A significant performance issue for LNG vehicles is the drop in power and fuel economy due to the use of spark-ignition engines. The use of diesel-LNG dual fuel allows a heavy duty vehicle to retain the high fuel efficiency and low maintenance of a compression ignition engine while benefiting from the substitution of higher-priced diesel fuel with much lower-priced LNG. The EcoDiesel System the most advanced diesel dual fuel system on the market today and is fully customizable for maximum performance and fuel economy of any diesel engine. Continuing with compression-ignition eliminates the need to maintain the ignition system of a new or repower spark-ignition LNG engine. Supplying a homogeneous natural gas fuel mixture post-turbo also minimizes natural gas injection maintenance costs, especially as compared to the cost of maintaining a direct LNG injection system into the combustion chamber.
Many of problems encountered by the previous cases appear to have originated with the LNG fuel storage system. The automotive LNG fuel systems must be designed specifically for mobile applications and not just repackaging industrial gas systems to fit onto vehicles. Things to look for an automotive system are:
- No economizer. Only liquid fuel must be supplied to the vaporizer.
- Adequate insulation. Ambient heat gain must be kept to the minimum possible.
- No in-tank heaters. Tanks must be pressurized after filling with backpressure to keep LNG as cold as possible, which avoids the need for saturation pressure.
- Uniform LNG fuel temperature. There must be no temperature stratification within the LNG tank and this requires an automotive vapor return filling system.
Keeping the fuel temperature as cold as possible at all times is the key to having an properly functioning automotive LNG fuel system. Cold fuel keeps fuel costs low, ensures consistent fuel mixtures for the engine, and maximizes the range from an LNG tank.
Only Cryogenic Fuels Inc appears to provide an LNG system that incorporates the above considerations at this time.