In this study, in order to decrease cold start HC emission at idle and the wide open throttle (WOT) conditions, a thermal barrier layer JBQ was deposited on the top surface of a piston. The engine was tested at three compression ratios of 8 center dot 2, 7.2 and 6 center dot 2 and for two different conditions for each compression ratio. At the first stage, cold start HC emission was measured for the first 180 s. Second, the performance and exhaust characteristics were measured at WOT. Cold start HC emission in the engine with TBL decreased compared to the standard engine at the compression ratios tested. While observing an increase in brake power up to 3 and 5% at the compression ratio of 7 center dot 2 and 6 center dot 2 respectively, the brake power decreased up to 6% at the compression ratio of 8-2 compared to that of the standard engine. Maximum decreases in HC emissions of the engine with TBL piston at WOT were found to be 43 center dot 18, 47 center dot 05 and 32 center dot 12% at the compression ratios of 8 center dot 2, 7 center dot 2 and 6 center dot 2 respectively.