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Engines with gasoline direct injection promise an increase in efficiency mainly due to the overall lean mixture and reduced pumping losses at part load. But the near stoichiometric combustion of the stratified mixture with high combustion temperature leads to high NOx emissions. The need for expensive lean NOx catalysts in combination with complex operation strategies may reduce the advantages in efficiency significantly. The Bowl-Prechamber-Ignition (BPI) concept with flame jet ignition was developed to ignite premixed lean mixtures in DISI engines. The mainly homogeneous lean mixture leads to low combustion temperatures and subsequently to low NOx emissions. By additional EGR a further reduction of the combustion temperature is achievable. The BPI concept is realized by a prechamber spark plug and a piston bowl. The main feature of the concept is its dual injection strategy.

In this work, heat loss was investigated in two different HCCI single cylinder engines. Thermocouples were adapted to the surfaces of the cylinder heads and the temperature oscillations were detected in a wide range of the engine operation maps. The resultant heat transfer profiles were compared to the heat losses predicted by existing models. As major discrepancies were stated, a new phenomenological model was developed that is well-manageable and describes the heat loss in HCCI mode more precisely than existing models. To analyze the insulating effect of deposits, the heat transfer equation was solved analytically by an approach that allows consideration of multiple layers with different material properties and thickness. This approach was used for the first time in conjunction with engines to calculate the heat flux at the surface of deposits and the deposit thickness.

For spark ignition engines, the most effective way to reduce the overall fuel consumption and CO2 emissions respectively is the implementation of gasoline direct injection technology. In comparison to the current wall and air guided systems, the direct injection system of the second generation - the spray guided DI- is the most promising one with respect to fuel economy and emission. In order to exploit its full potential, a thorough combustion process development regarding injector and spark plug design and their positioning within the combustion chamber is essential. Especially multihole injectors offer many degrees of freedom with regard to the nozzle shape and spray pattern. To reduce the development work and costs necessary to identify the ideal nozzle characteristic and spray pattern, reliable CFD models are necessary.

The California LEV1 II program will be introduced in the year 2003 and requires a further reduction of the exhaust emissions of passenger cars. The cold start emissions represent the main part of the total emissions of the FTP2-Cycle. Cold start emissions can be efficiently reduced by injecting secondary air (SA) in the exhaust port making compliance with the most stringent standards possible. The thermochemical conditions (mixing rate and temperature of secondary air and exhaust gas, exhaust gas composition, etc) prevailing in the exhaust system are described in this paper. This provides knowledge of the conditions for auto ignition of the mixture within the exhaust manifold. The thus established exothermal reaction (exhaust gas post-combustion) results in a shorter time to light-off temperature of the catalyst. The mechanisms of this combustion are studied at different engine idle conditions.

In this study different methods to reduce the soot emissions of Diesel engines were investigated and compared to obtain their soot reduction potential. Apart from investigations on the practically usable engine map area with so called homogeneous charge compression ignition (HCCI) combustion processes a new heterogeneous combustion processes was developed and investigated which offers significantly reduced soot emissions while still applicable in the entire engine map. For the HCCI experiments the emphasis was put on the achievable engine load range when using conventional injector nozzles which still allow a conventional heterogeneous engine operation.

Advanced thermal management systems in passenger cars present a possibility to increase efficiency of current and future vehicles. However, a vehicle integrated thermal management of the combustion engine is essential to optimize the overall thermal system. This paper shows results of an experimental heat flux analysis of a state-of-the-art automotive diesel engine with common rail injection, map-controlled thermostat and split cooling system. Measurements on a climatic chamber engine test bench were performed to investigate heat fluxes and energy balance in steady-state operation and during engine warm-up from different engine start temperatures. The analysis includes the influence of the operating point and operating parameters like EGR rate, injection strategy and coolant temperature on the engine energy balance.

The two-stroke SI engine is the predominant driving unit in applications that require a high power-to-weight ratio, such as handheld power tools. Regarding the latest regulations in emission limits the main development area is clearly a further reduction of the exhaust emissions. The emissions are directly linked to the combustion processes and the scavenging losses. The optimization of the combustion processes, which represents one of the most challenging fields of research, is still one of the most important keys to enhance the thermal efficiency and reduce exhaust emissions. Regarding future emission regulations for small two-stroke SI engines it is inevitable that the emissions of gases causing the greenhouse effect, like carbon dioxide, need to be reduced. As most small SI engines are carburetted and operate open loop, the mixture formation and the amount of residual gas differs from cycle to cycle [1].

Diesel engines face difficult challenges with respect to engine-out emissions, efficiency and power density as the legal requirements concerning emissions and fuel consumption are constantly increasing. In general, for a diesel engine to achieve low raw emissions a well-mixed fuel-air mixture, burning at low combustion temperatures, is necessary. Highly premixed diesel combustion is a feasible way to reduce the smoke emissions to very low levels compared to conventional diesel combustion. In order to reach both, very low NOX and soot emissions, high rates of cooled EGR are necessary. With high rates of cooled EGR the NOX formation can be suppressed almost completely. This paper investigates to what extent the trade-off between emissions, fuel consumption and power of a diesel engine can be resolved by highly premixed and low temperature diesel combustion using injection nozzles with reduced injection hole diameters and high pressure fuel injection.

High frequency ignition (HFI) and conventional transistor coil ignition (TCI) were investigated with an optically accessible single-cylinder research engine to gain fundamental understanding of the chemical reactions taking place prior to the onset of combustion. Instead of generating heat in the gap of a conventional spark plug, a high frequency / high voltage electric field is employed in HFI to form chemical radicals. It is generated using a resonant circuit and sharp metallic tips placed in the combustion chamber. The setup is optimized to cause a so-called corona discharge in which highly energized channels (streamers) are created while avoiding a spark discharge. At a certain energy the number of ionized hydrocarbon molecules becomes sufficient to initiate self-sustained combustion. HFI enables engine operation with highly diluted (by air or EGR) gasoline-air mixtures or at high boost levels due to the lower voltage required.

In this work the formation and oxidation of soot inside a direct injection spark ignition engine at different injection and ignition timing was investigated. In order to get two-dimensional data during the expansion stroke, the RAYLIX-technique was applied in the combustion chamber of an optical accessible single cylinder engine. This technique is a combination of Rayleigh-scattering, laser-induced incandescence (LII) and extinction which enables simultaneous measurements of temporally and spatially resolved soot concentration, mean particle radii and number densities. These first investigations show that the most important source for soot formation during combustion are pool fires, i.e. liquid fuel burning on the top of the piston. These pool fires were observed under almost all experimental conditions.

Controlled Autoignition (CAI) is a very promising technology for simultaneous reduction of fuel consumption and engine-out emissions [3, 4, 9, 16]. But the operating range of this combustion mode is limited on the one hand by high pressure gradients with the subsequent occurrence of knocking, increasing NOX-emissions and cyclic variations, and on the other hand by limited operating stability due to low mixture temperatures. At higher loads the required amount of internal EGR decrease to reach self-ignition conditions decrease and hence the influence of the ignition spark gain. The timing of the ignition spark highly influence the combustion process at higher loads. With the ignition spark, pre-reactions are initialized with a defined heat release. Thus the location of inflammation and flame propagation can be strongly influenced and cyclic variations at higher loads can be reduced.

In this work, heat loss was investigated in two different HCCI single cylinder engines. Thermocouples were adapted to the surfaces of the cylinder heads and the temperature oscillations were detected in a wide range of the engine operation conditions. The local heat transfer is analyzed with port fuel and direct injection, for different engine parameters and operating points. It is shown that the spatially averaged measured heat loss in HCCI operation represents the global heat loss well. The spatial variations are small in the operation map presuming stable operating points with low cyclic variations and good engine performance. Furthermore, the heat loss measured in HCCI operation is compared to the heat loss detected in homogeneous and stratified DI-SI operation in the same engine. It is shown that the local heat losses in stratified DI-SI operation show large variations, depending on the direction of the flame propagation.

The European Union (EU) has defined legally-binding targets for the fleet of new cars allowing 95 grams CO2 per kilometer in 2021. It is already under discussion to reduce average emissions of the EU car fleet by further 15% in 2025 and again by 30% in 2030 compared to 2021 goal. Therefore, improvement of fuel economy is becoming one of the most important issues for the car manufacturers. Today’s conventional car powertrain systems are reaching their technical limits and will not be able to meet future fuel economy targets without further development of additional measures. This paper presents the analysis of a Rankine cycle unit applied to improve the overall efficiency of a hybrid electric vehicle (HEV). The authors propose a new concept for recovering a considerable part of exhaust waste heat from an HEV with spark ignition internal combustion engine (ICE) by applying a bottoming Rankine cycle with a Ruths storage tank.

In this paper, results of experimental and numerical investigations of stratified exhaust gas recirculation in a single-cylinder gasoline engine are presented. The engine was operated in spray guided direct injection mode. The radial exhaust gas stratification was achieved by a spatial and temporal separated intake of exhaust gas and fresh air. The spatial separation of both fluids was realized by specially shaped baffles in the inlet ports, which prevent an early mixing up to the inlet valves. The temporally separation was performed by impulse charge valves, with one for the fresh air and one for the exhaust gas. From various possible strategies for time-dependent intake of fresh air and exhaust gas, four different strategies for the exhaust gas stratification were examined.

Spark ignited engines with direct injection (DISI) in fuel stratified mode promise an increase in efficiency mainly due to reduced pumping losses at part load. However, the need for expensive lean NOx catalysts may reduce this advantage. Therefore, a Bowl-Prechamber-Ignition (BPI) concept with flame jet ignition was developed to ignite premixed lean mixtures in DISI engines. It is characterised by a combination of a prechamber spark plug and a piston bowl. An important feature of the concept is its dual injection strategy. A pre injection in the inlet stroke produces a homogeneous lean mixture with an air fuel ratio of λ = 1.5 to λ = 1.7. A second injection with a small quantity of fuel is directed towards the piston bowl during the compression stroke. The enriched air fuel mixture of the piston bowl is transported by the pressure difference between main combustion chamber and prechamber into the prechamber.