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To find more effective lean mixture preparation methods for smokeless and low NOx combustion, a numerical study of the effects of in-cylinder flow field before injection on mixture formation in a premixed compression ignition engine was conducted. Premixed compression ignition combustion is a very attractive method to reduce both NOx and soot emissions, but it still has some problems, such as high HC and CO emissions. In case of early direct injection, it is important to avoid wall wetting by spray impingement, which can cause higher HC and CO emissions. Since it is not easy to examine the effects of initial flow and injection parameters on mixture formation over the wide range by practical engine tests, a computer program named “GTT (Generalized Tank and Tube)” code was used to simulate the in-cylinder phenomena before autoignition.

Utilization of ethanol-diesel blend fuels in partial Premixed Charge Compression Ignition (PCCI) combustion was attempted to achieve clean diesel engine. The experiment was carried out using a naturally aspirated single cylinder DI diesel engine equipped with common rail injection and cooled EGR systems. PCCI combustion was realized by two stage injection in which part of fuel was injected during the compression stroke and the rest near TDC. The results indicate that under middle to high engine loads, both weak sooting tendency and low cetane number of ethanol blend fuels offer a great improvement in PM and NOx emissions when compared to the diesel combustion with ordinary pilot injection. However, this results in penalties in thermal efficiency, THC and CO emissions.

This study aims to determine strategies for improving the relations between the pressure rise rate and emissions of nitrogen oxide (NOx), hydrocarbons (HC), and carbon monoxide (CO) in low temperature combustion (LTC) operation of a diesel engine. For this purpose, an analysis was conducted on data from experiments carried out using a single-cylinder direct-injection diesel engine with variation in the injection quantity, injection timing, exhaust-gas recirculation (EGR) rate, injection pressure, injection nozzle specification and combustion chamber geometry. The results reveal that the pressure rise rate and NOx exhibit similar tendencies when varying injection timing and EGR rate, which is opposite to CO and total HC (THC) emissions, regardless of injection quantity. When the injection quantity is increased, smoke emission becomes problematic in the selection of the injection timing.

The present study aims to obtain a strategy for optimizing the combination of injection conditions and combustion chamber geometry to achieve low carbon monoxide (CO), nitrogen oxides (NOx) and smoke emissions with high thermal efficiency at low loads in direct-injection premixed charge compression ignition (DI-PCCI) operation in a diesel engine. To this end, experiments were performed using a naturally-aspirated single-cylinder DI diesel engine equipped with a common-rail injection system and a cooled exhaust gas recirculation (EGR) system under various injection conditions, including injection timing, injection angle and injection quantity, and combustion chamber geometry. The results indicate that CO emission was reduced at injection timings that provide high peak heat release rates. To improve the NOx-CO trade-off relation, the spray angle should be properly selected depending on the combustion chamber geometry.