Research needs for future internal combustion engines

Transportation is second only to industrial use as the largest consumer of energy in the US and accounts for about 60% of our nation’s use of petroleum—an amount equivalent to all of the oil the country imports. The numbers are staggering: Some 10 000 gallons of petroleum are burned in the US each second of every day. Although new energy sources are being developed and renewable fuels are emerging to replace crude oil, improvements in the efficiency of internal combustion engines hold the promise of increasing our energy security and mitigating climate change. The environmental consequences and health hazards posed from urban smog and other combustion byproducts led to US regulation in the late 1970s designed to limit the emission of nitrogen oxides (NOx), hydrocarbons, and other pollutants from internal combustion engines. Controlling those emissions while maintaining high efficiency is a continuing challenge. In the last decade, a combination of improved combustion technologies and exhaust after-treatments has nearly eliminated those emissions from gasoline spark-ignited engines. Emissions from the more efficient compression-ignited diesel engines have proven more difficult to control. For example, catalytic converters are not practical for diesel engines because residual oxygen in the exhaust poisons the catalysts. For a review of internalcombustion basics, see the box on page 48. Standards continue to tighten, with new diesel emissions regulations taking effect in 2010. For consumers to continue benefiting from the high efficiency of diesel engines, meeting those new regulations is critical.