I googled dual fuel diesel engines
and got this.Current Dual-FuelTM TechnologyThe Dual-FuelTM engine uses the same diesel engine, but generates power by burning mostly clean natural gas. The diesel engine operates unchanged, but from the outset, a measured quantity of natural gas is mixed with the air just before it enters the cylinder. This lean fuel-air mixture is then compressed to the same levels of the diesel engine, thus maintaining efficiency. Due to its resistance to compression ignition, the natural gas mixture does not ignite spontaneously under the compression. Instead, the Dual-FuelTM engine uses a small injection of diesel fuel, around 10% of the total energy of the fuel, to ignite the main charge of gas and air. This small “pilot” injection acts like a multitude of microscopic spark-plugs, setting off clean and efficient combustion of the lean gas-air mixture.The natural gas burns cleaner than diesel, resulting in much lower harmful emissions. With fuel-efficiency similar to that of the original diesel engine, CO2 emissions are reduced by up to 25% due the inherently low carbon content of natural gas. Although approximately 90% of the diesel is replaced by natural gas, a similar level of power is generated by the energy released from the gas combustion and the efficiency therefore remains similar to the original diesel engine. Clean Air Power is unaware of any dedicated natural gas trucks that can match a Dual-FuelTM truck for efficiency and performance. Thus, Dual-FuelTM technology enables the diesel engine to operate with comparable efficiency and power on natural gas, benefiting from lower harmful emissions, lower CO2 and lower fuel costs.http://www.cleanairpower.com/?p=dual_fuel