Exam Question

(a) The autoignition temperature of natural gas, approximately 580°C, is significantly higher than that of diesel fuel, which falls between 200 and 300°C. In a dual-fuel engine, during the compression stroke, the temperature at the end of compression may not be sufficiently high to spontaneously ignite natural gas. To overcome this challenge, a method known as pilot injection is employed. A small quantity of diesel fuel is injected, and it serves as an ignition source for the natural gas. The combustion of diesel fuel initiates the ignition process for the entire mixture, allowing for a controlled and efficient combustion of natural gas in the dual-fuel engine.
(b) (i) Otto Cycle:
The engine operates in gas mode during the suction stroke, where a lean air-gas mixture is drawn into the cylinders.
The cylinder head is equipped with a gas admission valve positioned in the air inlet passage, and there is a fuel injector capable of both main and pilot injection.