Shale Gas Will Rock the World: Huge discoveries of natural gas promise to shake up the energy markets and geopolitics, said the Wall Street Journal in a recent feature. New technology allowing extraction of natural gas from shale will be a game-changer, hindering short-term development of energy alternatives but fueling power station expansion needed for electric cars. Not only is shale gas an abundant North American resource, but natural gas is the cleanest burning of all the hydrocarbon fuels.
While this article does not talk about the direct use of natural gas as an energy source for automobiles, Edison2 has given thought to this approach.
Based on our preliminary analysis we think natural gas can work well as an automobile fuel, but with drawbacks. There may be added wear on the valve train and rings in the absence of fluids passing over them. Compared to liquid hydrocarbons the efficiency and power output of natural gas is less. Natural gas has no charge cooling, and displaces a portion of the incoming air charge in the cylinder, resulting in about a 10% decrease in power output; because this decrease occurs without a proportional reduction in friction, efficiency suffers.
But natural gas has some advantages. It has excellent knock resistance at 120-137 octane. Natural gas has good lean-burn behavior and high EGR tolerance. Because there is no wall wetting, cold start and transient issues should disappear. We think we may be able to run the engine at higher boost levels with natural gas and make up for the reduced specific power output.
Of course the use of natural gas for automobiles is not a new idea, having been used since the 1800’s. In other parts of the world, such as South America and Asia, natural gas cars are commonplace, especially in flex-fuel configurations, while in the US natural gas is mostly found in commercial vehicles and fleets. The Honda Civic GX is the only natural gas car available in the US.
Natural gas has other positives for the US. Use of natural gas for transportation decreases our reliance on imported oil and supports the domestic economy. Many homes already are connected to natural gas. Combined with a small compressor this offers the possibility of filling up at home.
Combined with a car of the efficiency of the Very Light Car we could see a range of 1000 miles or more. Efficiency of this magnitude would minimize the need for new refueling infrastructure, dovetailing easily with the infrastructure already being built for trucks.
The question of which power source is the most efficient and least polluting has no single answer. All choices have advantages and drawbacks. Coming soon: why Edison2 chose E85 for the Very Light Car in the X Prize competition.