• Transactions of the Korean hydrogen and new energy society
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• v.22 no.6
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• pp.895-904
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• 2011

Stratified charge has been thought as one of the ways to avoid a sharp pressure rise on HCCI combustion. The purpose of this study is to evaluate the potential of stratified charge for reducing PRR on HCCI combustion. The pre-mixture with thermal, mixing and EGR stratifications is charged in Rapid Compression Machine. After that, the pre-mixture is compressed and in that process, in-cylinder gas pressure and temperature are analyzed. Additionally numerical calculation with multi-zones modeling is run to know the potential of stratified charge for reducing PRR.

• Journal of the Korean Institute of Gas
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• v.14 no.6
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• pp.7-14
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• 2010

This study investigated the effect on reducing the pressure rise rate(PRR) in HCCI Engine by the variation of mixing ratio in the pre-mixture of DME and n-Butane that has different auto-ignition characteristics. In addition to measure of gas pressure in the engine cylinder, chemiluminescence image using the optical accessible engine and numerical analysis with multi-zones model were used to assess the combustion at each local area in the combustion chamber. The maximum PRR changes depending on mixing condition of DME and n-Butane. When DME is stratified and n-Butane is distributed uniformly, maximum PRR becomes lowest which is about 0.25MPa/ms and it corresponds to 5deg. retarding of CA50.

• Journal of IKEEE
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• v.15 no.4
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• pp.305-312
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• 2011

A primary interest of this work is to develop an efficient and powerful repetitive pulser system for the application of ultra wide band generation. The important component of the pulser system is a small-sized coaxial type spark gap with planar electrodes filled with SF6 gas. A repetitive switching action by the coaxial spark gap generates two consecutive pulses in less than a microsecond with rise times of a few hundred picoseconds (ps). A set of several parameters for the repetitive switching of the spark gap is required to be optimized in charging and discharging systems of the pulser. The parameters in the charging system include a circuit scheme, circuit elements, the applied voltage and current ratings from power supplies. The parameters in the discharging system include the spark gap geometry, electrode gap distance, gas type, gas pressure and the load. The characteristics of the spark gap discharge, such as breakdown voltage, output current pulse and recovery rate are too dynamic to control by switching continuously at a high pulse repetition rate (PRR). This leads to a low charging efficiency of the spark gap system. The breakthrough of the low charging efficiency is achieved by a parallel operation of two spark gaps system. The operational behavior of the two spark gaps system is presented in this paper. The work has focused on improvement of the charging efficiency by scaling the PRR of each spark gap in the two spark gaps system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.6
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• pp.451-464
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• 2014

This study used numerical methods to investigates investigate the exhaust gas recirculation (EGR) effect under the condition of boost pressure condition on a homogeneous charge compression ignition (HCCI) combustion engine using numerical methods. The detailed chemical-kinetic mechanisms and thermodynamic parameters for n-heptane, iso-octane, and PRF50 from the Lawrence Livermore National Laboratory (LLNL) are were used for this study. The combustion phase affects the efficiency and power. To exclude these effects, this study decided to maintain a 50 burn point (CA50) at 5 CA after top dead center aTDC. The results showed that the EGR increased, but the low temperature heat release (LTHR), negative temperature coefficient (NTC), and high temperature heat release (HTHR) were weakened due by theto effect of the O2 reduction. The combined EGR and boost pressure enhanced the autoignition reactivity, Hhence, the LTHR, NTC, and HTHR were enhanced, and the heat-release rate was increased. also In addition, EGR decraeased the indicated mean effective pressure (IMEP), but the combined EGR and boost pressure increased the IMEP. As a results, combining the ed EGR and boost pressure was effective to at increase increasing the IMEP and maintaining the a low PRR.