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The solution to reducing and eliminating the USA's demand for OPEC oil (i.e., 5 million of 13 million barrels per day of imported oil) touted by T. Boone Pickens is the conversion of America's 18-wheeler trucking fleet to natural gas. See The Daily Show: T. Boone Pickens Extended Interview, January 27, 2011 (USA) or The Daily Show: T. Boone Pickens Extended Interview, January 27, 2011 (Canada). Although not specified exactly how this would be done, Pickens suggested that it would involve the gradual replacement of old diesel trucks with new natural gas fueled trucks. At this time, both CNG and LNG-fueled trucks are available for this market but LNG vehicles have the advantage of potentially longer range but CNG has the advantage of more refueling stations.

T. Boone Pickens noted that natural gas costs $4/MCF which compares with about 7 gallons of diesel which would cost about $21 (see 13:35/22.20 of the extended interview). This does seems like an excellent price but, from a survey of natural gas and gasoline prices, Clean Energy Fuels Corporation (founded by Pickens) CNG & LNG stations seem to charge about $0.50/GGE less than the going price for gasoline. Pickens also goes on to say that the main thing that is keeping the USA from moving to natural gas is political leadership. There is no mention of fuel availability, which would seem to be a much bigger issue.

Before going farther, it would useful to put fuel prices in terms of the Diesel Gallon Equivalent (DGE), which means the amount of natural gas that has the equivalent energy of a gallon of diesel fuel. It compares with a GGE ( Gasoline Gallon Equivalent), which is how CNG is commonly advertised at CNG stations (see NGV Calcs). Using US DoE CTA Fuels Table data, the energy content of natural gas is 983 BTU/CF LHV, the energy content of reformulated gasoline is 113,602 BTU/gallon, while the energy content of low-sulfur diesel is 129,488 BTU/gallon LHV. The amount of BTUs in an cubic foot of natural varies from well to well (and pipeline to pipeline) but 983 BTU/CF is in the ballpark. Therefore, an MCF of natural gas works out to 7.591 gallons of low-sulfur diesel. Using the ratio between the energy content of reformulated gasoline and low-sulfur diesel, 1 DGE = 1.14 GGE.

Using Los Angeles as an example, CNG at Clean Energy Stations is currently selling for $2.60/GGE ($2.96/DGE) while diesel is selling for around $3.85/gallon - a savings of about $0.89/DGE. LNG at Waste Management stations in the Greater Los Angeles area seems to be selling for about $1.70/gallon or $2.95/DGE. If CNG were actually selling closer to the pipeline cost of natural gas, $4/MCF would cost about $0.527/DGE or $0.462/GGE. If we add $1/GGE for O&M costs and profit, CNG would be selling for about $1.462/GGE or $1.667/DGE.


While it's true that CNG/LNG can be a bargain for truckers if they can buy natural gas at the pipeline price, the company that seems to be most active in building CNG stations (Clean Energy Fuels) doesn't appear to be offering natural gas motor fuel at bargain prices. The gas utilities generally have very favorable CNG prices but very few seem to have any interest in promoting motor fuel. A trucking company could install its own CNG Fueling or LNG Fueling equipment to get bulk pricing for natural gas and this equipment has long been available. However, this only makes sense for trucks that return to a home base every day. Ideally, the natural gas motor fuel should be priced so as to yield a reasonable (maximum 2 year?) payback on the additional cost of the truck fleet's natural gas engine and refueling infrastructure.

The availability of a CNG/LNG engine depends upon whether the truck manufacturer offers the Cummins Westport engine and it appears that LNG has a limited availability in truck models. For long range vehicles, more natural gas may be stored onboard a truck as LNG rather than CNG. For those companies interested in moving their fleet to natural gas, the following manufacturers are commonly provide vehicles for the North American trucking industry:

Since there is no MSRP or performance data available for any of CNG or LNG trucks, one can only ask why manufacturers are so secretive. Does the CNG or LNG option carry a hefty premium that requires a substantial tax incentive to make these vehicles economically viable? If so, is the availability of LNG tax incentives (necessary to ultimately buy Clean Energy Fuels' natural gas) the political leadership that Pickens is looking for?

According to the AFDC Fuel Stations, there are only 40 LNG stations in the entire USA, with the vast majority (32) being in California. This compares with 873 CNG stations, with the majority (215) being in California. Therefore, the drive to replace OPEC oil with natural gas has to start in California and most likely in the Greater Los Angeles area.


The availability of a natural gas fueled engine in a North American heavy or medium duty truck pretty much depends upon whether the truck manufacturer offers Westport products in its engine options. Westport has 4 business units offering alternative fuel products:

For these vehicles, the choice is between dedicated CNG/LNG engines (Cummins Westport) and dual fuel CNG/LNG engines (Westport HD).

The latest spark-ignited, natural gas engine offered by Cummins Westport is the ISL G (based on the Cummins ISL9 8.9L engine) but the Cummins Westport C Gas Plus (based on the Cummins ISC 8.3L engine) and the Cummins Westport B Gas Plus (based on the Cummins ISB 5.9L engine) are also available. The Cummins Westport ISL G engine achieves low emissions with stoichiometric combustion with cooled EGR and a three-way catalyst (TWC).

The latest dual fuel, diesel-natural gas engine offered by Westport HD is the ISX G, which is based on the Cummins ISX15 15L engine). The ISX G engine uses direct injection of gas into the combustion chamber and relies on a pilot injection of diesel fuel to ignite the natural gas. Although not specified exactly (and likely varies with engine speed and load), the ISX G uses extremely low amounts of diesel fuel (~5% on an energy basis) for the pilot injection. From Cummins' emission brochures, the ISX G engine also uses cooled EGR but with Select Catalytic Reduction (SCR) and Diesel Particulate Filters (DPF).

The incremental price of the ISL G and the ISX G engines options are not readily available, nor are their expected fuel consumptions. In his thesis paper " The Role of Natural Gas as a Vehicle Transportation Fuel ", Paul Murphy reports that the LNG ISL G engine adds about $40,000 to the price of a diesel truck while the LNG ISX G engine adds about $100,000 (see p 48). Since the ISL G operates with a throttle and has a lower compression ratio than the ISL9 diesel engine, its diesel-equivalent LNG fuel economy should likely be lower than the diesel-only ISL9.


In Europe, Volvo Trucks has an diesel-LNG dual fuel truck that was field-tested by a few fleets in the UK and in Sweden in 2010. Rather than direct-injecting natural gas into the combustion chamber, Volvo uses port injection at the intake manifold to produce a premixed natural gas fuel mixture that is ignited by a pilot injection from the diesel injectors. They plan to have limited numbers of diesel-LNG available for sale starting in 2011. Please remember that "gas" used in the videos below refers to methane rather than gasoline.

Please notice in the first video (by TheAutoChannel) that Volvo also uses a two line fill procedure (see video 0:22 to 0:32), which has significant advantages over single line fills to eliminate vehicular LNG issues. The vent line is the orange line to the right of the fill line and you can see a second operator replacing this line on the LNG dispenser when refueling is completed.


As mentioned earlier, dedicated LNG-fueled trucks (like those that use Cummins Westport engines) are now available from the factory, they have a limited range because the LNG tanks hold less energy than their diesel equivalents. This implies that they also require that the trucks return to their yards to refuel because LNG is not readily available in North America. The alternative is use a diesel-LNG dual fuel system (like the natural gas EcoDiesel System) that supplements diesel fuel with LNG, and the typical substitution rate is very conservatively about 30%. That would mean that a truck with 200 gallons of diesel capacity would require an LNG tank holding about 60 DGE (Diesel Equivalent Gallons) or about 104 gallons of LNG. This would extend the range of the truck approximately 40-45%. Alternatively, if a truck had a pair of 120 gallon diesel tanks (26" x 52" each), the replacement of one diesel tank with a 72 gallon (26" x 52") LNG tank would result in slightly reduced range (~70% of 240 gallon range) but with a significantly lower cost per mile. These systems seamlessly revert back to 100% diesel operation when the natural gas tank reaches empty so running out of natural gas never leaves you stranded. Much higher substitution rates are possible because the EcoDiesel System is fully programmable but this requires chassis dynamometer tuning for optimization. The LNG tank (typically 26" in diameter) will add about $14,000 to the cost of a diesel-LNG conversion, with higher capacities costing very slightly more on account of the added material cost for the increase in length. Installation would add about $1000 to the cost of conversion so that the overall cost of converting any diesel truck to LNG would be less than $18,000 per truck.

EcoDiesel System - Natural Gas

 

EcoDiesel System - Natural Gas