NGV Environmental Benefits

NGV Environmental Benefits Natural gas is one of the cleanest burning alternative transportation fuels available today. Long recognized as an excellent fuel when used to generate electricity, heat homes, and fuel industrial facilities, natural gas is emerging as a leader in the alternative fuels marketplace.

Using natural gas as vehicle fuel helps the environment by positively affecting:

In addition, natural gas does not contaminate lakes, rivers, or groundwater as petroleum fuels do because it quickly dissipates into the atmosphere if a leak or spill occurs.

Commercially available medium and heavy-duty natural gas engines have demonstrated over 90% reduction in particulate matter and more than 50 percent reduction in nitrogen oxides (NOx) relative to commercial diesel engines. Natural gas engines also produce less greenhouse gases (CO2) that contribute to global warming.

See the Alternative Fuels and Advanced Vehicles Data Center (AFDC) for more information.

Energy Efficiency

Beyond the role of the fuel used in affecting CO2 emissions, the efficiency of the engine used affects the rate of CO2 emission. Obviously the use of more efficient engines results in greater fuel economy and associated lower CO2 emissions. Generally, diesel cycle engines Otto cycle. Spark ignition engines, which are in turn more efficient than gas turbine, jet engines. Use of any of these engines within hybrid cycles improves the overall efficiency of the system.

Different engines have different efficiency curves depending on the load on the engine. Hybrid engine efficiencies vary depending on the drive cycle of the vehicle. Vehicles used in stop and go urban applications where regenerative braking is used to capture and store braking energy show greater efficiency gains than vehicles used in highway transit applications. Natural gas hybrids are currently being used in a limited number of applications and promise impressive CO2 reductions.

Natural gas can be used in both spark ignition engines as well as diesel engines. Use of natural gas in a diesel engine generally requires a small amount of diesel fuel to initiate the combustion. This pilot fuel generally accounts for less than 1 percent to 20 percent of the fuel mixture depending on the load and the engine.

Engine/Fuel Combinations

By mixing various fuels with various engine cycles, you can quickly derive the optimum mix of engines, fuels, and technologies. An ultimate hybrid configuration would be to use a natural gas dual-fueled engine, piloted by biodiesel fuel, configured in a plug-in hybrid and would result in very low CO2 emissions. When the CO2 emissions of this configuration are compared with a hydrogen fuel cell, the overall "wellhead to wheel" CO2 emissions would be comparable to a hydrogen fuel cell vehicle, assuming that the electricity is derived from a fossil fuel.

Emission Comparisons

Over time, natural gas has effectively set the standard for the engine industry in demonstrating greater and greater emission reductions. As a result, diesel engine manufacturers have continually struggled to meet the emission performance of natural gas engines especially for NOx. No matter how clean diesel technology has become, natural gas engines have always remained lower in overall NOx emissions.

The attached table summarizes the relative emission attributes of various fuels and engine cycles:

More Benefits

Noise:

Noise emissions from natural gas fuel engines are less intrusive in the environment than noise from diesel engines. Noise from natural gas engines is generally not as loud and is less bothersome than the lower pitch rumble associated with diesel engines. Because natural gas engines don't emit the same degree of high energy sound waves as diesel engines, transit, school buses and refuse trucks operating in urban neighborhoods are likely to be less objectionable than their diesel equivalent. In addition, the lower pitched diesel rumble sound waves will travel further before dissipation than higher pitched noise and thus creates a greater noise footprint in the environment.

Worker exposure (air emissions, noise, and odor):

While most environmental assessments generally focus on the impact of emissions on ambient air quality, these reductions also limit worker exposure and improve the working environment.

Spills and ground water impacts:

Spills and leaks of liquid petroleum products (gasoline and diesel fuels) routinely contaminate surface water and groundwater.

Natural gas cannot contaminate these water supplies as it vaporizes into the atmosphere if released. The costs to build and operate spill prevention and control facilities are not generally considered in comparing traditional fuels against natural gas. As such it is a hidden, though very real cost to owners of facilities dispensing and using liquid petroleum products.