A dual fuel engine is an engine designed to burn predominantly natural gas but with a small percentage of diesel as a pilot fuel to start ignition. The engines operate on a cross between the diesel and the Otto cycles. In operation, a natural gas-air mixture is admitted to the cylinder during the intake stroke, then compressed during the compression stroke. At the top of the compression stroke the pilot diesel fuel is admitted and ignites spontaneously, igniting the gas-air mixture to create the power expansion. Care has to be taken to avoid spontaneous ignition of the natural gas-air mixture, but with careful design the engine can operate at close to the conditions of a diesel engine, with a high-power output and high efficiency, yet with the emissions close to those of a gas-fired spark-ignition engine.
Typical dual fuel engines operate with between 1% and 15% diesel fuel. Since a dual fuel engine must be equipped with diesel injectors, exactly as if it were a diesel engine, a dual fuel engine can also burn 100% diesel if necessary, although with the penalty of much higher emissions.
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Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.