Control System for Diesel - Compressed Natural Gas Engines

Research involving the use of natural gas in internal combustion engines has been intensified due to concerns with the environment and exhaustion of fossil fuels reserves. In Brazil the abundance of natural gas, together with the need to reduce green house gases emissions and noise of urban busses, presented the opportunity to develop a Diesel-CNG control for Diesel engines using a mechanical diesel pump. An add-on system was developed using a production Engine Control Module. In this system, compressed natural gas (CNG) is added into the intake air stream and a pilot injection of diesel is used to achieve ignition. One advantage of the Diesel-CNG system over a diesel engine converted to CNG usage using spark ignition is that the engine can operate in a diesel only mode; not reducing the resale price of the vehicle to regions less served with CNG fueling stations. Pilot diesel injection provides a reliable mode of ignition for lean mixtures of CNG, compared to conventional spark ignition. This paper will describe the Diesel-CNG system in detail and present some performance data.