Compressed Natural Gas (CNG): The Most Practical Low-Smog Engine Fuel

Compressed Natural Gas (CNG): The Most Practical Low-Smog Engine Fuel

The use of natural gas as a transportation fuel currently has several advantages over gasoline and diesel: operations cost, reduction of engine wear-and-tear, much lower carbon emissions, lower pollutants, and now even lower smog-producing NOx pollutants. NOx pollutants refer to nitrogen oxides: NO2 (nitrogen dioxide), N20 (nitrous oxide), and NO (nitric oxide). All three are implicated as the major contributors through combustion reactions, to ground-level, or tropospheric ozone, also known as smog or photochemical smog. In addition, N2O is a significant greenhouse gas. 

The new Cummins Westport Natural Gas Engines could have positive implications for places like Los Angeles, California that are prone to smog. These engines are the lowest NOx producers so far of any internal combustion engines. The technology is available now. Peterbilt announced at the end of August 2016 that it will be offering the Cummins Westport Natural Gas Engines in three of their 2017 models. Torque and power performance is expected to be comparable to diesel models. 

The major hurdle to CNG vehicles is initial up-front cost. The state of California has more stringent emissions standards than the rest of the country largely due to the susceptibility to smog. Therefore, California will be the first area where these low NOx engines will be widely utilized. As Oil and Energy magnate T. Boone Pickens points out there is a great opportunity for natural gas to be utilized in over-the-road trucking throughout the U.S. Infrastructure, basically gas stations that sell compressed natural gas (CNG), has been growing throughout the U.S. and NGV short-haul and long-haul trucks continue to penetrate the vehicle market, although at a much smaller rate than it could be. Pickens thinks that some of the massive fraud fines to be paid by Volkswagon should be used to promote NGVs. Although I don’t always agree with Pickens I think he has a great idea here. There is a sense of justice to it – it would be a great way to directly use funds from emissions penalties to reduce emissions in the most practical and inexpensive manner. Sure, one could do it with EVs but the costs are too high compared to NGVs and additionally the EVs are often powered by grid coal which makes their life-cycle emissions greater than NGVs. Initial upfront costs are recouped in lower fuel costs as well as low-maintenance natural gas engines since wear-and-tear on some engine parts is far less and catalytic converter maintenance is not an issue. 

Technically, the cleanest lowest life-cycle emissions form of transport would be an EV powered with renewable energy but renewables are scarce on the power grids so in reality in most cases it would be an ultra-low emissions CNG powered with biogas, aka. renewable natural gas (RNG). Of course, RNG is a limited resource compared to fossil fuel natural gas so buying RNG exclusively is impractical unless one finds access to a secure source. Refuse truck fleet vehicles have led the charge to fueling with landfill RNG since the same companies may own the landfills as well as frequenting them. UPS announced in Dec. 2015 a deal to fuel its fleets in Memphis Tennessee and Jackson, Mississippi with landfill biogas. RNG there will fuel 140 fleet vehicles. UPS fuels 3800 vehicles with natural gas worldwide (as of Dec. 2015). Ryder also announced a deal in Nov. 2015 to fuel with RNG at two RNG fueling stations in southern California with Clean Energy Renewables providing maintenance and supply for their fueling stations. Fueling heavy duty vehicles with natural gas in ultra-low emissions engines has the potential to reduce pollution in high-smog areas and to decrease greenhouse gas emissions and other pollutants as well. Companies such as Unilever are geared toward reducing environmental impact for both social and financial reasons and using RNG and CNG is one very clear and important means to do so. 

   

Natural Gas engines run quieter, the fuel is currently cheaper than gasoline or diesel (and likely to remain so), engine maintenance is lower, engine life is longer, engine performance is adequate, emissions are lower, smog-producing NOx emissions are near-zero, and there are some government incentives for switching. Currently, natural gas fuels about 3% of the national medium and heavy-duty transportation fleet, 35% of the transit bus fleet, and 55% of the refuse truck fleet. According to the DOE there are about 150,000 NGVs on the road in the U.S. so the current market share is quite small. According to Chuck Feinberg of the New Jersey Clean Cities Coalition “Natural gas is the cleanest alternative-fuel vehicle available today for medium and heavy-duty vehicles.”

In addition to CNG there are also LNG (liquified natural gas) vehicles and some can utilize both. While vehicles that run on LNG are more expensive they can travel longer distances without refueling since the gas is stored as a liquid. Overall though, CNG has less environmental impact since LNG requires energy for liquefaction. Additional CNG tanks can be added but that does increase weight as well as reducing cargo area. Thus, driving range is a small issue but is considerably more than EV driving range. Fueling time was once an issue but fueling now is much faster.  

EVs cost 3 to 4 times as NGVs. Thus fleet conversions to NGV can offer vast advantages compared to conversions to EVs in NOx emissions reductions since more 3-4 times more vehicles can be converted at the same cost. Thus NGV fleet conversions can reduce city smog faster and cheaper than EVs by taking more higher-emitting vehicles off the road. NGVs are a cheaper and faster way to reduce NOx and other emissions than EVs.

There are or at least were some significant issues with methane leaks from NGVs and NGV fueling stations. However, new leak reduction technologies have reduced them very significantly. Although leaking methane is not a pollutant that affects air quality it is a powerful greenhouse gas. Such leakage is one reason lifecycle emissions of NGVs are not lower on past tests. Although they were significantly lower than diesel lifecycle emissions, they are now much lower than they were. A recent study by the West Virginia University Center for Alternative Fuels, Engines, and Emissions noted methane leak reductions successes by the NGV industry:

“The findings confirm that many of the technologies being deployed on the latest generation of natural gas engines and refueling infrastructure are dramatically lowering emissions and continue to make natural gas the ‘greenest’ choice for fleets across North America.”

NGV America explained the methane emissions reductions which include closed crankcase systems:

“Today’s natural gas vehicles provide significant environmental benefits including the lowest emissions of nitrogen oxides (NOx), particulate matter and other pollutants that directly affect public health. Additionally, the latest engines (which were not among those studied as part of this research) include closed-crankcase systems and other upgrades that optimize operation and increase efficiency. For these new spark-ignited natural gas engines, these changes have resulted in a more than 70 percent reduction in methane emissions compared to engines produced only a few years ago.”

Less than 20% of the methane leaks in the study were coming from the fueling stations and those leaks have also been addressed:

“New technologies and best practices at CNG and LNG stations with dispensers, compressors, boil off gas management systems for storage tanks, and other equipment are lowering these emissions even further and the study provides a solid baseline to demonstrate future improvements.”

NGV America also estimates that 20-30% of natural gas used for transportation is RNG/biogas. EPA classifies RNG as cellulosic biofuel and notes that RNG represents the largest share of cellulosic biofuel sold in the U.S. today.

References:

‘Near-Zero NOx’ Natural Gas Engine from Cummins Westport is On the Way - by John O’Dell, in Forbes (Autos), April 11, 2016

Air Quality and Climate Protection Goals Can Be Immediately Addressed Most Effectively with Ultra Low Emission Heavy-Duty Natural Gas Engine Technology and Renewable Natural Gas Fuel, Technical White Paper Finds – posted at Clean Energy

Next Generation Heavy-Duty natural Gas Engines Fueled by Renewable Natural Gas – NGV Game Changer Technical white Paper (ngvgamechanger.com)

How Volkswagon is Shaping America’s Energy Future – by T. Boone Pickens, in LinkedIn, March 10, 2017

UPS to Power Memphis and Jackson Alternative Fuel Fleet with Natural Gas from Landfills – at UPS.com, Dec. 18, 2015

Ryder to Fuel Fleets with Renewable Natural Gas – fleetowner.com, Nov. 12, 2015

Natural Gas, the Other Alternative Fuel for Transportation Sector – by Tom Johnson, in New Jersey Spotlight, Feb. 15, 2017

Peterbilt Introduces Cummins Near-Zero Engine for Select Models, in Next Gen Transportation News, Aug. 30, 2016

U.S. Dept. of Energy – Alternative Fuels Data Center – Natural Gas Vehicles

Fact Sheet: Natural Gas Vehicles’ Emissions Data and Comparisons – Northwest Gas Association

NGV America Applauds Collaborative Approach of New Study That Identifies Opportunities for Improving on Emissions Benefits of NGVs – press release form NGV America, Jan. 5, 2017