High-pressure direct injection of natural gas in a diesel engine for high performance/low emissions
The North American mining industry faces challenging emissions regulations in future years with the introduction of new standards for off-road diesel engines. In order to remain competitive, industry stakeholders must invest in new technologies that are economically and environmentally sustainable.
Westport Innovations Inc., in Vancouver, British Columbia, has developed high-pressure direct injection (HPDI) technology that allows diesel engines to run primarily on natural gas with no intrusive engine modifications while reducing emissions of NOx, particulate matter, and CO2 with no loss in performance. This is accomplished through late-cycle, high-pressure direct injection of natural gas into a diesel engine combustion chamber at the end of the compression stroke. A small amount of diesel fuel is injected first to initiate combustion, followed by the main natural gas fuel injection. The diesel cycle and its operating characteristics are fully retained including high combustion efficiency, low-speed torque, high-power output, no engine knock, and fast response to load changes. Traditionally, natural gas has not been an attractive fuel alternative in mining operations due to reduced performance associated with spark ignition engines and the added weight and space required for compressed natural gas tanks. However, liquefied natural gas (LNG) can be stored with less impact on weight and space than compressed natural gas (CNG) by virtue of its increased energy density.
Westport has applied HPDI technology to the Cummins QSK series engines for high horsepower applications such as power generation and mine haul trucks. HPDI can also be applied to other engine manufacturer platforms and market applications. Westport is interested in demonstrating the unique characteristics of HPDI in mine haul trucks to show diesel performance with low emissions levels using low-cost LNG fuel.
Retrofitting a Tier I engine with HPDI would provide emission reductions below the EPA 2006 Tier II standards while maintaining the performance and efficiency of the Tier I platform. The longer term target is the “Blue-Sky” voluntary standards of 3.8 g/kW-hr (2.8 g/bhp-hr) of NOx + nmHC and 0.12 g/kW-hr (0.09 g/bhp-hr) of PM and Tier III standards. Typically, an HPDI engine is capable of reducing NOx emissions by 40% over diesel operation at the same efficiency. On a mining truck meeting Tier II standards, this NOx reduction would amount to approximately 14 t/yr less than in diesel operation. PM emissions are typically reduced by some 60% with HPDI fueling, which would translate into a yearly reduction of 650 kg. Similarly, engine-out greenhouse gas (GHG) emissions are reduced by 21%, resulting in a yearly reduction of approximately 950 t per vehicle.
As well as emission reductions, efficient natural gas usage in mine haul operations would offer significant benefits in terms of fuel cost savings, which may be further combined with monetary emission credits. HPDI technology would enable operators to exercise environmental stewardship while gaining a competitive advantage in advance of new Tier II and Tier III emissions regulations. The advantages of natural gas use among mine haul truck operations can be replicated across a broad range of engines and applications.