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Gaseous-Based Alternate Fuels

The use of alternative and advanced fuels is critical for reducing GHG emissions and improving air quality.

Important obstacles stand against the adoption of innovative technologies, of which one of the most important is the lack of practical information coming from independent sources. The objective of these fact sheets is to inform those in the trucking industry about new and emerging advanced technologies that have been tested through the Energotest program (run by FPInnovations), which can help increase fuel efficiency and, at the same time, reduce the environmental impact of freight transportation in Canada.

Description

This fact sheet will focus on gaseous-based fuels that are currently used in freight applications, such as natural gas and liquefied petroleum gas (LPG). Other fuels such as dimethyl ether (DME) and hydrogen, which are not yet ready for implementation, are briefly presented.

LNG truck (Courtesy of Westport Innovations)

 

Natural Gas

Natural gas has environmental benefits compared to some other fuels and it can be stored onboard in high-pressure reservoirs as compressed natural gas (CNG), or in special cryogenically cooled vacuum-insulated tanks as liquefied natural gas (LNG). For a given tank size, LNG, being in a liquid state, can hold more fuel than CNG, which holds its fuel in a gaseous state. Dedicated natural gas vehicles are designed to run only on natural gas, while dual-fuel engines have two separate fuelling systems allowing the vehicle to use either natural gas or a conventional fuel (gasoline or diesel). Most heavy-duty LNG engines are dual-fuel diesel engines: during normal operation of LNG engines, 95% of the fuel burned is natural gas, while 5% is diesel fuel which serves as a pilot for combustion and when idling.

Natural gas can also be used in diesel fumigation. The fumigation system injects the gas into the intake air stream of a diesel engine.

Combustion of natural gas engines produces 20% less greenhouse gas (GHG) emissions and up to 50% less noise. The main disadvantage of natural gas is the lack of fuelling infrastructure in Canada.

Natural gas costs less than diesel fuel: the overall price of LNG energy equivalent is almost half of diesel, but for a given tank size, the tanks will only contain enough fuel to travel half of the distance that regular diesel fuel would provide.

Because of low production volumes, natural gas vehicles cost significantly more than diesel-fuelled vehicles: the premium is roughly $40 000 for CNG and $80 000 for LNG tractors. According to the International Association of Natural Gas Vehicles, natural gas has a strong potential as a motor fuel because it is abundant and, through the production of biogas, may be a renewable resource.

Transport Robert, a partner of Program Innovations Transport (PIT), is planning to buy 180 LNG Peterbilt highway tractors powered by 15-L Westport GX engines between 2010 and 2013. The company is cooperating with Gaz Metro, the distributor of natural gas in Quebec.

LPG

Liquefied petroleum gas (LPG), also known as propane, has been used in vehicles since the 1920s. Today, more than 13 million vehicles worldwide run on propane, and they produce 12% fewer GHG emissions than gasoline and considerably less nitrogen oxides (NOx) and particulate matter than diesel. Propane is the third most widely used motor fuel in the world, after gasoline and diesel fuel, and it comes with an existing and affordable fuelling infrastructure. Propane-powered lift trucks represent 60% of all material handling vehicles and 80% of all internal combustion lift trucks.

Most LPG engines are converted gasoline engines and they operate on the Otto cycle (spark ignited). Dedicated LPG vehicles are designed to run only on propane, while dual-fuel vehicles have two separate fuelling systems that enable the vehicle to use either LPG or gasoline. The fuel efficiency for dual-fuel vehicles is comparable to that of gasoline vehicles, but the fuel efficiency of dedicated LPG vehicles is generally less than gasoline vehicles because propane has lower energy content.

For dual-fuel diesel-LPG vehicles, LPG is injected into the intake air stream, usually up to 35%. This approach has been successfully used in agricultural machines for many years. In the United States, Texas and Colorado have accepted diesel-LPG as an alternative fuel.

Recent studies have examined dual-fuel diesel-LPG vehicles and found that fuel consumption and smoke emissions are reduced, but hydrocarbon emissions are increased.

DME

Dimethyl ether (DME) is a synthetic fuel that was initially obtained from natural gas or coal. Recent studies concluded that DME can be commercially produced from cellulosic biomass and industry by-products, such as paper pulp and black liquor. The production process seems to be simpler and the final product would cost less than petrodiesel or biodiesel. DME has a high cetane number (55 compared to typical values between 42 and 45 for diesel); it is sulphur-free, and produces less carbon monoxide, particulate matter, and nitrogen oxides compared to petroleum-based diesel engines. Although the energy density of DME is lower than diesel, the engine thermal efficiency is higher. DME is also relatively non-toxic, although it is highly flammable. DME is known to adversely affect many types of plastics and rubbers; it was found that metal-to-metal seals using non-sparking metals would be the most effective type of seal for engines using DME. However, the technology is not yet ready for implementation.

Fuel Cells and Hydrogen

A fuel cell vehicle is powered by electric motors, which use the electricity produced by the fuel cell from hydrogen. Fuel cell vehicles are more efficient than conventional internal combustion engine vehicles and their only emission is water. The BC Transit fleet used 20 fuel cell buses during the 2010 Olympics and Paralympics Winter Games.  This technology is still in development, and also not yet ready for implementation.

Another possibility for using hydrogen in diesel engines is represented by hydrogen onboard generators. Hydroxy gas, a mixture of hydrogen and oxygen, is produced through electrolysis of distilled water and is injected into the engine's air intake where it is mixed with the incoming air. Manufacturers of such systems claim increased fuel efficiency and lower emissions. However, FPInnovations has tested systems from four different suppliers which did not show any reduction in fuel consumption. Apparently, the problem with onboard hydrogen generators is that the process is not efficient so far: the energy obtained from burning the hydrogen is not enough to overcome the energy required to produce the gas.

Scope

Natural gas engines are available in various sizes, suitable for class 6, 7 and 8 trucks and buses. LNG fuel systems are typically installed on heavy-duty vehicles, while CNG engines are being used for medium-duty vehicles.

Propane engines can be used as original equipment or retrofitted on light-duty vehicles, in short-haul applications for Class 6 and 7 vehicles, and on machineries.

Return on Investment

The return on investment of alternate-fuelled vehicles should be based on the payback period: how long does it take for the fuel savings to pay for the increased capital costs. For consumable items, such as an engine, the payback period must be reached before the service life is consumed for it to be considered a worthwhile investment.  Other considerations include repair and maintenance costs, and any potential benefit that may result from reduced GHG emissions. In operations where the trucking company is considering setting up its own fuelling system, the cost of these systems should also be taken into account.

Most of the information used for the calculation has been provided by engine manufacturers and is general in nature. It has not been verified by third-party testing.

The following is an example of a payback calculation for a CNG-fuelled Class 8 vehicle:

• We consider a five-axle tractor/semi-trailer combination working local pick-up and delivery, with an annual mileage of 100 000 km.
• The increased cost of a CNG-fuelled engine compared to diesel is $40 000. This includes the engine and CNG fuel tanks and system.
• Diesel fuel price is $1.10/L, and CNG price is $1.17/kg. Considering that 0.75 kg natural gas contains the same amount of energy as 1 L of diesel, the equivalent unitary cost would be $0.88.
• Fuel consumption with diesel is 28 L/100 km.
• Annual diesel fuel cost would be:  
• Annual CNG cost would be:  
• The annual savings would be: $30 800 - $24 640 = $6 160
• The payback period would be: $40 000 / $6 160 = 6.5 years

The extra costs of the CNG engine would be paid back in 6.5 years. This example assumes the same efficiency and energy usage for both engines.

Issues to Consider

Natural Gas

• There are no commercial fuelling facilities for LNG in Canada: implementing LNG-fuelled vehicles would also require the creation of fuelling facilities.
• Natural gas and compressed natural gas contain an odorant (mercaptan) so leaks can be easily identified by smell. The liquefied natural gas does not contain this odorant and is therefore odourless. Sensing equipment is required at service facilities to identify leaks.
• For natural gas engines that use diesel for ignition, in the event that the natural gas tanks are empty, the engine can still operate on diesel, but at significantly reduced power.
• Releasing 1 kg of unburnt natural gas into the environment is the same as releasing 19 kg of CO2.
• Natural gas is less dense than air, and leaking gas tends to disperse into the atmosphere.

Propane

• Propane is readily available and there is an extensive fuelling infrastructure already in place.
• Propane is denser than air: leaks could cause gas to accumulate at ground level.
• Ventilation and sensing equipment are required at service facilities to identify and dissipate leaks.

Specification Considerations

LNG, CNG, and LPG engines are available from a variety of original equipment manufacturers (OEMs) that manufacture vehicles for a variety of different applications.

Natural gas engines are available in various sizes, and suitable for class 6, 7 and 8 trucks and buses. LNG fuel systems are typically installed on heavy-duty vehicles with a longer operational range. CNG engines that operate on the Otto cycle (spark-ignited) are being used in short-range, centrally fuelled vehicles such as refuse trucks, concrete mixers, straight trucks, and school buses.

Propane engines can be used on short-haul applications for Class 6 and 7 trucks, buses, forklifts, and passenger vehicles.  Retrofit kits are available for existing equipment.

Regulatory Issues

Currently, Quebec is the only province in Canada that has incentives for natural gas powered vehicles. They can be depreciated at a faster rate, providing tax savings for the owner.

U.S. Environmental Protection Agency regulations limiting idling of diesel engines do not apply to natural gas engines.

Maintenance Considerations

Natural gas and propane are unlike diesel fuel, and special precautions must be taken during maintenance operations. Some of these include:

• Mechanics require specialized training and certification to work with the gaseous fuel systems
• LNG fuel tanks will vent to relieve internal pressure as the temperature of the LNG rises and it turns from liquid to gaseous form. Therefore, it is recommended that vehicles be stored outdoors.
• If vehicles are to be stored indoors, special gas sensors and ventilations system are required. CNG tanks are also subject to venting, but not to the same degree as LNG tanks.
• For longer term storage, in excess of 7 days, it is recommended that LNG tanks be emptied to avoid excessive venting.
• Maintenance specific to the gaseous fuel system is required annually. This includes replacing filters, and inspecting hoses and gas detection systems.

References

Bradley, D. 2010. LNG can serve niche in strategy to reduce GHG from trucks. Truck News, August 2010.

FPInnovations. 2007. Energy Efficiency Newsletter, January 2007, Pointe-Claire, QC.

FPInnovations. 2010. Energy Efficiency Newsletter, September 2010, Pointe-Claire, QC.

Surcel, M.-D. 2007. Energotest 2007 : Accelerated Fuel Consumption Tests for Evaluating Potentially

Ecoenergetic Technologies. FPInnovations, Pointe-Claire, QC. Internal Report IR-2007-11-28. 119 p.

Surcel, M.-D., Michaelsen, J., Brown, M. 2007. FERIC’s Energy Efficiency Research program. The 3rd Forest Engineering Conference (FEC), October 1-4, 2007a. Mont-Tremblant, QC.

Surcel, M.-D. 2010. Energotest 2010: Fuel consumption track tests of fuel-saving technologies. FPInnovations, Pointe-Claire, QC. Internal Report IR-2010-10-28. 93 p.

Tinham, B. 2010. Gas guzzlers? Transport Engineer, May 2010.

United States Department of Energy. 2010. Natural gas basics. DOE/GO-102010-3068 - April 2010. Energy Efficiency and Renewable Energy, Vehicle Technologies Program, Washington, DC.

United States Environmental Protection Agency. 2002. Clean alternative fuels: Liquefied natural gas.

EPA420-F-00-038. Transportation and Air Quality, Transportation and Regional, Programs Division Washington, DC.

Web sites:

Cummins Westport Inc. official Web site. http://www.cummins-westport.com/ (accessed Nov. 30, 2010).

U.S. Environmental Protection Agency (EPA). Greenhouse gas equivalencies calculator.
  http://www.epa.gov/cleanenergy/energy-resources/calculator.html (accessed Nov. 29, 2010).

Propane Gas Association of Canada official Web site.
http://www.propanegas.ca/PGAC/Environment_ClimateChange.asp (accessed November 29, 2010).

Terasen Gas official Web site. http://www.terasengas.com/Homes/default.htm (accessed Nov. 30, 2010).

Westport Innovations Inc official Web site. http://www.westport.com/ (accessed Nov. 30, 2010).

Date modified:

2012-03-12

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