TABLE 5-1 Projections of Domestic Production and Prices for Natural Gas and Diesel Fuel Price
|Production (quadrillion BTU)||24.59||32.57||38.37|
|Henry hub price ($)||2.75||5.23||7.65|
|Price delivered to transportation ($)||14.64||15.57||19.67|
|Diesel fuel price ($)||8.80||29.02||34.53|
NOTE: Prices are per million BTU in 2012 dollars. Note that a million BTU is equivalent to about 8 gallons of diesel fuel. Thus, natural gas costs on the order of $2.00 per gallon equivalent, much less than diesel fuel.
SOURCE: EIA (2013a).
have been incentivized for roughly 20 years in some states as part of emission-reduction programs. For MHDVs to use natural gas fuel, the most significant differences from current vehicles are the onboard fuel storage method and, for compression ignition (diesel-fueled) vehicles, the means of introducing and igniting the fuel in the engine. On-vehicle storage is either by high-pressure (3,600 psi is typical) CNG cylinders or by cryogenic containers filled with LNG. An illustration comparing on-vehicle storage of NG with diesel is shown in Figure 5-3.
For the same truck mission, the CNG tank plus fuel weighs about four times as much as a diesel tank plus fuel. LNG tanks and fuel weigh about twice as much as diesel. The cost of either CNG or LNG storage adds $40,000 to $50,000 to the cost of a heavy truck, but with the current low price of NG, the payback period for long-haul trucks is on the order of only 2 years.
There are three general technical classifications of NG engines, as shown in Table 5-2. Either CNG or LNG can replace gasoline with only modest changes to the spark ignition (SI) engine. Compression ignition (CI) engines are more complicated; NG can be used in combination with diesel fuel (dual-fuel); or it can supply all the energy to a high-pressure direct-injection (HPDI) CI engine, in which a small amount of diesel fuel is needed to achieve ignition.
Table 5-2 notes several advantages and disadvantages of each configuration.
FIGURE 5-3 Comparison of diesel and NG fuel tanks. SOURCE: John Wall, Cummins, Inc., “Opportunities and barriers for natural gas: Expanding natural gas in transportation,” Presentation to the Board on Energy and Environmental Systems on September 11, 2012.