer describes heat exchange between the flowing gas and the pipe wall. In the exhaust path, it influences exhaust gas temperature, turbine energy, catalyst light-off and component temperatures. In the intake path, heat transfer can affect charge air temperature, density and knock tendency. In 1D engine simulations, pipe heat transfer modelling is important for transient temperature histories and thermal management.

A pipe model describes one-dimensional flow in a duct or pipe. It considers length, diameter, cross-section, friction, heat transfer, pressure waves and, where relevant, gas composition. In intake and exhaust systems, pipe models are important because pressure waves and travel times influence gas exchange. A correct pipe model is especially relevant for resonance effects, pulsations, exhaust routing and transient simulations.

A plenum model describes a larger collecting volume in the intake or exhaust system. It is used to calculate pressure, temperature, mass and mixture in a volume with multiple inlets and outlets. Plenums can damp pressure oscillations, distribute flows or act as accumulators. In 1D engine simulations, the plenum affects filling, dynamics, cylinder distribution and control behaviour.

PMEP means pumping mean effective pressure and describes gas exchange work relative to displacement. FMEP means friction mean effective pressure and describes mechanical friction losses relative to displacement. PMEP results from intake, exhaust, throttling, exhaust back pressure, valve timing and pressure losses in the air and exhaust path. FMEP results from piston rings, bearings, cranktrain, valvetrain, oil viscosity and auxiliaries. PMEP depends strongly on operating point and gas exchange strategy. FMEP depends more strongly on engine mechanics, speed, temperature and lubrication. Both quantities reduce the difference between indicated and brake work. In 1D engine simulation, PMEP can be analysed particularly well through pressure traces in the intake and exhaust systems, while FMEP is usually calibrated using friction models or measurement data.

A predictive combustion model calculates the combustion profile from physical influencing quantities instead of simply prescribing it. Depending on the model, it considers turbulence, flame speed, mixture state, pressure, temperature, residual gas fraction and combustion chamber geometry. This enables better representation of changes in operating point, fuel, charge motion or boosting than a simple Wiebe function. However, parameterization, calibration and validation require more effort.

A Vibe or Wiebe function describes the combustion profile using a prescribed mathematical curve. It is robust, fast and very useful when a measured combustion profile needs to be reproduced or a known operating point needs calibration. A predictive combustion model calculates the combustion profile more strongly from physical influencing variables. These include turbulence, flame speed, lambda, pressure, temperature, residual gas fraction and combustion chamber geometry. The Wiebe function is simpler and more stable, but has limited predictive capability for new geometries or significantly changed operating strategies. A predictive model requires more effort for parameterization and validation, but can evaluate variants more realistically. Especially for hydrogen engines, gas engines and modified charge motion, a predictive approach is often valuable. In practice, the Wiebe function is good for calibration and map calculation, while predictive models are stronger for concept development and physical extrapolation.

A pre-ignition model attempts to estimate the risk of unintended ignition before the intended spark timing. Influencing factors include hot surfaces, pressure, temperature, fuel, oil, deposits, mixture distribution and local reaction conditions. In 1D engine simulations, prediction is more difficult than for many standard quantities because pre-ignition strongly depends on local and partly stochastic triggers. Conservative assessment is especially important in highly boosted spark-ignition engines and hydrogen engines.

Pressure indication refers to high-resolution measurement of cylinder pressure over crank angle. It provides the basis for combustion analysis, heat release analysis, mean effective pressure calculation and knock assessment. In engine development, pressure indication links test bench measurement and simulation because it reveals the real thermodynamic process in the cylinder. Accurate pressure indication requires suitable sensors, crank angle reference, signal processing and thermal corrections.

A pressure loss model describes the pressure drop of a component or flow section as a function of mass flow, density, temperature and geometry. It is used for air filters, coolers, pipes, manifolds, valves, catalysts or restrictions. Pressure losses influence air mass flow, pumping losses, turbocharger work and efficiency. In 1D engine simulation, realistic pressure loss models are important for correctly representing system behaviour and operating limits.

Pressure trace analysis evaluates measured or simulated cylinder pressure over crank angle. Quantities such as indicated mean effective pressure, heat release rate, combustion phasing, combustion duration, pressure rise rate and peak cylinder pressure are calculated from it. It shows whether ignition, combustion, gas exchange and heat losses match the expected engine behaviour. In 1D engine simulation, it is an important tool for model calibration and test data correlation.

A pressure wave is a propagating pressure disturbance in a gas or fluid. In engine intake and exhaust systems, pressure waves are generated by valve opening, valve closing, combustion, piston motion and turbocharger interaction. They influence cylinder filling, residual gas fraction, turbine excitation and resonance effects. 1D engine simulation is particularly strong at representing these unsteady wave phenomena efficiently across pipes and volumes.

Pressure wave reflection occurs when a pressure wave reaches a change in cross-section, a valve, an open pipe end, a plenum or a junction. Part of the wave is reflected and can superimpose with other waves. In an engine, this superposition can improve or reduce cylinder filling. The targeted use of pressure wave reflection is important for intake runner lengths, exhaust manifolds, resonance charging and pulse charging.

Pumping loss is the work the engine must spend for gas exchange. It arises from throttling losses in the intake system, exhaust back pressure or unfavourable pressure conditions during intake and exhaust. Especially in spark-ignition engines at part load, pumping losses can be significant. Measures such as variable valve timing, unthrottled operation, boosting or EGR can reduce pumping losses depending on the operating point.

Pumping mean effective pressure describes the work required or recovered during intake and exhaust gas exchange. It is closely linked to throttling, exhaust back pressure, valve timing, boosting and gas exchange. An unfavourable PMEP reduces brake efficiency even if combustion itself is good. In 1D engine simulations, PMEP is an important quantity for evaluating the air path, exhaust path and valve strategy.

RDE simulation describes evaluation of a powertrain in realistic driving operation under varying environmental and driving conditions. RDE stands for Real Driving Emissions and is especially relevant for emission behaviour outside a classical test bench cycle. The simulation considers load dynamics, thermal management, aftertreatment, altitude, ambient temperature and driving profile. For modern engines, RDE simulation is important for securing robust emission strategies across broad operating ranges.

Residual gas fraction describes the fraction of burned gas remaining in the cylinder or reintroduced through EGR. It affects oxygen concentration, combustion temperature, ignition behaviour, knock tendency and NOx formation. A moderate residual gas fraction can improve emissions and pumping losses. Too much residual gas can reduce combustion stability, torque and ignitability.

Resonance charging uses pressure waves in the intake system to improve cylinder filling in certain engine speed ranges. With suitable intake runner lengths and volumes, a positive pressure wave can arrive at the intake valve at the right time. This allows more air or mixture to enter the cylinder without requiring a turbocharger. In 1D engine simulation, resonance charging can be investigated very effectively because runner lengths, plenum volumes and valve timing can be varied quickly.

A simulation model is a simplified computational representation of a real technical system. In 1D engine simulation, it consists of components, equations, maps, boundary conditions and calibration parameters. A good model is as detailed as necessary and as simple as possible. The key is that model structure, assumptions and validation status match the engineering question.

A simulation run is a single calculation of a simulation model with defined inputs, boundary conditions and settings. It can represent a steady-state operating point, a load step, a drive cycle or a variant calculation. For traceable results, version, parameters, model state and postprocessing must be documented. In 1D engine simulation, many simulation runs are used to build maps, sensitivities and technical decision bases.

An SI turbulence combustion model describes the influence of turbulence on flame propagation and burning velocity in spark-ignition engines. It links quantities such as turbulent kinetic energy, length scales, flame speed and combustion chamber state. In 1D engine simulations, such a model is used to calculate the combustion profile more predictively. Turbulence modelling is especially important when intake ports, valve strategies, swirl, tumble or hydrogen operation are changed.

SITurb is a predictive combustion model for spark-ignition engines in GT-Power or GT-Suite. It models turbulent flame propagation in the combustion chamber and uses inputs such as turbulence, flame speed, mixture state and combustion chamber geometry. The model is especially interesting for gasoline, gas and hydrogen engines where changes in charge motion, lambda or spark timing need to be evaluated. For reliable results, the model parameters must be carefully correlated with cylinder pressure and combustion analysis.

A soot model describes soot particle formation and oxidation during combustion of carbon-containing fuels. It is especially relevant for diesel engines, direct injection and locally rich mixture zones. Influencing factors include mixture formation, temperature, oxygen availability, pressure, injection strategy and residence time. In hydrogen engines, fuel-derived soot formation is not relevant because hydrogen contains no carbon.

Spark timing describes when the spark is triggered relative to crankshaft position. It influences combustion phasing, efficiency, torque, exhaust temperature and knock tendency. Advanced spark timing can improve efficiency, but can increase pressure rise and knock risk. In 1D engine simulations, spark timing is often used as a calibration variable or optimization parameter.

A speed step describes a rapid change in engine speed. It can be used in test bench experiments or simulations to evaluate dynamic engine behaviour, turbocharger operation, air path inertia and control. Engine speed directly influences mass flow rates, valve events, friction, pumping losses and combustion duration. In 1D engine simulation, a speed step helps check the model response to unsteady operating changes.

Steady-state engine simulation calculates operating points where engine speed, load, temperatures, pressures and mass flow rates are assumed to be constant over time. It is well suited for maps, model calibration, full-load curves, part-load points and basic concept comparisons. Transient engine simulation calculates time-dependent processes such as load steps, drive cycles, warm-up, turbocharger acceleration and control behaviour. This reveals storage effects, delays, overshoot and thermal inertia. Steady-state simulation is faster and often sufficient when averages or stable operating points are of interest. Transient simulation is required when drivability, real-world emissions, turbo lag or temperature history must be evaluated. Especially in turbocharged engines, steady-state results cannot fully describe real response behaviour. In development, steady-state maps are often built first and then supplemented with transient simulations for real manoeuvres.

A steady-state operating point is an engine state in which engine speed, load, temperatures, pressures and mass flow rates are largely constant over time. Such points are well suited for map generation, model calibration, test data correlation and basic design. In simulation, steady-state operating points are usually easier and faster to evaluate than transient manoeuvres. However, they do not represent dynamic effects such as turbo lag, warm-up, load steps or control behaviour.

The surge line describes the region of unstable compressor operation at too low mass flow and too high pressure ratio in the compressor map. In this region, the flow can periodically break down or even briefly reverse. In an engine, surge can cause pressure oscillations, noise, poor drivability and high mechanical loading. In 1D engine simulation, the distance to the surge line is evaluated for steady-state and transient operating points.

System simulation does not focus on a single component, but on the behaviour of an interconnected complete system. In engine development, this can include air path, exhaust path, turbocharger, cylinders, cooling, aftertreatment and control. The advantage is that interactions become visible which may be missed when components are analysed in isolation. System simulation is especially important for operating strategy, transients, maps, variant comparisons and early concept decisions.

Test data correlation describes the comparison of simulation results with measured data. Typical comparison quantities include torque, power, air mass flow, boost pressure, exhaust gas temperature, cylinder pressure, fuel consumption and emissions. The correlation shows whether model assumptions, maps, boundary conditions and calibration parameters match the real engine. Without test data correlation, an engine simulation remains more of a concept calculation than a reliable prediction.

A throttle model describes the flow and pressure loss at a throttle valve or restriction. It considers opening angle, effective area, pressure ratio and flow state. In spark-ignition engines, the throttle strongly influences load control, pumping losses and transient response. In simulation, a good throttle model is important for part-load operation, drive cycles and control models.

A transient drive cycle describes a time-dependent operating sequence with changing engine speed, load, gear selection, temperatures and control variables. In 1D engine simulation, it is used to evaluate real driving behaviour, fuel consumption, emissions, turbocharger response and thermal management over time. Compared with steady-state operating points, a drive cycle reveals dynamic effects such as load steps, warm-up, boost build-up and control behaviour. This is important for modern powertrains because many critical emissions and temperature states occur during transient operation.

Transient engine simulation calculates time-dependent changes in engine speed, load, pressures, temperatures, mass flow rates, turbocharger speed and control variables. It is important for load steps, drive cycles, warm-up, boost build-up, emissions and thermal behaviour. Unlike steady-state simulation, it reveals delays, overshoot, storage effects and control interactions. For turbocharged engines and hybrid powertrains, transient engine simulation is especially valuable.

Turbine inlet temperature is the exhaust gas temperature directly upstream of the turbine. Together with mass flow and pressure ratio, it determines the available exhaust enthalpy for the turbocharger. Excessive turbine inlet temperatures can load the turbine wheel, housing, bearings and materials. In 1D engine simulation, it is monitored as an important limit for full load, boost strategy, component protection and turbo matching.

The turbine map describes the behaviour of a turbocharger turbine in terms of exhaust mass flow, pressure ratio, speed and efficiency. It shows how effectively exhaust enthalpy is converted into shaft power for the compressor. In 1D engine simulations, it affects exhaust back pressure, turbocharger speed, boost build-up and exhaust temperature. For turbocharger matching, the turbine map must always be evaluated together with the compressor map.

Turbocharger efficiency describes how efficiently turbine and compressor convert energy together. It consists of compressor efficiency, turbine efficiency and mechanical losses in the shaft and bearings. High efficiency reduces exhaust back pressure, charge air temperature and energy losses. In 1D engine simulation, turbocharger efficiency directly affects fuel consumption, boost pressure, exhaust temperature and transient behaviour.

Turbocharger matching means selecting and calibrating a turbocharger for an engine and its operating range. Compressor map, turbine map, boost target, air mass flow, exhaust energy, efficiency and operating limits are evaluated together. The goal is a good compromise between response, maximum power, fuel consumption, surge margin and thermal safety. 1D engine simulation is particularly suitable because many operating points and variants can be calculated quickly.

A turbocharger model represents compressor, turbine, shaft, inertia, efficiencies and control elements such as wastegate or VGT. It links exhaust gas energy with compression of the intake air. Good turbocharger models require reliable compressor and turbine maps as well as suitable assumptions for heat transfer and friction. In engine simulation, the turbocharger model is decisive for boost pressure, exhaust back pressure, air mass flow and transient response.

Turbocharger speed describes the rotational speed of the common shaft of turbine and compressor. It is an important operating limit because excessive speed strongly loads bearings, compressor wheel, turbine wheel and structural integrity. Turbocharger speed depends on exhaust energy, turbine map, compressor work, wastegate or VGT position and transient operation. In simulation, it is monitored to avoid overspeed and unacceptable operating regions.

The valve lift profile describes valve lift over crank angle. It determines when a valve opens, how quickly it opens, how long it remains open and when it closes again. The lift profile influences flow, gas exchange, residual gas fraction, valve overlap and pumping losses. In 1D engine simulation, it is a central input for valve models and gas exchange calculation.

A valve model describes the time-dependent flow through intake or exhaust valves. It uses valve lift profile, discharge coefficients, effective flow area and pressure ratios. The valve model is decisive for gas exchange, residual gas fraction, pumping losses and cylinder filling. In 1D engine simulation, it must be well correlated with measurement data or 3D CFD flow data.

Valve timing describes the opening and closing timings of intake and exhaust valves. It influences cylinder filling, residual gas fraction, valve overlap, scavenging, pumping losses and torque curve. Variable valve timing enables adaptation to engine speed, load and operating strategy. In 1D engine simulations, valve timing is especially important for gas exchange optimization, Miller cycle, Atkinson cycle and turbo matching.

A variable turbine geometry model describes a turbine with adjustable geometry. It represents how vane position or effective turbine flow area changes mass flow, pressure ratio, efficiency and turbine power. VGT strongly affects response at low engine speed and exhaust back pressure at high load. For simulation, suitable maps or correction functions over VGT position are essential.

Variant calculation means calculating several technical variants with a comparable simulation model. Examples include different turbochargers, valve timings, charge air coolers, pipe lengths, combustion profiles or operating strategies. The advantage of 1D engine simulation is that many variants can be compared with relatively short runtimes. It is important that boundary conditions and evaluation remain consistent so that the differences truly come from the variant.

Wall heat loss describes the portion of combustion heat transferred to combustion chamber walls, piston, cylinder head and cylinder liner. It reduces indicated efficiency, but also protects components from overheating. In 1D engine simulations, wall heat loss is usually represented through empirical heat transfer models. Correct modelling is important for cylinder pressure, exhaust gas temperature, component temperatures and efficiency.

A wastegate model describes the behaviour of the bypass valve that can route exhaust gas around the turbine. It considers opening position, flow area, pressure ratio, actuator behaviour and control strategy. The wastegate influences boost pressure, turbocharger speed, exhaust back pressure and thermal loading. In 1D engine simulation, a realistic wastegate model is important for full load, part load and transient load steps.

A wastegate model describes a bypass valve that can route exhaust gas around the turbine. It influences boost pressure, turbocharger speed, exhaust back pressure and exhaust gas temperature. A VGT model describes a turbine with variable geometry, usually through vane position or effective turbine area. This allows the turbine to be actively adapted over a wider operating range. The wastegate model is conceptually simpler and mainly represents opening and closing of a bypass path. The VGT model is more complex because mass flow behaviour, efficiency and turbine power change with geometry position. For transient 1D engine simulations, both models are highly relevant for control. Wastegate systems are simpler and robust, while VGT systems offer more degrees of freedom for response, boost build-up and exhaust back pressure.

Wave propagation describes how pressure, temperature or velocity signals move along pipes and ducts. In engines, it is central to gas exchange because pressure waves in the intake and exhaust systems interact with valve events. Pipe length, temperature, gas composition and flow velocity influence wave travel time and wave strength. In 1D engine simulation, correct wave propagation is decisive for resonance charging, pulse charging and transient gas dynamics.

Vibe function is a spelling used in some software environments or translations for the Wiebe function. It describes mass fraction burned over crank angle using a mathematical S-shaped curve. In 1D engine simulation, it is used to represent a prescribed combustion profile in a simple and robust way. From a terminology perspective, the spelling Wiebe function is preferred when referring to the established combustion model name.

The Wiebe function is a mathematical function used to describe mass fraction burned over crank angle. In engine cycle simulation, it is often used to prescribe start of combustion, combustion duration and the shape of the combustion profile. With only a few parameters, it can represent a plausible combustion profile for spark-ignition, diesel or gas engines. Its advantage is robust application, while its limitation is restricted predictive capability when geometry or mixture formation changes strongly.

Wiebe parameters are the tuning quantities of a Vibe or Wiebe function. They typically determine start of combustion, combustion duration, shape factor and combustion completeness. These parameters can be used to match a simulated combustion profile to a measured pressure trace. The parameters should remain physically plausible because a purely mathematical fit can otherwise produce incorrect conclusions about efficiency, temperature and knock tendency.

WLTP simulation describes calculation of a powertrain over the Worldwide Harmonized Light Vehicles Test Procedure. It is used to assess fuel consumption, CO2, emissions, warm-up and operating strategy under defined test conditions. For combustion engines, cold start, aftertreatment, part-load efficiency and transient load changes are especially important. 1D engine simulation can support WLTP assessments before full test bench or vehicle measurements are available.

The Woschni model is a well-known empirical heat transfer model for internal combustion engines. It describes heat transfer between cylinder gas and combustion chamber wall using quantities such as pressure, temperature, bore and characteristic gas velocity. The model is often used in 1D engine cycle simulations because it is robust and well established. Its parameters must match engine type, combustion concept and test data correlation.