Clean Air Power
, the Oxford-based company developing a system allowing engines to operate on a combination of diesel and natural gas, has been granted two patents that it claimed will boost the prospects for its technology worldwide.
In the US, it has been granted a patent covering the application of homogenous charge compression ignition (HCCI) to its Dual Fuel system, which makes engines work in a similar way to diesel units but generates power by burning mostly clean, natural gas. HCCI is a hybrid of traditional spark ignition and the compression ignition process found in diesel, and will be used to reduce emissions from internal combustion.
With the Dual Fuel system, a measured quantity of natural gas is mixed with air before it enters the cylinder. This fuel-air mixture is then compressed to the same levels of the diesel engine, thus maintaining efficiency.
However, due to its resistance to compression ignition, the natural gas mixture does not ignite spontaneously. Rather, the Dual Fuel engine uses a small injection of diesel fuel, around 10 per cent of the total fuel, to ignite the gas and air charge.
The 'pilot' injection behaves like a group of spark plugs, setting off clean and efficient combustion of the lean gas-air mixture. As a result, the technology allows a diesel engine to perform to a similar efficiency and power on natural gas, while cutting fuel costs and producing lower levels of CO2 and other harmful emissions.
Micropilot takes the process one step further, with an even greater reduction of emissions from Dual Fuel engines by lowering the quantities of diesel pilot injections. A technical paper published by the company claimed that smaller diesel injections of one to two per cent of the total fuel can reduce NO2 emissions by 80 per cent, while also reducing CO2 output.