Yazar "Yucesu, H. Serdar" seçeneğine göre listele

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    An experimental investigation on combustion and performance characteristics of supercharged HCCI operation in low compression ratio engine setting
    (Pergamon-Elsevier Science Ltd, 2020) Polat, Seyfi; Yucesu, H. Serdar; Uyumaz, Ahmet; Kannan, Kaushik; Shahbakhti, Mahdi
    This study investigates the effects of boost pressure on combustion and performance of an early direct injection homogenous charge compression ignition (HCCI) engine at a low compression ratio (CR). A 2.0 L, four-cylinder, four-stroke, gasoline direct injection engine was converted to operate in early direct injection HCCI mode. In addition, a supercharger unit was developed for engine boosting. The experiments were performed at different intake manifold absolute pressures (MAP) from 1.0 to 1.6 bar at different engine loads using n-heptane fuel. The effects of boost pressure were investigated on HCCI combustion and engine performance characteristics using volumetric efficiency, in-cylinder pressure, heat release rate (HRR), maximum in-cylinder pressure and gas temperature, CA50 (crank angle by which 50% of the fuel is burnt), combustion duration, apparent combustion efficiency, indicated mean effective pressure (IMEP), brake mean effective pressure (BMEP), friction mean effective pressure (FMEP), indicated thermal efficiency (ITE), brake thermal efficiency (BTE), heat loss, exergy of heat loss, coefficient of variation of IMEP (COVIMEP), maximum pressure rise rate (MPRR) and ringing intensity (RI). The experimental results showed that high-efficiency HCCI operation is feasible at an engine compression ratio as low as 9.2 once the engine variables are properly optimized and an appropriate level of supercharging is utilized. An increase in indicated thermal efficiency was seen as boost pressure increased. In addition, combustion phasing advanced by increasing boost pressure or increasing air-fuel equivalence ratio values. Combustion events with CA50 2-3 degrees CA aTDC show the highest thermal efficiency especially at low boost pressure conditions. In addition, the pressure rise rate and ringing intensity increased by increasing air-fuel equivalence ratio and MAP. The test results also showed that HCCI operating range can be extended with the increase of intake manifold pressure especially at high load limits.
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    Öğe
    An Experimental Research on the Effects of Negative Valve Overlap on Performance and Operating Range in a Homogeneous Charge Compression Ignition Engine With RON40 and RON60 Fuels
    (Asme, 2020) Polat, Seyfi; Solmaz, Hamit; Uyumaz, Ahmet; Calam, Alper; Yilmaz, Emre; Yucesu, H. Serdar
    In this study, the effects of negative valve overlap (NVO) on homogenous charge compression ignition (HCCI) combustion and engine performance were experimentally investigated. A four stroke, single cylinder, port injection HCCI engine was operated at -16 deg crank angle (CA), -8 deg CA, and +8 deg CA valve overlap values and different lambda values and engine speeds at wide open throttle. RON40 and RON60 were used as test fuels in view of combustion and performance characteristics in HCCI mode. The variations of indicated mean effective pressure (IMEP), residual gas, CA50, indicated thermal efficiency (ITE), indicated specific fuel consumption (ISFC), maximum pressure rise rate (MPRR) and ringing intensity (RI) were observed on HCCI combustion. The results showed that NVO caused to trap residual gases in the combustion chamber. Hot residual gases showed heating and dilution effect on HCCI combustion. Combustion was retarded with the presence of residual gas at -16 deg CA NVO. Test results showed that higher imep and maximum in-cylinder pressure were obtained with RON60 according to RON40. As expected, CA50 was obtained later with RON60 compared to RON40 due to more resistance of auto-ignition. RON60 residual gas prevented the rapid and sudden combustion due to higher heat capacity of charge mixture. RI decreased with the usage of RON60 compared to RON40. Significant decrease was seen on RI with RON60 especially at lower lambda values. It was seen that HCCI combustion can be controlled with NVO and operating range of HCCI engines can be extended.