1D engine simulation

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.

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.

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.

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 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.

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.

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 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 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.

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 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.

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.

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 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.

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.

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 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.

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 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.

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.