Some very interesting advances in gaseous fueling are taking place at Westport Innovations and its joint venture partnership, Cummins-Westport in Vancouver, British Columbia, Canada.

As you may already know, today's CNG engines require a spark plug to control combustion and are limited to compression ratios of around 11 to 1. (Passenger car engines operate at compression ratios around 9 to 1.)

Diesels are compression ignited meaning they utilize the heat generated by the extreme compression of air in the cylinder to provide the heat needed for combustion. Because the compression ratio in a diesel is typically at 18 to 1 or higher, diesels are inherently more efficient. (They have a greater thermal efficiency than low compression, spark ignited engines). The challenge has been to find a way to combine the use of compression ignition technology with a very clean, high hydrogen, clean-burning fuel such as natural gas.

Cummins-Westport may have solved this problem! The first development is the progress being made with the Cummins-Westport high-pressure injection system for diesel (compression ignition) engines.

The heart of this system is a dual purpose fuel injector capable of injecting both natural gas and diesel fuel into the combustion chamber. A small amount of diesel fuel (no more than 20 percent of the fuel quantity per stroke) is injected as a pilot fuel to initiate combustion. CNG is injected to provide most of the energy (approximately 80 percent) for the power stroke. The engine operates as a compression ignition engine and has a compression ratio of 18 to 1, yet its primary fuel is natural gas!

The Cummins-Westport High Pressure Fuel Injector is capable of delivering both diesel and natural gas to the combustion chamber of the Cummins diesel engine. NAFTC file photo

One of the major engineering challenges of this concept has been how to obtain the line pressure needed to force a sufficient quantity of natural gas into the combustion chamber as the piston approaches Top Dead Center of the compression stroke. A line pressure of 5000 PSI is required, yet most gaseous fuel systems operate at much lower pressures, typically in the range of 3600 PSI. The problem facing the engineers: How could CNG be pressurized to 5000 PSI onboard the vehicle without the use of a heavy, energy-hungry natural gas compressor?

The answer developed in Vancouver is to use a compressor, but to use a compressor that can operate much more efficiently than a gaseous compressor. Liquids can be pumped more efficiently than gas, since liquids do not compress. Cummins-Westport developed a system that uses LNG (liquefied natural gas) as fuel. A hydraulically driven piston pump, mounted inside the cryogenically chilled LNG storage tank, compresses the LNG to the needed working pressure, about 5000 PSI. The pressurized LNG then leaves the tank and is warmed in a vaporizer. Since LNG is a cryogenic fuel (-250 degrees F), it will vaporize (turn to a gas) when it is warmed no matter how much pressure it is under. The highly pressurized natural gas is now available for use as fuel for the engine, at a high enough pressure to force it into the high compression diesel combustion chamber. Another positive element of this design is that the engine can run (at greatly reduced power) on diesel fuel alone should the LNG/CNG system malfunction or just run out of fuel!

Detail of the LNG dewar incorporating a hydraulically operated fluid pump within the dewar that pressurized the LNG to a pressure of 5000 PSI before it exits the container. Note the frost that has accumulated on the pump head. NAFTC file photo

The result of this design is a clean-burning, compression ignition engine with diesel efficiency! A semi-truck is currently running evaluation trials using this fuel system mated to a Cummins ISG series engine and fueled by two saddle mounted LNG dewars.

Cummins-Westport is using twin dewars, each containing the high pressure pump, on its evaluation vehicle. NAFTC file photo

The other exciting news at Westport Innovations is the development of a 100 percent gaseous-fueled (CNG) engine which is running at diesel compression ratios (18 to 1)! While this was considered an impossibility just a few years ago, Westport has developed the technology to make it happen. The secret, in addition to computer-controlled CNG injection technology, is a simple glow plug as an ignition source. The CNG is injected at conventional pressures, around 3000 PSI ,and the combustion process is initiated by the heat supplied by a ceramic type glow plug.

Ceramic glow plugs are being widely used in current production diesels. They achieve full heat within seconds and are more durable and energy efficient. Photo courtesy of The Robert Bosch Corporation.

The engine being used for test cell trials is an Isuzu 6 cylinder medium duty diesel. Should this system prove viable, I believe it will revolutionize the medium duty (bus and truck) industry with its ability to deliver the thermal efficiency of a diesel and the low emissions of natural gas without the complex spark ignition systems required by today's CNG engines.

Westport is also continuing their research into the uses of HCNG. HCNG is a blend of hydrogen and natural gas. Most HCNG blends consist of 20% hydrogen and 80% natural gas. Although HCNG fuel has a lower energy density than natural gas (meaning it has a reduced operating range), the additional hydrogen in the combustion chamber greatly reduces the production of NOx. In fact, a NOx reduction of up to 50 percent has been reported in some cases. Thus HCNG could provide very low NOx levels in urban environments where NOx is a critical pollutant. The other justification for the development of HCNG fuel systems is to help develop a transportation based demand for hydrogen. It is hoped that promoting the use of HCNG as a fuel for transportation will drive the development of the hydrogen fueling infrastructure which will be required if we are to transition to a hydrogen-fueled transportation system.

HCNG must be blended in a special mixing vessel, pictured here. Note the hydrogen and CNG metering controls behind the spherical mixing vessel. NAFTC file photo