The objective of this work is to optimize direct injection, single cylinder diesel engine with respect to brake power, fuel economy and smoke emissions through experimental investigation and response surface methodology. A single cylinder 3.8 kW engine was selected for this experimentation. Three parameters viz. compression ratio (CR), injection pressure (IP) and injection timing (IT) were varied and the responses like brake thermal efficiency (BTE), Brake Specific Fuel Consumption (BSFC), Exhaust Gas Temperature (EGT) and smoke opacity (OP) were investigated. Statistical tool like response surface methodology was used to design experiments. Optimization of compression ratio and injection system parameters was performed using the desirability approach of the RSM for superior performance and lesser smoke emissions. A CR of 17.99, IP of 250 bar, and IT of 27 degrees BTDC were found to be optimal values for the Waste Fried Oil Methyl Esters (WFOME) blended with diesel fuel operation in the test engine of 5 HP at 1500 rpm. The results of this study revealed that at optimal input parameters, the values of the BTE, BSFC, EGT and smoke opacity were found to be 29.76%, 0.289 kg/kW h, 298.52 degrees C and 56.49 HSU respectively. (C) 2013 Elsevier Ltd. All rights reserved.