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Emissions remain a critical issue affecting engine design and operation, while energy conservation is becoming increasingly important. One approach to favorably address these issues is to achieve homogeneous charge combustion and stratified charge combustion at lower peak temperatures with a variable compression ratio, a variable intake temperature and a trapped rate of the EGR using NVO (negative valve overlap). This experiment was attempted to investigate the origins of these lower temperature auto-ignition phenomena with SCCI and CAI using gasoline fuel. In case of SCCI, the combustion and emission characteristics of gasoline-fueled stratified-charge compression ignition (SCCI) engine according to intake temperature and compression ratio was examined. We investigated the effects of relative air/fuel ratio, residual EGR rate and injection timing on the CAI combustion area.

As the exhaustion of petroleum resources and air pollution problems are getting more serious day by day, demands for low emission levels and higher thermal efficiency of vehicle engines have been increased. In light of this, the diesel engine has many advantages such as high thermal efficiency, a cheaper price of fuel, and what is more it has a low CO2 exhaustion level well known as the factor of ‘Global Warming’, therefore the use of diesel engines is getting increased. However in the case of diesel engine, NOx increases in the local high temperature region, and particulate matter increases in fuel rich regions. That is why, getting down the peak temperature to reduce NOx emission and making better air-fuel mixing to minimize particulate matter formation are required and Homogeneous Charge Compression Ignition (HCCI) is a technique which can make those conditions.

Owing to the presence of oxygen atoms in biodiesel, the use of this fuel in compression ignition (CI) engines has the advantage of reducing engine-out harmful emissions. In this context, biodiesel fuel can also be used to extend the low temperature combustion (LTC) regime because it inherently suppresses soot formation within the combustion chamber. Therefore, in this study, LTC characteristics of biodiesel were investigated in a single cylinder CI engine; the engine performance and emission characteristics with biodiesel and conventional petro-diesel fuels were evaluated and compared. A modulated kinetics (MK)-like approach was employed to realize LTC operation. The engine test results showed that LTC operation was achieved by retardation of the fuel injection timing. The results also showed that using biodiesel reduced smoke, THC, and CO emissions but increased NOx emissions.