internal combustion engine

The combustion chamber is the region where air, fuel and possibly residual gas are mixed, compressed and burned. Its geometry is shaped by the cylinder head, piston, valves, spark plug and injectors. The combustion chamber influences charge motion, mixture formation, flame propagation, wall heat losses, knock tendency, emissions and efficiency. In development, it is one of the most important levers for modern spark-ignition, diesel, gas and hydrogen engines.

The combustion chamber roof is the upper part of the combustion chamber within the cylinder head. It typically includes valve seats, spark plug location, injector position and surrounding wall surfaces. Its shape influences compression, charge motion, flame propagation, heat transfer and local thermal loading. Especially in compact combustion chambers, high power density or hydrogen operation, the combustion chamber roof is relevant for knock and pre-ignition risks.

A compression-ignition engine is an internal combustion engine in which fuel is injected into hot, highly compressed air and ignites by itself. Power is typically controlled by the injected fuel quantity rather than by conventional throttling of the air path. Important development parameters include injection pressure, injection strategy, mixture formation, ignition delay, soot formation, NOx emissions and exhaust aftertreatment. Diesel engines often achieve high efficiency, but place high demands on combustion, injection system and emission control.

The connecting rod links the piston and crankshaft and transfers forces from combustion and mass acceleration. It is exposed to alternating tensile and compressive loads and must provide high strength at low weight. Its length, stiffness and mass influence kinematics, friction, piston side forces and vibration behaviour. In engine development, the connecting rod is an important component for durability and mechanical efficiency.

The crankcase houses the crankshaft, bearings, oil volume and often other engine components. It is a central structural component of the engine and must carry loads from combustion, mass acceleration and bearing forces. In addition to strength and stiffness, oil management, ventilation, friction, NVH behaviour and manufacturing are important. In modern engines, the crankcase also affects packaging, thermal management and system integration.

The crankshaft converts the linear motion of the pistons into rotary motion through the connecting rods. It transfers engine torque to the drivetrain, generator or driven machine. Important development aspects include strength, torsional vibrations, bearing loads, lubrication, mass balancing and friction. In high-performance and heavy-duty engines, the crankshaft is especially loaded by high cylinder pressures and continuous operation.

The cylinder is the working space in which the piston moves and the combustion process takes place. Together with the cylinder head, piston, valves and, where used, cylinder liner, it forms the combustion chamber and guides the piston. Cylinder geometry, surface, cooling and sealing influence friction, oil consumption, heat transfer and durability. In simulation, the cylinder is a central region for charge motion, combustion and thermal loading.

The cylinder head closes the combustion chamber at the top and usually contains intake ports, exhaust ports, valves, spark plug or injectors. It influences charge motion, mixture formation, heat transfer, knock tendency, combustion speed and component temperatures. Especially in hydrogen engines and high-performance engines, cylinder head design is critical for safe combustion and cooling. Changes to the cylinder head always affect flow, combustion, mechanics and thermal management.

The cylinder liner is the cylindrical running surface in which the piston and piston rings move. It can be designed as a separate component or as a machined surface in the engine block. The cylinder liner affects friction, wear, oil consumption, sealing and heat transfer to the cooling system. Material, coating, surface texture and thermal integration are decisive for durability and efficiency.

The cylinder wall is the surface along which the piston and piston rings move. It influences friction, wear, oil film behaviour, sealing, heat transfer and blow-by. Surface structure, material, coating and lubrication are decisive for efficiency and durability. From a thermal perspective, the cylinder wall is an important interface between the hot combustion chamber, piston ring pack and engine cooling.

Downsizing means reducing engine displacement while maintaining or increasing engine power. This is usually achieved through boosting, direct injection, higher mean effective pressures and optimized combustion. The goal is lower fuel consumption in real operation, especially when the engine operates more often in efficient load regions. Challenges include knock, thermal loading, exhaust temperature, transient boost build-up and durability.

A dual-fuel engine uses two fuels or two different combustion contributions within one operating concept. Often, a gaseous main fuel is ignited by a small amount of diesel or another pilot fuel. The goal is to combine advantages such as high efficiency, alternative fuels or lower CO₂ emissions with reliable ignition. Development is complex because mixture formation, ignition behaviour, load control, emissions and fuel shares must be matched across the operating range.

Engine development includes the technical design, optimization and validation of an engine. It covers mechanics, thermodynamics, gas exchange, combustion, boosting, cooling, friction, emissions and control. Modern engine development combines test bench work, 1D engine simulation, 3D CFD, measurement data analysis and component simulation. The goal is an engine that achieves the required operating conditions reliably, efficiently and with low emissions.

A four-stroke engine operates with the four strokes intake, compression, power and exhaust. The crankshaft requires two revolutions for one complete working cycle. This concept is widely used in passenger car, commercial vehicle, motorcycle, industrial and racing engines. The clear separation of strokes enables good control of gas exchange, combustion and emissions.

A gas engine is an internal combustion engine operated with gaseous fuels such as natural gas, biogas, hydrogen or synthesis gas. Depending on the concept, it can be designed as a spark-ignition engine or as a dual-fuel engine. Important topics include mixture formation, methane number, knock resistance, ignition energy, lean operation and exhaust emissions. Gas engines are often used in combined heat and power plants, industrial systems, commercial vehicles and stationary applications.

A heavy-duty engine is an engine for vehicles such as trucks, buses, construction machines, agricultural machines or special vehicles. It is designed for high continuous power, high torque, robustness, efficiency and long service life. Important topics include exhaust aftertreatment, boosting, thermal management, fuel consumption, operating strategy and real-world emissions. For alternative fuels such as hydrogen or methane, packaging, range, tank concept and durability also play a major role.

A high-performance engine is designed for high specific power, high engine speeds, high mean effective pressures or demanding dynamic requirements. This significantly increases the demands on combustion, boosting, cooling, lubrication, strength and control. Typical development targets are high power density, rapid load response, thermal stability and reproducible performance. High-performance engines are used in motorsport, performance vehicles, aviation applications and special industrial drives.

A hybrid powertrain combines at least two energy converters or energy storage systems, usually an internal combustion engine and an electric motor with a battery. This allows the combustion engine to operate at more favourable points, while the electric motor enables recuperation, boosting and electric driving. For engine development, this changes load profiles, start-stop frequency, warm-up behaviour, exhaust aftertreatment and thermal management. Hybridization can reduce fuel consumption and emissions, but significantly increases system complexity.

A hydrogen combustion engine is an internal combustion engine that uses hydrogen as fuel. Hydrogen burns very quickly, has wide flammability limits and requires only low ignition energy. This enables lean mixtures and high efficiencies, but also increases the demands on mixture formation, backfire, pre-ignition, knock and NOx prevention. In development, combustion chamber, injection strategy, charge motion, ignition and boosting are strongly coupled.

A hydrogen dual-fuel engine combines hydrogen with a second fuel or ignition concept. Hydrogen often acts as the main energy carrier, while a small amount of diesel or another fuel supports ignition. The concept can be interesting for converting existing engine platforms, but places high demands on control, safety, mixture formation and emission behaviour. Critical topics include ignition stability, NOx formation, pre-ignition and clean separation of the fuel paths.

H2ICE is the common English abbreviation for hydrogen internal combustion engine. It refers to a hydrogen combustion engine, not a fuel cell system. The term is frequently used in research, vehicle development and industrial decarbonization projects. For technical assessment, efficiency, NOx emissions, power density, hydrogen storage, mixture formation and operating strategy are key factors.

A hydrogen internal combustion engine is an internal combustion engine that operates with hydrogen and produces mechanical work through internal combustion. The term is often used to distinguish it from a hydrogen fuel cell. Technically relevant topics include direct injection or port fuel injection, lean combustion, high flame speed, NOx formation and abnormal combustion phenomena. Hydrogen internal combustion engines are especially interesting when existing engine and manufacturing expertise is to be reused.

Internal combustion engine development is the development of engines in which energy conversion takes place through internal combustion. It considers not only individual components, but also the interaction of combustion chamber, air path, injection, ignition, boosting, cooling and exhaust aftertreatment. A change in intake port, boost pressure or combustion chamber geometry can affect mixture formation, turbulence, combustion duration, knock tendency and efficiency at the same time. This makes the combination of simulation, testing and system understanding especially important.

A naturally aspirated engine fills its cylinders without a turbocharger or mechanical supercharger. Air enters the combustion chamber due to the intake stroke vacuum and ambient pressure. Naturally aspirated engines often provide direct response and lower air path complexity. However, their power density is limited because the maximum air mass per cycle is determined by ambient conditions and gas exchange behaviour.

A passenger car engine is an internal combustion engine for passenger vehicles. It must meet a broad range of requirements including drivability, efficiency, emissions, cost, packaging, noise behaviour and everyday usability. Modern passenger car engines are often turbocharged, hybridized and strongly influenced by emission legislation. In development, transient operation, cold start, part-load efficiency, knock resistance and thermal management are especially important.

The piston transfers combustion pressure to the crankshaft through the connecting rod. At the same time, it bounds the combustion chamber, carries the piston rings and influences charge motion, heat transfer and compression. The piston geometry, especially the crown and bowl, directly affects mixture formation and combustion. Pistons are highly loaded thermally and mechanically, so cooling, friction, weight and durability must be carefully designed.

The piston bowl is a shaped recess in the piston crown that strongly influences the combustion chamber and charge motion. It is especially used in diesel engines, hydrogen engines and direct injection concepts to control mixture formation and combustion. Bowl shape, depth, rim design and position influence swirl, tumble, spray-wall interaction, flame propagation and wall heat losses. An unfavourable piston bowl can significantly worsen emissions, efficiency, knock tendency or thermal loading.

A piston ring seals the gap between piston and cylinder wall. It reduces blow-by, controls the oil film and oil consumption, and supports heat transfer from the piston to the cylinder wall. Piston rings influence friction, emissions, wear, compression and engine durability. Their design is a compromise between good sealing, low friction losses and reliable oil management.

A racing engine is an engine developed for motorsport requirements. The main targets are usually maximum power, fast response, low weight, high engine speed and a usable power band. At the same time, thermal management, durability, knock limit, lubrication and regulations must be controlled. Simulations help design the combustion chamber, air path, exhaust system, boosting and cooling specifically for the intended racing application.

A range extender is an auxiliary unit that generates electrical energy in an electrified vehicle to increase driving range. It is often a small internal combustion engine driving a generator. Because the engine usually operates in a limited number of defined operating points, it can be strongly optimized for efficiency, noise, emissions and continuous operation. Range extender concepts are especially interesting when battery size, charging infrastructure or range requirements are critical.

Rightsizing describes the targeted design of an engine for its actual operating profile rather than simply reducing displacement. Power, torque, efficiency, emissions, cost, durability and duty cycle are evaluated together. Unlike aggressive downsizing, the engine should be efficient not only in a test cycle but also in real operation. Rightsizing is especially relevant for heavy-duty vehicles, hybrid powertrains, range extenders and alternative fuels.

A spark-ignition engine is an internal combustion engine in which the air-fuel mixture is usually ignited by a spark plug. It typically operates with gasoline, natural gas, hydrogen or other ignitable fuels. Important development parameters include spark timing, compression ratio, mixture formation, knock limit, charge motion and exhaust emissions. Compared with a diesel engine, its combustion is more strongly characterized by spark ignition, flame propagation and knock tendency.

A stationary engine is an internal combustion engine used for fixed applications rather than primarily for vehicle propulsion. Typical applications include generators, combined heat and power units, pump drives, industrial plants or emergency power systems. Stationary engines often operate for long periods at defined load points, making efficiency, durability, emissions and maintenance effort especially important. Gas engines and hydrogen engines are particularly relevant concepts in this area.

A turbocharged engine uses an exhaust gas turbocharger to compress the intake air and increase cylinder filling. This enables higher power density, engine downsizing and, in some cases, better efficiency. Developing a turbocharged engine requires careful matching of turbocharger, boost control, charge air cooling, knock limit, exhaust temperature and transient response. The interaction between 1D engine simulation, test bench work and 3D CFD in the intake and exhaust path is especially important.

A two-stroke engine completes intake, compression, power and exhaust within one crankshaft revolution. This allows more power strokes at the same engine speed than a four-stroke engine. The main challenges are scavenging, fresh charge losses, emissions, lubrication and thermal loading. Two-stroke concepts are used in small engines, certain high-performance applications and large marine diesel engines.

A valve controls gas exchange in an internal combustion engine. Intake valves open the path for fresh charge or air into the cylinder, while exhaust valves release exhaust gas. Valves must withstand high temperatures, pressure forces, accelerations and cyclic loads. Their geometry, timing and lift curve influence cylinder filling, charge motion, residual gas fraction and efficiency.