:In the present work, investigations were carried out on a single cylinder, low compression ratio, spark-assisted low heat rejection D.I diesel engine. An extended electrode spark plug was used. Performance and emission tests on the engine were carried out with diesel fuel at two compression ratios, 10.5 and 12.5. In each case the engine was tested as a normal engine as well as a low heat rejection engine. The test results show that the low compression ratio spark assisted diesel engine operates very smoothly due to the low peak pressure and low rate of pressure rise. The low heat rejection spark assisted diesel engine gave an improved performance and reduced emissions compared to the normal baseline diesel engine. The low heat rejection, spark assisted diesel engine at 12.5 compression ratio gave the best performance among the tested configurations, with an improved thermal efficiency of 3% and a reduced exhaust smoke level of 1.5 Bosch units when compared with normal baseline diesel engine with 16.5 compression ratio.