Heechang Oh

The Effect of Multi-ignition Strategy on the Combustion and Emission Characteristics in a Ultra Lean Burn GDI Engine

Since air pollution problem by emissions from automotive vehicles has become social issues, lean-burn gasoline direct injection (GDI) engine is focused as an alternative to meet the requirement of reinforced emission regulation and improved fuel consumption. Spray-guided type DI combustion is promising technology, which characterized by the centrally mounted injector and closely positioned spark plug, since stable lean combustion can be realized even at ultra-lean mixture condition. In the present study, the effect of multi-ignition with developed charge coil on combustion and emission characteristics was investigated in optical accessible single cylinder engine. In order to fully understand the in-cylinder phenomena and the mechanisms of emission production, optical diagnostics, such as flame visualization was also carried out at frequently using operating condition. Multi-ignition is effective to improve fuel economy but increase NOx emission at flammability limit.

Combustion Characteristics of Stratified Mixture in Lean-Burn LPG Direct-Injection Engine With Spray-Guided Combustion System

Today, we are faced with the problems of global warming and fossil fuel depletion, and they have led to the enforcement of new emissions regulations. Direct-injection spark-ignition engines are a very promising technology that can comply with the new regulations. These engines offer the advantages of better fuel economy and lower emissions than conventional port-injection engines. The use of LPG as the fuel reduces carbon emissions because of its vaporization characteristics and the fact that it has lower carbon content than gasoline. An experimental study was carried out to investigate the combustion process and emission characteristics of a 2-liter spray-guided LPG direct-injection engine under lean operating conditions. The engine was operated at a constant speed of 2000 rpm under 0.2-MPa brake mean effective pressure, which corresponds to a common operation point of a passenger vehicle. Combustion stability, which is the most important component of engine performance, is closely related to the operation strategy and it significantly influences the degree of fuel consumption reduction. In order to achieve stable combustion with a stratified LPG mixture, an inter-injection spark ignition (ISI) strategy, which is an alternative control strategy to two-stage injection, was employed. The effects of the compression ratio on fuel economy were also assessed; due to the characteristics of the stratified LPG mixture, the fuel consumption did not reduce when the compression ratio was increased.© 2014 ASME

LPG Spray Characteristics in a Multi-hole Injector for Gasoline Direct Injection

Abstract Liquefied petroleum gas (LPG) is regarded as an alternative fuel for spark ignition engine due to similar or even higheroctane number. In addition, LPG has better fuel characteristics including high vaporization characteristic and low carbon/hydrogen ratio leading to a reduction in carbon dioxide emission. Recently, development of LPG direct injection systemstarted to improve performance of vehicles fuelled with LPG. However, spray characteristics of LPG were not well under-stood, which is should be known to develop injector for LPG direct injection engines. In this study, effects of operation con-dition including ambient pressure, temperature, and injection pressure on spray properties of n-butane were evaluated andcompared to gasoline in a multi-hole injector. As general characteristics of both fuels, spray penetration becomes smaller withan increase of ambient pressure as well as a reduction in the injection pressure. However, it is found that evaporation of n-butane was faster compared to gasoline under all experimental condition. As a result, spray penetration of n-butane wasshorter than that of gasoline. This result was due to higher vapor pressure and lower boiling point of n-butane. On the otherhand, spray angle of both fuels do not vary much except under high ambient temperature conditions. Furthermore, sprayshape of n-butane spray becomes completely different from that of gasoline at high ambient temperature conditions due toflash boiling of n-butane.

Combustion process and PM emission characteristics in a stratified DISI engine under low load condition

ABSTRACT An experimental study was carried out to investigate the combustion process and particulate matter (PM) emission characteristics in a spray guided direct injection spark ignition (DISI) engine under lean-stratified operation. In-cylinder pressure analysis, PM emission measurement, and visualization of the in-cylinder combustion were applied. Heat release rate during stratified combustion showed 2-staged combustion characteristics. The main combustion was preceded with fast combustion speed and high peak of heat release rate. Combustion process after the main combustion showed longer combustion duration and relatively lower intensity of heat release rate. Propagation of non-luminous blue flame was observed during the early stage of the main combustion process. Mixing controlled combustion with luminous sooting flame development was observed during the late stage of the main combustion. Lastly, non-luminous blue flame was dominant during the secondary combustion process, which was interpreted as the combustion of the unburned lean-homogeneous mixture. PM emission characteristics were investigated under various injection timing conditions. The number and total weight of PM emission were increased as the injection timing was retarded. These trends were coincident with the trend of sooting flame luminosity during the combustion process with variation of injection timing. PM emission and mixing controlled combustion were found to have mainly originated from the inhomogeneous gas phase distribution of the stratified mixture.