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Direct gasoline injection combined with turbo charging and down sizing is a cost effective concept to meet future requirements for emission reduction as well as increased efficiency for passenger cars. It is well known that turbulence induced by in-cylinder air motion can influence efficiency. In this study, the intake-generated flow field was varied for a direct injected turbo charged concept, with the intent to evaluate if further increase in tumble potentially could lead to higher efficiency compared to the baseline. A single cylinder head with flow separating walls in the intake ports and different restriction plates was used to allow different levels of tumble to be experimentally evaluated in a single cylinder engine. The different levels of tumble were quantified by flow rig experiments.

Future demands for improvements in the fuel economy of gasoline passenger car engines will require the development and implementation of advanced combustion strategies, to replace, or combine with the conventional spark ignition strategy. One possible strategy is homogeneous charge compression ignition (HCCI) achieved using negative valve overlap (NVO). However, several issues need to be addressed before this combustion strategy can be fully implemented in a production vehicle, one being to increase the upper load limit. One constraint at high loads is the combustion becoming too rapid, leading to excessive pressure-rise rates and large pressure fluctuations (ringing), causing noise. In this work, efforts were made to reduce these pressure fluctuations by using a late injection during the later part of the compression. A more appropriate acronym than HCCI for such combustion is SCCI (Stratified Charge Compression Ignition).

Future requirements for emission reduction from combustion engines in ground vehicles might be met by using the HCCI combustion concept. In this study, negative valve overlap (NVO) and low lift, short duration, camshaft profiles, were used to initiate HCCI combustion by increasing the internal exhaust gas recirculation (EGR) and thus retaining sufficient thermal energy for chemical reactions to occur when a pilot injection was introduced prior to TDC, during the NVO. One of the crucial parameters to control in HCCI combustion is the combustion phasing and one way of doing this is to vary the relative ratio of fuel injected in pilot and main injections. The combustion phasing is also influenced by the total amount of fuel supplied to the engine, the combustion phasing is thus affected when the load is changed. This study focuses on the reactions that occur in the highly diluted environment during the NVO when load and pilot to main ratio are changed.

This work evaluates the effect of charge stratification on combustion phasing, rate of heat release and emissions for HCCI combustion. Engine experiments in both optical and traditional single cylinder engines were carried out with PRF50 as fuel. The amount of stratification as well as injection timing of the stratified charge was varied. It was found that a stratified charge can influence combustion phasing, increasing the stratification amount or late injection timing of the stratified charge leads to an advanced CA50 timing. The NOx emissions follows the CA50 advancement, advanced CA50 timing leads to higher NOx emissions. Correlation between CA50 can also be seen for HC and CO emissions when the injection timing was varied, late injection and thereby advanced CA50 timing leads to both lower HC and CO emissions.