• 대한안전경영과학회:학술대회논문집
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• 대한안전경영과학회 2009년도 추계학술대회
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• pp.223-229
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• 2009

The engine backfire leading to the damage to the intake system is observed in the mixer-type LPG engines. The hot spot flowing back into the intake manifold from the engine cylinder during the valve overlap period is known to give rise to the backfire. This backfire is known to be the main cause of the abrupt stop of the vehicle leading to the accidents on the streets. In this study, the cylinder pressure buildup at the later stage of combustion due to the prolonged burning is presumed to be the main cause of the backflow leading to the backfire. This is experimentally observed by creating the engine misfire using the ill-conditioned ignition systems.

• 한국자동차공학회논문집
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• 제22권4호
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• pp.121-130
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• 2014

This paper is the second investigation on the effects of intake flow control methods on the part load performance in a spark ignition engine. In the previous work, two control methods, port throttling and masking, were compared with respect to lean misfire limit, fuel consumption and emissions. In this work, the effects of these two methods on EGR characteristics were studied and simultaneously the differences between EGR and lean combustion as a dilution method were investigated. The results show that EGR limit is expanded up to 23% and 3 ~ 5% improvement in the fuel consumption are achieved around 8 ~ 13% rates by the flow controls comparing with 10% limit and 1.5% reduction around 3% rate of non-control case. The masking method is more effective on the limit expansion than throttling as like as lean misfire limit; however there is no substantial difference in fuel consumptions improvement regardless the control methods except high load condition. Also it is observed that there exist critical EGR rates around which the combustion performance and NOx formation change remarkably and these rates generally coincide with optimum rates for the fuel consumption. In addition, dilution with fresh air is much more advantageous than that of the exhaust gas from the view point of dilution limit and fuel consumption, while utilization of the exhaust gas is more effective on NOx reduction in spite of considerably small dilution compared with the use of fresh air. Finally, the improvement of fuel consumption by massive EGR is highly dependent on the EGR limit at which the engine runs stably, therefore the stratified combustion technique might be a best solution for this purpose.

• 대한기계학회논문집B
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• 제24권2호
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• pp.161-168
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• 2000

Lean combustion in a SI engine is one of the best solution for the improvement of fuel economy and reduction of pollutant emission. In order to access a lean combustion engine, stable combustion at lean AlF ratio is needed. In this paper, the effect of fuel injection timing on lean misfire limit has been investigated in an MPI engine. To investigate the interaction of injection timing and intake flow characteristics, three different swirl generating SCV(swirl control valve) configurations were considered, and investigated their effects on lean misfire limit and torque at full load operation. Also the effects of spark timing on lean combustion has been investigated. Lean combustion has been examined and the results are reported in this paper. SCV B has been developed to satisfy the requirements of sufficient swirl generation to improve lean combustion and stable performance. It is found that injection timing, spark timing and intake air motion govern the stable lean combustion.

• 한국자동차공학회논문집
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• 제11권3호
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• pp.92-98
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• 2003

An LPG engine for heavy-duty vehicles has been developed using liquid phase LPG injection (hereafter LPLi) system which has regarded as one of the next generation LPG fuel supply systems. In this wort to investigate the lean bum characteristics of heavy-duty LPLi engine, various injection timing (SOI, start of injection) and double ignition method were tested. The results showed that lean misfire limit of LPLi engine could be extended. by 0.2 $\lambda$ value, using the optimal SOI timing in LPLi system. Double ignition method test was carried out by installing the second spark plug and modified ignition circuit to ignite two spark plugs simultaneously. Double ignition resulted in the stable combustion under ultra lean bum condition, below $\lambda=1.7$, and extension of lean misfire limit compare to ordinary case. Therefore, LPLi engine with optimal SOI and double ignition method could be normally operated at around $\lambda=1.9$ and showed higher engine performance.

• International Journal of Automotive Technology
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• 제7권5호
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• pp.519-526
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• 2006

For investigating the effect of fuel stratification on flame propagation, initial flame development and propagation were visualized under different axially stratified states in a port injection SI engine. Stratification was controlled by the combination of the port swirl ratio and injection timing. Experiments were performed in an optical single cylinder engine modified from a production engine and images were captured through the quartz window mounted in the piston by an intensified CCD camera. Firstly in this paper, the characteristics under no port-generated swirl condition, i.e. normal conventional case was studied. Under various stratified conditions, flame images were captured at the pre-set crank angles. These were averaged and processed to characterize the flames propagation. The flame stability was estimated by the weighted average of flame area and luminosity. The stability was also evaluated through the standard deviation of flame area and propagation distance, and mean absolute deviation of propagating direction. Results show that stratification state according to injection timing do not affect on the direction of flame propagation. The flame development and the initial flame stability are strongly dependent on the stratified conditions and the initial flame stability is closely related to the engine stability and lean misfire limit.

• Journal of Mechanical Science and Technology
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• 제18권10호
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• pp.1809-1818
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• 2004

The dependence of the ignition timing in an HCCI engine on intake temperature and pressure, equivalence ratio, and fuel species is investigated with a zero-dimensional model combined with a detailed chemical kinetics. The accuracy of the model is evaluated by comparing measured and computed results in a propane-fueled HCCI engine. It is shown that the peak pressure values are reproduced within 10% and ignition timing within 5$^{\circ}$ CA. The heat loss through the walls is found to affect significantly on the ignition timing for different inlet conditions. It is also shown that for the propane-fueled engine, the tolerance in intake temperatures is 20-25K and the tolerance in intake pressure is about 1 bar for stable operation without misfire or too early ignition. Comparison of propane and heptane fuels indicates that the tendency to misfire when heptane is employed as the fuel is less than that when propane is employed with the same wall temperature conditions. However, the heptane-fueled engine may have a lower compression ratio to avoid too early ignition and hence lower efficiency. For the selected set of engine parameters, stable operations might be achieved for the heptane-fueled engine with twice as much tolerance in intake temperatures as for the propane-fueled engine.

• 한국자동차공학회논문집
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• 제22권2호
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• pp.156-165
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• 2014

This paper is the first investigation on the effect of flow control methods on the part load performance in a spark ignition engine. For comparison of the methods, two control devices, port throttling and masking, were applied to a conventional engine without any design change of the intake port. Steady flow evaluation shows that steady flow rates per unit opening area and swirl ratio are very low compared with the port throttling and saturated from mid-stage valve lift, however, swirl increases slightly as the lift is higher in case of 1/4 masking control. In the part load performance, the effect of simple port throttling on lean misfire limit expansion is limited and insufficient; on the other hand a masking improves the limit considerably without any port modification for increasing swirl. Also the results show that the intake flow control improves the combustion with following two mechanisms: stratification induced by the combination of the flow pattern and the fuel injection timing attribute to ignition ability and the intensified flow ensure fast burn. In addition fuel consumption reduces under the flow controls and the reduction rate is different according to the operation conditions and control methods. At the Stoichiometric and/or low speed and low load the throttling method is more advantageous; however vice versa at lean and high load condition. Finally, the throttling is more efficient for HC reduction than masking, on the other side the NOx emissions increase under the masking and decrease under the port throttling compared with conventional port scheme.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3282-3287
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• 2007

Lean combustion is one of the most promising method for increasing engine efficiency and reducing the exhaust emission from SI gas engines. Due to the possibility of partial burn and misfire, however, under lean burn operation, stable flame kernel formation and fast burn rate are needed to guarantee a successful subsequent combustion. Experiment data were obtained on a single-cylinder CNG fueled SI engine to investigate the effect of direct injection, spark timing and variation of injection timing. Experimental results show that lean burn limit is ${\lambda}$=1.3 with port injection, and expansion of lean burn limit ${\lambda}$=1.4 with direct injection method, due to increase of turbulence intensity in cylinder and stratified charge. Combustion duration in lean region is improved by using the variation of injection timing.

• 대한기계학회논문집B
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• 제24권9호
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• pp.1157-1165
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• 2000

A classic examples of the abnormal combustions are the knock and misfire, which raise noxious performance and life of the engine. A heavy knock can also cause severe damages to the engine itself, which gives more reason why it must be detected and corrected. With the response of the today's requirements, we have researched the new diagnostic system which uses the breakdown voltage characteristics between electrodes of spark plug. This breakdown voltage depends on the pressure, temperature and even the shape and material of electrodes. But there is no data of breakdown voltage in case of using the spark plug as a electrodes. So, in this study, we show the breakdown voltage characteristic by pressure and temperature in constant volume bomb, which will make it possible to diagnose the engine combustion phenomenon.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제24회 춘계학술대회논문집
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• pp.159-167
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• 2005

Considering the increase of interest in $H_{2}O_2$ as a rocket propellant, a test facility and a rocket engine have been developed to research in areas of $H_{2}O_2$ mono-propellant propulsion. A detailed design-study of a $H_{2}O_2$ mono-propellant rocket engine of 100-N thrust is presented. Several firings attempted in early stage had some problems with misfire and chamber pressure decrease. Low environmental temperature and impurities included in hydrogen peroxide were considered to be the reasons. Addressing these points resulted in successful firing of the rocket engine and obtained thrust about $100\sim107-N.$