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In a dual fuel engine a primary fuel that is generally gaseous is mixed with air, compressed and ignited by a small pilot spray of diesel as in a diesel engine. Dual fuel engines suffer from the problems of poor brake thermal efficiency and high HC emissions, particularly at low outputs. In the present experimental work, the effects of intake charge temperature, pilot fuel quantity, exhaust gas recirculation and throttling of the intake on improving the performance of a LPG-diesel dual fuel engine have been studied. Results indicate that at low outputs an increase in the intake temperature and pilot quantity is advantageous. HC level generally reduces with increase in pilot quantity and intake temperature. Exhaust gas recirculation (EGR) coupled with intake heating raises the brake thermal efficiency and lowers HC emissions. With throttling and EGR there is a significant reduction in the HC levels and an improvement in brake thermal efficiency at low loads.

Pilot fuel quantity and intake temperature are two important parameters controlling the combustion process in dual fuel engines. Experiments were conducted on a LPG diesel dual fuel engine at various intake temperatures and pilot quantities. Ignition delay, rate of pressure rise, combustion duration and heat release patterns have been presented at low and high loads. An increase in the concentration of the gaseous primary fuel significantly increased the ignition delay. At high outputs the combustion of the gas by flame propagation which follows the ignition process of the pilot and the entrained gas was the dominant feature. However, at low loads combustion of the pilot fuel and the gas entrained in it were only significant.. The rapid combustion of the gaseous fuel at high output conditions, particularly when the intake temperature was high, resulted in rough engine operation.