Yonggyu Lee

Effect of Intake Pressure on Emissions and Performance in Low Temperature Combustion Operation of a Diesel Engine

One of the effective ways to reduce both NOx and PM at the same time in a diesel CI engine is to operate the engine in low temperature combustion (LTC) regimes. In general, two strategies are used to realize the LTC operation-dilution controlled LTC and late injection LTC - and in this study, the former approach was used. In the dilution controlled regime, LTC is achieved by supplying a large amount of EGR to the cylinder. The significant EGR gas increases the heat capacity of in-cylinder charge mixture while decreasing oxygen concentration of the charge, activating low temperature oxidation reaction and lowering PM and NO x emissions. However, use of high EGR levels also deteriorates combustion efficiency and engine power output. Therefore, it is widely considered to use increased intake pressure as a way to resolve this issue. In this study, the effects of intake pressure variations on performance and emission characteristics of a single cylinder diesel engine operated in LTC regimes were examined. LTC operation was achieved in less than 8% O 2 concentration and thus a simultaneous reduction of both PM and NOx emission was confirmed. As intake pressure increased, combustion efficiency was improved so that THC and CO emissions were decreased. A shift of the peak Soot location was also observed to lower O2 concentration while NOx levels were kept nearly zero. In addition, an elevation of intake pressure enhanced engine power output as well as indicated thermal efficiency in LTC regimes. All these results suggested that LTC operation range can be extended and emissions can be further reduced by adjusting intake pressure.

Modeling of Engine Coolant Temperature in Diesel Engines for the Series Hybrid Powertrain System

Modeling of engine coolant temperature was conducted for a series hybrid powertrain system. The purpose of this modeling was a simplification of complex heat transfer process inside a engine cooling system in order to apply it to the vehicle powertrain simulation software. A basic modeling concept is based on the energy conservation equation within engine coolant circuit and are composed of heat rejection from engine to coolant, convection heat transfer from an engine surface and a radiator to ambient air. At the final stage, the coolant temperature was summarized as a simple differential equation. Unknown heat transfer coefficients and heat rejection term were defined by theoretical and experimental methods. The calculation result from this modeling showed a reasonable prediction by comparison with the experimental data.

Effect of Injection Pressure on Low Temperature Combustion in CI Engines

Diesel low temperature combustion (LTC) is the concept where fuel is burned at a low temperature oxidation regime so that NOx and particulate matters (PM) can simultaneously be reduced. There are two ways to realize low temperature combustion in compression ignition engines. One is to supply a large amount of EGR gas combined with advanced fuel injection timing. The other is to use a moderate level of EGR with fuel injection at near TDC which is generally called Modulated kinetics (MK) method. In this study, the effects of fuel injection pressure on performance and emissions of a single cylinder engine were evaluated using the latter approach. The engine test results show that MK operations were successfully achieved over a range of with 950 to 1050 bar in injection pressure with 16% O2 concentration, and NOx and PM were significantly suppressed at the same time. In addition, with an increase in fuel injection pressure, the levels of smoke, THC and CO were decreased while NOx emissions were increased. Moreover, as fuel injection timing retarded to TDC, more THC and CO emissions were generated, but smoke and NOx were decreased.

Experimental Study on the Performance Characteristics of Air Hybrid Engine

A preliminary experimental study of new concept air hybrid engine, which stores compressed air in the tank during braking and re-use it to propel vehicle during crusing or acceleration, was carried out in this study. A single cylinder engine was modified to realize the concept of air hybrid engine. Independent variable valve lift system was adopted in one of the exhaust valves to store the compressed air into the air tank during compression period. An air injector module was installed in the place of spark plug, and the stored compressed air was supplied during the expansion period to realize air motoring mode. For air compression mode, the tank with volume of 30 liter could be charged up to more than 13 bar. By utilizing this stored compressed air, motoring work of 0.41 bar of IMEP(Indicated mean effective pressure) at maximum can be generated at the 800rpm conditions, which is higher than the case of normal idle condition by 1.1 bar of IMEP.

Fuel Stratification in a Liquid-Phase LPG Injection Engine

The authors would like to thanks the Korean Ministry of Science and Technology for funding this research through national laboratory (NRL) project and the Korean Ministry of Environment for funding this work through ECO-21 project.