Westport™ HPDI (high-pressure direct injection) technology uses natural gas as the primary fuel, along with a small amount of diesel as an ignition source or “liquid spark plug”.
At the heart of the engine is a revolutionary patented injector with a dual-concentric needle. It allows for small quantities of diesel fuel and large quantities of natural gas to be delivered at high pressure to the combustion chamber.
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 a higher ignition temperature than diesel (about 800°C vs. 500°C) to maintain an 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 followed by the main natural gas fuel injection. The diesel acts as a pilot or “liquid spark plug” which rapidly ignites the hot combustion products, thus igniting the natural gas.
HPDI allows diesel-cycle operation with approximately 95% replacement of diesel fuel (by energy). This technology uses a cheaper, cleaner-burning fuel than diesel with no compromises on engine torque, power, fuel economy, or driveability while at the same time reducing NOx by 50% and CO2 by up to 20%.
