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In present days, most of researches concerned with vehicle engines have been performed to reduce vehicle emissions and to improve engine efficiency. For the requirements, LPG (Liquefied Petroleum Gas) engine which has lots of advantages such as low emission level, cheaper fuel cost and enough infrastructures has had lots of interest as an alternative fuel engine. What is more, it has a low emission level of CO2 well-known as the factor of ‘Global Warming’, thus the use of LPG engines has been increased. Especially since MPI(Multi Point Injection) type LPLi(Liquid Phase LPG injection) system was used for the fuel supply system, disadvantages of LPG engine such as low engine performance, decreased charging efficiency and cold starting difficulty have been improved and prejudices against LPG engines have been changed a lot. In light of this, the motion to use LPLi engines instead of diesel engines has been increasing.

Automotive manufacturers and engineers have paid attention to promoting engine performance with low emissions satisfying many emission regulations. With such goals in mind, we have investigated new cooling strategies such as high coolant temperature control, fast warm-up and post cooling using an automotive cooling system controlled by electronic actuators. The cooling system in a 2.7 liter HSDI engine was modified for the purpose of this study, and an engine experiment was carried out on a New European Drive Cycle (NEDC). The conventional water pump was decoupled from the engine and electronically controlled by a BLDC motor. Valves were installed at the coolant pathways between the engine and cooling components. Overall, this modification led to a reduction in both fuel consumption and exhaust gas emissions (e.g. THC, CO). The reduction was particularly considerable at the low speed and low load-drive conditions by controlling high temperature of the coolant.

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.

Since environmental problems are getting serious, the worldwide are focused on exhaust emission from the vehicle. Many researchers have been performed to solve these problems in many ways. In this paper, we tried to reduce the emission by improving the traditional mechanical engine cooling systems which control the engine temperature with only engine speed and thermostat. The paper explained the improvement of emission by cooling system which is controlled by an electronic system based on the engine status.

The effects of tumble flow generated by various intake ports on the lean burn characteristics in a four-valve pentroof engine were investigated. Tumble intensities were tested for three intake ports of different entry angle; 25°, 20° and 15°. The flow characteristics in cylinder were measured under motored conditions with laser Doppler velocimetry. The lean burn performances were examined in an operating 4-cylinder engine. The combustion duration under lean mixture conditions were calculated by heat release analysis of the pressure trace. The flame developments in a single-cylinder optical engine were visualized with an image-intensified CCD camera to see the effect of different flow patterns with three inlet ports of strong and weak tumble. It was found that there is a correlation between the stronger tumble during induction and the higher convective velocity and turbulence levels at the time of ignition, which result in faster and stable combustion under lean mixture conditions.

Combinations of swirl flow and tumble flow generated by 13 types of swirl control valve were tested by using both impulse steady flow rig and LDV. Comparison between the steady flow characteristics and the result of LDV measurement under motoring condition shows that tumble flow generates turbulence in combustion chamber more effectively than swirl flow does, and that swirling motion reduces the cycle by cycle variation of mean velocity in combustion chamber which tends to be generated by tumbling motion. Performance tests are also carried out under the condition of homogeneous charge. Tumble flow promotes the combustion speed more strongly than expected from its turbulence intensity measured by LDV. It is also shown that lean limit air fuel ratio does not have a strong relation with cycle variation of mean velocity but with turbulence intensity.