The LNG Compromise
The internal combustion engine (ICE), while not the most efficient from a thermodynamic perspective (even the best engines lose more than 70% of their energy to heat), are still the most widely adopted form of power source in modern vehicles. There are two distinct designs for ICEs; the gasoline engine and diesel engine. Generally, the design of a diesel engine allows for higher thermal efficiency, increasing the work and engine can produce and bettering fuel economy.
The problem with ICEs stem from the combustion of the components that power them. Gasoline and Diesel fuel have additives that are released into the atmosphere via automobile exhaust pipes, along with carbon dioxide and products of incomplete combustion; carbon monoxide and the ozone damaging family of nitrous oxides (NOx). Electric vehicles promise a reduction on these dangerous emissions by eliminating the individual combustion components on each vehicle.* The drawback to electric engines is that they cannot currently produce enough power to effectively haul loads like a heavy duty tanker truck or 18-wheeler like an ICE can. Electric vehicles require special stations on which to recharge their power; not ideal for cross-country transport, and the battery technology has not yet yielded a battery feasibly small enough that can produce sufficient power to haul heavier loads.
Liquefied Natural Gas (LNG) could be a viable stepping stone in establishing greener vehicles for the future. Unlike gasoline and diesel, LNG is a pure hydrocarbon mix of predominately methane with some ethane and burns quite cleaner than the traditionally fueled vehicles of today. There are still emissions from incomplete combustion and fugitive leaks, but many of the constituent chemicals present in gasoline/diesel are not present, as LNG must be nearly purified for it to be effectively transported in tankers and pipelines (which requires cooling and pressurization to liquefy) and before domestic use in households. An additional benefit is that most ICE automobiles can be retrofitted to burn natural gas as its primary fuel source and existing infrastructure can more easily be re-purposed to distribute natural gas.
The United States is now a net exporter of LNG and third in production to only Australia and Qatar. An expansion of pipelines in the continental US and increased investment in non-pipeline transport have allowed for broader domestic use of LNG. The increased utility use of LNG for electric energy production and the usefulness of LNG in downstream chemical production signals a positive outlook in continued investment in LNG and in taking steps towards a future of clean energy.
*Electric energy is largely supplied by electric power generating stations that use steam turbines driven by the combustion of fossil fuels. Although there are still emissions from these sources, it becomes a less futile task if a single area source of emissions can be considered as opposed to miniature combustion sources in transit en masse.
