Kitae Yeom

Effects of Exhaust Throttling on Engine Performance and Residual Gas in an SI Engine

The author would like to thank CERC (Combustion Engineering Research Center), KAIST for the financial support.

Improvement of DME HCCI Engine Performance by Fuel Injection Strategies and EGR

The authors would like to express their appreciation for financial support from Combustion Engineering Research Center (CERC) in KAIST and the Korea Energy Management Corporation (KEMCO).

Effects of Stratified EGR on the Performance of a Liquid Phase LPG Injection Engine

The authors would like to thank the Korean Ministry of Science and Technology for funding this research through national research laboratory (NRL) scheme and engineering research center (ERC) program to CERC (Combustion Engineering Research Center).

Measurements of droplet size distribution and in-cylinder mixture formation from a slit injector in a direct-injection gasoline engine

The droplet size distribution and in-cylinder mixture formation of a slit injector were investigated under varied fuel temperature and air flow conditions. This variance in fuel temperature and air flow represents the altered spray momentum and external forces acting upon the spray. Phase Doppler anemometry (PDA) was used to investigate the effect of fuel temperature and air flow on droplet size distribution. The in-cylinder mixture formation process and the factors affecting the in-cylinder mixture distribution were analyzed under various fuel temperature and air flow conditions using laser induced fluorescence (LIF). When the fuel temperature and air flow velocity increased, the smaller droplets were entrained to the upper and central parts of the spray altering the initial droplet size distribution. The reduced spray momentum decreased the spray penetration in the combustion chamber, and the interaction between the spray and piston bowl was degraded. This phenomenon eventually caused a relatively lean and dispersed mixture distribution near the spark plug at high fuel temperatures. The optimal spray momentum and external force depend on the fuel quantity (air-fuel ratio) and piston bowl shape. Consequently, the spray momentum and the external forces acting upon the spray should be optimized to form the stoichiometric and well-distributed mixture near the spark plug.

Stratified liquefied petroleum gas—dimethyl ether compression ignition engine combustion at various intake valve open timings:

Abstract The combustion and exhaust emissions characteristics of compression ignition engine with a variable valve timing device were investigated for liquefied petroleum gas (LPG) and dimethyl ether (DME) under various LPG injection timing conditions. LPG was used as the main fuel injected directly into the combustion chamber. DME was used as an ignition promoter injected into the intake port. Different LPG injection timings were tested to verify the effects of the mixture homogeneity on the combustion and exhaust emission characteristics of the LPG and DME compression ignition engine. The average charge temperature was calculated to analyse the pollutant formation. The ringing intensity was used for the analysis of knock characteristics. The combustion and exhaust emission characteristics differed significantly depending on the LPG injection and intake valve open timings. The carbon monoxide (CO) emission increased as the intake valve opened and LPG injection timings were retarded owing to the local mixture inhomogeneity. However, the particulate matter (PM) emission decreased and the nitrogen oxides (NO x ) emission increased as the intake valve open timing was retarded in the diffusion combustion regime. Finally, the combustion efficiency decreased as the intake valve open and LPG injection timings were retarded.

Effect of Inlet Temperature and CO2Concentration in the Fresh Charge on Combustion in a Homogeneous Charge Compression Ignition Engine Fuelled with Dimethyl Ether

This study focused on the effects of the CO2 gas concentration in fresh charge and induction air temperature on the combustion characteristics of homogeneous charge compression ignition with dimethyl ether (DME) fuel, which was injected at the intake port. Because of adding CO2 in fresh charge, start of auto-ignition was retarded and burn duration became longer. Indicated combustion efficiency and exhaust gas emission were found to be worse due to the incomplete combustion. Partial burn was observed at the high concentration of CO2 in fresh charge with low temperature of induction air. However, indicated thermal efficiency was improved due to increased expansion work by late ignition and prolonged burn duration. Start of auto-ignition timing was advanced with negligible change of burn duration, as induction air temperature increased. Burn duration was mainly affected by oxygen mole concentration in induction mixture. Burn duration was increased, as oxygen mole concentration was decreased.

LPG-DME Stratified Charge Compression Ignition Engine

The combustion characteristics of a liquefied petroleum gas-di-methyl ether (LPG-DME) compression ignition engine was investigated under homogeneous charge and stratified charge conditions. LPG was used as the main fuel and injected into the combustion chamber directly. DME was used as an ignition promoter and injected into the intake port. Different LPG injection timings were tested to verify the combustion characteristics of the LPG-DME compression ignition engine. The combustion was divided into three region which are homogeneous charge, stratified charge, and diffusion flame region according to the injection timing of LPG. The hydrocarbon emission of stratified charge combustion was lower than that of homogeneous charge combustion. However, the carbon monoxide and nitrogen oxide emission of stratified charge combustion were slightly higher than those of the homogeneous charge region. The indicated mean effective pressure was reduced at stratified charge region, while it was almost same level as the homogeneous charge combustion region at diffusion combustion region. The start of combustion timing of the stratified charge combustion and diffusion combustion region were advanced compared to the homogeneous charge combustion. It attributed to the higher cetane number and mixture temperature distribution which locally stratified. However, the knock intensity was varied as the homogeneity of charge was increased.