Westport Innovations Inc. • High Pressure Direct Injection

Application: heavy-duty trucks
High-Horsepower Applications: mine-haul trucks, power generators

BENEFITS relative to comparable diesel engines:

Nitrogen Oxides (NOx) emissions reduced by 40-50%
Particulate Matter (PM) emissions reduced by approximately 80%
Greenhouse Gas (GHG) emissions reduced by 20% to 25%
Same or better thermal efficiency
Same engine power and torque
Reduced dependence on oil for trucking and other high fuel use transportation applications

Technology Description
High Pressure Direct Injection relies on late-cycle high-pressure injection of a gaseous fuel, such as natural gas, into a combustion chamber of an internal combustion engine. The natural gas is injected at the end of the compression stroke, just like the diesel fuel is injected at the end of the compression stroke in a diesel engine. Under the pressures found in the combustion chamber of a normal diesel engine, natural gas requires higher ignition temperature than diesel (circa 800° C vs. 500° C) to maintain acceptable ignition delay period of less than 1 millisecond. To assist with the ignition of natural gas, a small amount of diesel fuel is injected into the engine cylinder using the same injector followed by the main natural gas fuel injection. This diesel fuel acts as a pilot or “liquid spark plug” which ignites rapidly the hot combustion products then igniting the natural gas.

HPDI allows diesel-cycle operation with over 90% replacement of diesel fuel. Compared to other natural gas engines, because of Westport's direct injection approach, HPDI also eliminates both part-load throttling and limits on torque due to the onset of knock. Diesel pilot-ignition has two distinct advantages: durability and ignition quality. Diesel injection systems are inherently durable as demonstrated by conventional experience. In addition, multiple ignition sites can be easily arranged (close to one per gas jet).

We recently unveiled Westport’s lower emission, homogenous charge direct injection (HCDI) approach for low NOx, high efficiency applications. HPDI and HCDI technologies combine the clean and flexible combustion attributes of natural gas with easily ignitable diesel fuel. At the same time, it replaces over 90% of diesel fuel with natural gas and produces NOx levels as low as 0.2g/bhp-hr.

How it works

A dual-concentric needle injector enables small quantities of diesel fuel and large quantities of natural gas to be delivered at high pressure to the combustion chamber. The diesel fuel is delivered just prior to top-dead-centre, followed by the main fuel quantity of natural gas. Depending upon final calibration and duty cycle, natural gas displaces around 90-95% of the diesel fuel (on an energy equivalent basis).