Search for renewable fuels such as vegetable oils, in particular non-edible vegetable oils, has become more pertinent in the context of the fossil fuel crisis and vehicle population explosion. The drawbacks associated with vegetable oils for use in diesel engines call for a hot combustion chamber. The concept of the low heat rejection diesel engine is gaining prominence for adopting vegetable oils as substitute fuels for conventional diesel fuel. Non-edible vegetable oils such as Pongamia oil and Jatropha curcas oil are found to be efective substitute fuels in the low heat rejection diesel engine. EsteriRcation, preheating and increase in injection pressures have been tried for efective utilization of the vegetable oils. Performance parameters such as the brake specific energy consumption (b.s.e.c.) and exhaust gas temperature (EGT) have been reported for varying magnitudes of brake mean efective pressure (b.m.e.p.) with diferent non-edible vegetable oils as substitute fuels. The pollution levels of black smoke and NOx have been recorded. Combustion diagnosis is also carried out with the aid of a miniature piezoelectric pressure transducer and TDC (top dead centre) encoder.