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This paper reports some results from a study of emissions control for railway locomotives performed for the California Air Resources Board.(1)* Feasible and cost-effective control techniques for locomotive emissions include retarding injection timing and other engine modifications, selective catalytic reduction (SCR), use of liquified natural gas (LNG) fuel with low-emission dual-fuel or spark-ignition (SI) natural gas engines, LNG combined with SCR, and electrification. Use of a combination of dual-fuel and SI LNG engines could reduce locomotive NOx emissions by 80%, at a cost of less than $1,100 per ton of NOx eliminated. SCR added to diesel and LNG could produce NOx emission reductions of 90 and 97 %, respectively, at costs less than $3,300 per ton. All of these technologies could be retrofit to existing diesel locomotives.

Diesel engines in mobile off-highway applications include those used in railway locomotives, marine vessels, farm equipment, construction and industrial equipment, and mobile refrigeration. Engines in these five classes are responsible for about one-third of all mobile diesel emissions (highway vehicles account for nearly all of the rest). Emissions from these engines are not presently subject to regulation. This paper presents estimates of emission factors and nationwide emissions inventories for each of these equipment classes. Estimates of achievable emissions levels, the technologies required to achieve them, and the cost-effectiveness of emissions control for each class are also presented. Emissions test procedures and recommended regulatory approaches for controlling off-highway diesel emissions are discussed as well.