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Shim, Euijoon,Park, Hyunwook,Bae, Choongsik Elsevier 2018 APPLIED ENERGY Vol.225 No.-
<P><B>Abstract</B></P> <P>Single fueled advanced combustion technologies, such as homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI), and low temperature diesel combustion (LTC), could make it possible to escape nitrogen oxides (NOx) and particulate matter (PM) generation. However, single fueled advanced combustion technologies have several challenges to overcome in order to be commercialized, such as combustion phase control, low combustion stability, narrow operating ranges, high level of maximum pressure rise rate (MPRR), and high amounts of unburned hydrocarbon (HC) and carbon monoxide (CO) emissions. Dual-fuel premixed charge compression ignition (DF-PCCI) combustion concepts have suggested many solutions to overcome the drawbacks of single-fueled advanced combustion technologies, such as combustion phase control, combustion stability, and limited operating range. However, high amounts of unburned HC and CO emissions are still regarded as the main hurdles of DF-PCCI combustion. In this study, the effects of global equivalence ratio ( <SUB> ϕ global </SUB> ) and initial charge temperature, which were controlled by means of intake throttling, charge heating, and exhaust gas recirculation (EGR) strategies, were investigated to overcome the bulk quenching phenomenon under low load conditions of DF-PCCI operation in a heavy-duty (HD) single cylinder engine. The optimized intake charge strategy which used the throttle and hot-EGR, showed the possibility of simultaneous HC and CO reduction, combustion efficiency ( <SUB> η c </SUB> ) improvement, and combustion stability enhancement while satisfying NOx and PM emissions under EU-VI regulations. The results suggest that controlling the charge air quantity and charge temperature is an effective way to mitigate the bulk quenching phenomenon under low load conditions on DF-PCCI.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bulk quenching phenomenon produces high amounts of HC and CO emissions in dual-fuel premixed charge compression ignition. </LI> <LI> Controlling the global equivalence ratio amitigates the bulk quenching phenomenon. </LI> <LI> Controlling the initial charge temperature mitigates the bulk quenching phenomenon. </LI> <LI> Optimized charge control strategy in dual-fuel premixed charge compression ignition to reduce CO<SUB>2</SUB> emission. </LI> </UL> </P>
부분 예혼합압축착화 엔진 저부하 운전영역에서의 디젤 분사전략
박현욱(Hyunwook Park),심의준(Euijoon Shim),황영훈(Younghoon Hwang),배충식(Choongsik Bae) 한국자동차공학회 2018 한국 자동차공학회논문집 Vol.26 No.3
A diesel injection strategy in a premixed charge compression ignition(PCCI) engine was investigated under low load conditions. The main injection timing of the PCCI combustion was selected based on the simultaneous reduction of nitrogen oxides(NOX) and unburned hydrocarbon(UHC) emissions at an exhaust gas recirculation(EGR) rate of 30 %. Despite the main injection timing chosen, too advanced combustion phasing resulted in increased fuel consumption. Therefore, combustion phasing was effectively retarded by an additional EGR. Double injection strategy was implemented to reduce in-cylinder wall wetting. The UHC and carbon monoxide(CO) emissions were significantly reduced by optimizing pilot injection timing and quantity. In conclusion, the UHC and CO emissions were reduced effectively in the PCCI combustion using the double injection strategy and appropriate EGR rate, which resulted in increased combustion efficiency and improved fuel economy.
Park, Hyunwook,Shim, Euijoon,Bae, Choongsik Elsevier 2019 Fuel Vol.235 No.-
<P><B>Abstract</B></P> <P>Dual-fuel premixed charge compression ignition (DF-PCCI) combustion has been demonstrated as a promising solution for simultaneous reduction of nitrogen oxides (NO<SUB>X</SUB>) and particulate matter (PM) emissions in heavy-duty compression ignition engines. The use of natural gas (NG) as the low-reactivity fuel in DF-PCCI combustion can expand the limited range of high load operations owing to the lower reactivity of NG than that of gasoline. However, the lower reactivity of NG results in significant hydrocarbon (HC) and carbon monoxide (CO) emissions at the low load operations. In this study, the mixture formations with and without exhaust gas recirculation (EGR) in NG-diesel DF-PCCI combustion were assessed to reduce the HC and CO emissions as well as to improve the fuel economy at low load operations. Diesel injection timing and NG substitution ratio (SR), which is defined as the proportion of energy stored in NG with respect to the total energy amount, were changed to examine the effects of the mixture formation on the DF-PCCI combustion. The NG SR, which was required to maintain the combustion phasing at a constant crank angle degree (CAD), was increased as the diesel injection timing was retarded in the mixture formation without EGR. The introduction of EGR, in addition to the diesel injection timing and the NG SR, contributed to the favorable mixture formation for the low load operations. The NO<SUB>X</SUB> and PM emissions were lower than the EURO VI limitations in both the mixture formations with and without EGR. When the EGR rate of 50% was applied, the indicated thermal efficiency (ITE) increased compared to the case without EGR. The increased ITE was due to the improved combustion efficiency, the higher peak heat release rate (HRR), and the shorter combustion duration. The HC and CO emissions also decreased significantly with the EGR.</P>
Park, Hyunwook,Shim, Euijoon,Bae, Choongsik Elsevier 2019 Energy conversion and management Vol.194 No.-
<P><B>Abstract</B></P> <P>Dual-fuel premixed charge compression ignition (DF-PCCI) combustion can achieve low nitrogen oxides (NO<SUB>X</SUB>) and particulate matter (PM) emissions for wide ranges of engine operations. However, the deterioration in thermal efficiency, and hydrocarbon (HC) and carbon monoxide (CO) emissions at low loads were recognized as the barriers for expanding the low-load operating range. In this study, the causes of the barriers were investigated and a mixture preparation strategy was suggested for overcoming the barriers in a natural gas (NG)-diesel DF-PCCI engine. Combustion and energy balance analysis was conducted to evaluate the strategy. Baseline DF-PCCI was determined by combinations of diesel start of injection (SOI) and NG substitution ratio (SR) at low loads from 0.3 to 0.6 MPa indicated mean effective pressure (IMEP). An increase in the homogeneity of a fuel-air mixture in the baseline DF-PCCI effectively reduced the NO<SUB>X</SUB> and PM emissions but increased the HC and CO emissions in each low-load operation. As the engine load was decreased, the formation of an overly-lean mixture intensified the effects of the mixture homogeneity. Therefore, the thermal efficiency, and HC and CO emissions deteriorated at 0.3 MPa IMEP. A mixture stratification strategy was established to increase the local equivalence ratio and reactivity of the fuel-air mixture. The strategy was realized by a retarded diesel SOI, a lower NG SR, and a higher exhaust gas recirculation rate. The strategy increased the degree of constant volume combustion by enhancing the combustion performance. The enhanced combustion reduced the combustion loss, and thus, improved the thermal efficiency. The HC and CO emissions also decreased mainly due to the improved combustion and the reduced mass flow rates of the NG.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Dual-fuel PCCI reduced NO<SUB>X</SUB> and PM emissions by increasing mixture homogeneity. </LI> <LI> The increase of the mixture homogeneity increased HC and CO emissions at low loads. </LI> <LI> Mixture stratification improved the thermal efficiency in dual-fuel PCCI at low loads. </LI> <LI> Mixture stratification effectively reduced the HC and CO emissions at low loads. </LI> </UL> </P>