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Greenhouse Gas Emission Reductions

Greenhouse Gas Benefits of Natural Gas Vehicles

Westport’s Products and Tank to Wheel Emissions

As an engine and fuel system manufacturer, Westport’s first priority is to ensure that our products comply with the latest and most stringent environmental regulations. This has historically been focused on reducing urban air pollutants, an area where natural gas engines and vehicles have been very successful. Increasingly we are tasked to comply with stringent greenhouse gas (GHG) regulations that focus specifically on reducing CO2 and other greenhouse gases such as methane and nitrous oxide (N2O). Current regulations cover the GHG emissions produced by the engine alone, on a tank-to-wheels (TTW) basis.

The chemical and physical properties of natural gas (predominantly methane) position it as a low carbon fuel for transportation. For every mega Joule (MJ) of energy released through the combustion of natural gas, approximately 25% less CO2 emissions are produced compared to combusting diesel or gasoline

Fuel type Fuel Carbon Content per Unit of Energy (gCO2/MJ) Percentage different in Fuel Carbon Content compared to NG








33% higher than CNG



29% higher than CNG

The information in the above table is taken from the GREET 2015 lifecycle emissions model maintained by Argonne National Labs.

All engines regardless of whether they are fuelled by diesel, gasoline, or natural gas, do not completely combust all the fuel that is supplied to the engine, but the unburnt fuel is generally <1% of the total fuel (i.e. greater than 99% combustion efficiency). In the case of diesel and gasoline engines, this unburnt fuel exists as tailpipe emissions of non-methane hydrocarbons. In the case of natural gas, the tailpipe unburnt fuel is predominantly methane, a greenhouse gas. These emissions must be taken into account when quantifying the GHG benefit of natural gas engines. In addition, certain NGV engine technologies can have an impact on engine and vehicle efficiency, which offsets some of the lower CO2 attributes of natural gas as a vehicle fuel.

Current and Future Technologies

We continuously look for technology solutions to simultaneously:

  • Improve engine efficiency (increase the amount of energy output per MJ of fuel energy input),
  • Reduce CO2 emissions, and
  • Reduce emissions of methane (using the most advanced combustion optimisation tools and techniques).

The ISL G Near Zero NOx 8.9L engine from Cummins Westport Inc. (CWI) scheduled for launch in 2016 will remove a significant source of methane emissions via the use of closed crankcase ventilation (CCV) technology.

Westport HPDI 2.0 technology, which is optimum for heavy-duty (HD) vehicles, includes further improvements to maximize the GHG benefits of natural gas. These include a closer match to the base diesel engine efficiency, careful optimisation of combustion to limit unburnt methane emissions to less than 0.2% of total fuel flow, and capture of regulator ventilation.

GHG Benefit Of Current Natural Gas Heavy-Duty Technology

GHG Benefit Of Current Natural Gas Heavy-Duty Technology

GHG = Greenhouse Gas
TTW = Tank to Wheel

For the CWI ISX12 G and ISL G Near Zero engines, the tailpipe CO2, methane, and N2O emissions were taken from Environmental Protection Agency (EPA) and California Air Resources Board (CARB) certification Executive Orders.

HPDI 2.0 attributes are based on Westport internal data. GHG benefits are calculated using the EPA specified methods applicable to Phase 1 GHG Regulations.

GHG Benefit Of Current Natural Gas Light-Duty Technology

GHG Benefit Of Current Natural Gas Light-Duty Technology

GHG = Greenhouse Gas
TTW = Tank to Wheel

Dedicated SI LD NGV data for CH4 and N2O emissions based on GREET 2015, with fuel efficiency relative to conventional gasoline scaled back from 103% to 100%. Enhanced SI NGV simulated with 115% fuel efficiency compared to conventional gasoline, consistent with GREET assessment of direct injection (DI) downsized turbo charged gasoline engines.

Westport’s North American products are certified in accordance with the relevant stringent regulatory requirements set by the EPA and CARB, and with the equivalent regulatory frameworks in place in our global markets. In many of these markets, engine emissions of both CO2 and methane (CH4) are measured and accounted for as part of the certification process, this ensures compliance with the latest GHG aspects of regulation.

With modest engineered enhancements, our product plans will see us fully compliant with even the strictest requirements of the newest CO2 regulations out to 2021 and beyond.

Production Emissions

As an engine and fuel system manufacturer, our direct responsibility is for the performance of fuels in the engines we develop and the emissions created by the engine. However, when any transportation fuels are used, it is not just the direct emissions that are factored in the decision. There are emissions that are generated in the production of all fuels (i.e. oil extraction, refining, electricity generation, natural gas processing and transmission). When these emissions are taken into account, a well-to-wheel (WTW) comparison can be made that includes the carbon intensity in producing, delivering, and combusting fuels.

Depending on the upstream production and supply chain energy and emissions characteristics, some of the low carbon benefit of fossil natural gas is reduced (from ~25% lower to ~17% lower than petroleum). However, transportation grade natural gas is increasingly being produced from non-fossil sources, in the form of renewable natural gas (RNG) or biomethane. Feedstocks for RNG include landfill gas (LFG), municipal solid waste (MSW), waste water treatment plants (WWTP), or agricultural manure.

In the case of these alternative natural gas feedstocks, substantial carbon intensity reductions can be achieved since turning these waste products into transportation fuel eliminates direct emissions of CO2 and methane that occur naturally and without any end-use benefit.

WTW Carbon Intensity of Fuels, Petroleum, Natural Gas and Renewable Natural Gas

WTW Carbon Intensity of Fuels, Petroleum, Natural Gas and Renewable Natural Gas

This chart shows the fuel carbon intensity on a per unit energy basis based on GREET 2015. For example, for 1 MJ of energy of CNG made from landfill gas and used in an engine, the total amount of CO2 (well-to-wheel) that results is about 85% lower than using 1 MJ of diesel. This chart addresses only the fuel, and as such does not take into account engine tailpipe emissions of methane, or any differences in engine efficiency.

When vehicle efficiency and tailpipe emissions are accounted for, RNG (in this case from landfill gas) can reduce the greenhouse gas emissions of natural gas heavy duty trucks by approximately 75% compared to the level produced from equivalent diesel trucks.

Heavy-Duty Truck GHG Reductions Using RNG From Landfill Gas

HD Truck - GHG Reductions

Landfill Gas fuel carbon intensity from GREET 2015 lifecycle emissions model maintained by Argonne National Labs.

The graphs shown here are illustrative, based on the assumptions within GREET 2015. However, the carbon intensity of renewable natural gas can be highly variable based on the type of feedstock, the geography, energy consumption to produce the biomethane, and the outcome for the feedstock if not used to make RNG.