Experimental and statistical investigation of different valve lifts on HCCI combustion, performance and exhaust emissions using response surface method

Abstract

To determine the optimum running parameter in HCCI engine is critical for stable and efficient operation, because misfiring, knocking and narrower operating range problems can be seen in HCCI combustion. So in the current study, the influences of valve mechanisms, engine speed, lambda, and inlet air temperature on the performance and exhaust emission of the HCCI engine and its optimization was conducted by response surface method (RSM). The responses were selected as effective torque (ET), brake specific fuel consumption (BSFC), indicated thermal efficiency (ITE), and emissions (UHC, CO, and NOx). The desirability function was used to define an optimum combination of engine operating conditions. The highest desirability function was found as 72% and achieved at 1168.82 rpm engine speed and lambda ratio of 0.971, inlet air temperature of 100.07 °C, and valve lift In 5.5-Ex 3.5 mm. These input variables were recommended as optimum HCCI engine operating conditions. Responses such as ET, BSFC, and ITE, were achieved at this point as 16.4 Nm, 236.936 g/kWh, and 21.55%, respectively. In addition, the optimum exhaust emission values were found to be 442.19 ppm for UHC, 2.42% for CO, and 468.964 ppm for NOx.