Search Results

A dedicated closed-loop propane fuel system has been developed for the General Motors Medium Duty truck with a 7.4 liter engine. The fuel metering system consists of a closed-loop controlled regulator and mixer. Regulator output pressure is controlled by a pulse-width modulated vacuum signal from the mixer for off-idle operation. Idle fuel is provided by an electronically controlled, fuel metering solenoid valve. Additionally, original equipment manufacturer (OEM) fail-safe performance of the Electronic Throttle Control system has also been achieved. This fuel system is an example of how an open loop regulator-mixer system can be enhanced with electronic controls to achieve significant improvements in emission signature, driveability, and customer satisfaction.

Liquefied Petroleum Gas (LPG) and Compressed Natural Gas (CNG) have long been recognized as ideal clean and potentially available fuels for motor vehicles. However, some disadvantages of the two gaseous fuels such as lower energy density (kW/l) compared to gasoline, a loss of power in unmodified converted engines relative to gasoline and the current shortage of refueling stations hamper their widespread use. Additionally, engines with throttle-body gaseous fuel fumigation need longer cranking time and exhibit relatively slow response during transient engine operation. To alleviate the above shortcomings, a low cost dual-fuel system was developed. The prototype system uses a mixture of gaseous fuel (Liquefied Petroleum Gas) and gasoline to enhance fuel economy, drivability, and lower emissions. The two fuels can be mixed at any percentage depending on the customer's need.

A group of GM C-2500 heavy-duty and GM C-1500 light-duty trucks were modified to bi-fuel compressed natural gas (CNG)/gasoline and liquefied petroleum gas (LPG)/gasoline vehicles. The fuel management systems used for different model year vehicles were introduced. The Alternative Fuel Technology (AFT) System used for 1997 GM C-2500 trucks is discussed in detail. AFT is an automatic switching bi-fuel system which is able to control fuel flow rate, spark timing, and EGR, and perform On-Board Diagnostics (OBD-II). The exhaust emissions of carbon monoxide (CO), total hydrocarbon (HC) and oxides of nitrogen (NOx) were measured using dilute sampling techniques. The vehicles tested were operated on a chassis dynamometer and run on the Federal Test Procedure (FTP) Urban Schedule.