• Journal of Institute of Convergence Technology
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• v.9 no.1
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• pp.13-19
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• 2019

The purpose of this study is to suggest a new method to determine a combustion phase (start of combustion and end of combustion) using a combustion pressure data. Unlike previous research method that used heat release amount, the difference between the combustion pressure measured in the combustion chamber and the motoring pressure was used to determine the combustion phase. This research was conducted using a single-cylinder diesel engine with a compression ratio of 17.7. The test was conducted under various injection timing. The newly proposed method showed high accuracy in combustion mode with early injection, as well as the conventional combustion mode. It is expected that this method will be used to study new combustion strategies such as HCCI (homogeneous charge compression ignition) and RCCI (reactivity controlled compression ignition) that are applying early injection strategies as well as existing combustion modes.

• International Journal of Automotive Technology
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• v.8 no.4
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• pp.395-402
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• 2007

Homogeneous Charge Compression Ignition (HCCI) shows great potential for low $NO_x$ emission but is hampered by the problem of no direct method to control the combustion process. Therefore, HCCI combustion becomes unstable easily, especially at lower and higher engine load. This paper presents a method to achieve diesel-fueled HCCI combustion, which involves directly injecting diesel fuel into the cylinder before the piston arrives at top dead center in the exhaust stroke and adjusting the valve overlap duration to trap more high temperature residual gas in the cylinder. The combustion stability of diesel-fueled HCCI combustion and the effects of engine load, speed, and valve overlap on it are the main points of investigation. The results show that: diesel-fueled HCCI combustion has two-stage heat release rate (low temperature and high temperature heat release) and very low $NO_x$ emission, combustion stability of the HCCI engine is worse at lower load because of misfire and at higher load because of knock, the increase in engine speed aids combustion stability at lower load because the heat loss is reduced, and increasing negative valve overlap can increase in-cylinder temperature which aids combustion stability at lower load but harms it at higher load.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.4
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• pp.182-189
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• 2005

In order to investigate the effect of premixed gasoline, diesel fuel, and n-heptane charges on the combustion and exhaust emission characteristics in a direct injection (DI) diesel engine, the experimental studies are performed. The premixed fuels are injected into the premixing chamber that installed upstream of the intake port in order to minimize the inhomogeneity effect of premixed charge. The injection nozzle for directly injected fuel is equipped in the center of the combustion chamber. The air temperature control system is equipped in the intake manifold to examine the effect of air temperature. The experimental results of this study show premixing fuel is effective method to reduce the NOx and soot emissions of diesel engine. NOx emissions are linearly decreased with increasing premixed ratio for the three kinds of premixed fuels. The heating of intake air $(80^{\circ}C)$ reduced the deterioration of BSFC in high premixed ratio, because it promotes evaporation of premixed diesel droplet in the premixing chamber.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.5
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• pp.449-456
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• 2010

The HCCI engine is a prospective internal combustion engine with which high diesel-like efficiencies and very low NOx and particulate emissions can be achieved. However, several technical issues must be resolved before HCCI engines can be used for different applications. One of the issues concerning the HCCI engine is that the operating range of this engine is limited by the rapid pressure rise caused by the release of excessive heat. This heat release is because of the self-accelerated combustion reaction occurring in the engine and the resulting engine knock in the high-load region. The purpose of this study is to evaluate the role of thermal stratification and fuel stratification in reducing the pressure rise rate in an HCCI engine. The concentrations of NOx and CO in the exhaust gas are also evaluated to confirm combustion completeness and NOx emission. The computation is carried out with the help of a multizone code, by using the information on the detailed chemical kinetics and the effect of thermal and fuel stratification on the onset of ignition and rate of combustion. The engine is fueled with dimethyl ether (DME), which allows heat release to occur in two stages, as opposed to methane, which allows for heat release in a single stage.

• 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.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.1
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• pp.39-47
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• 2004

The objective of this study is to analyse the spray characteristics according to the injection duration under ambient pressure condition and to investigate the relationship between vorticity and entropy for controlling diffusion process that is the most important thing during the intake stroke injection process. Therefore, the spray velocity was obtained by using the PIV method that has been an useful optical diagnostics technology, and vorticity calculated from spray velocity component with vorticity algorithm. In addition, the homogeneous diffusion rate of spray was quantified by using the entropy analysis based on the Boltzmann's statistical thermodynamics. From these method, we found that as injection duration increases, spray velocity increases and the location of vortex is moved to the downstream of spray. In the same condition, as the entropy decrease, mean vorticity increases. This means that the concentration of spray droplets caused by the increase of injection duration is more effective than the increase of momentum dissipation.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.5
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• pp.25-31
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• 2006

Controlled Auto Ignition(CAI) combustion has great potential in achieving significant increase in engine efficiency, while simultaneously reducing exhaust emissions. The process itself involves the auto ignition and subsequent simultaneous combustion of a premixed charge. In this study, NVO(Negative Valve Overlap) system was applied to a CAI engine in order to use residual gas. The fuel was injected directly to the cylinder under the high temperature condition resulting from heating the intake port to initiate CAI combustion. This paper introduced the valve timing strategy and experimental set-up. From this study, the effect of engine speed and valve timing on CAI combustion and exhaust emissions was clarified. In addition, stratified charge method was used to extend CAI operating region.

• Journal of the Korean Institute of Gas
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• v.13 no.6
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• pp.21-28
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• 2009

The purpose of this study is to gain a better understanding of the effects of thermal stratification and partial fuel stratification on reducing the pressure-rise rate and emission in HCCI combustion. The engine is fueled with Di-Methyl Ether(DME) which has unique 2-stage heat release. Computational work is conducted with multi-zones model and detailed chemical reaction scheme. Calculation result shows that wider thermal stratification and partial fuel stratification prolong combustion duration and reduce pressure rise rate. But too wide partial fuel stratification increases CO and NOx concentration in exhaust gas, and decreases combustion efficiency.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.2
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• pp.83-90
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• 2014

The main purpose of the study is to investigate the ideal manner and ratio to inject gasoline and DME simultaneously into intake port, and moreover to confirm the characteristics of combustion and emission of engine. Experimental conditions are 1200 rpm, compression ratio 8.5, intake air temperature (383 K). Internal cylinder pressure was collected to confirm the characteristics of combustion in order to calculate the heat release rate in the cylinder. In addition, HORIBA (MEXA 7100) which was possible analyzing emissions (NOx, CO, HC) was used. Vanguard gasoline engine (23HP386447) was used in this experiment. The result show that fuel design (DME-Gasoline) leads to the decrease of low temperature heat release, which is a benefit for higher-load on the HCCI engine. Also, IMEP and the indicated thermal efficiency increase with combustion-phasing retard, and these observations can be explained by considering the control of low temperature oxidation of DME.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1401-1406
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• 2004

In this paper, we present the theoretical and numerical results of scavenge characteristics in a small prechamber of an HCCI(Homogeneous Charge Compression Ignition) engine. Two theoretical models are proposed in prediction of the scavenge time and the efficiency ; one is the non-mixing models in which it is assumed that the input gas($CH_{4}$) and the existing gas(air) do not mix with each other, and the other is the fully-mixed model in which the two gases are assumed to mix completely before ejecting to the ambient air. Focus is also given to the effect on the scavenge performance of the size of the chamber oulet.