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Modern commercial dual fuel engines operating in gas mode has the same level of fuel efficiency as the diesel mode. The NOx emissions level is reduced ten fold and satisfies the most stringent European 1/2 TA-Luft regulation. THC emissions can be controlled by the oxidation-catalytic process. High efficiency low NOx emissions gas engine performance is achieved by the following: Same power cylinder components as the basic diesel. Retarded timing together with short heat release duration by using Micropilot/Microcup designs. Lean lambda of 2.0 to 2.2. Minimal pilot fuel, 1% or less. Centrally located ignition if practical. Low air charge temperature at high load for high BMEP. 20-30% lower lambda at part load (compared to full load) achieved by compressed air bypass, skipfire, or variable geometry turbo. This paper provides only a qualitative treatise on gas engine combustion and the effects of fuel quality and engine design on combustion. Additional research is warranted.

The Fischer-Tropsch (FT) process can be used to synthesize diesel fuels from a variety of energy sources, including coal, natural gas and biomass. Diesel fuels produced from the FT process are essentially sulfur-free, have very low aromatic content, and have excellent ignition characteristics. Because of these favorable attributes, FT diesel fuels may offer environmental benefits over transportation fuels derived from crude oil. Previous tests have shown that FT diesel fuel can be used in unmodified engines and have been shown to lower regulated emissions. Whereas exhaust emissions reductions from these previous studies have been impressive, this paper demonstrates that far greater exhaust emissions reductions are possible if the diesel engine is optimized to exploit the properties of the FT fuels. A Power Stroke 7.3 liter turbocharged diesel engine has been modified for use with FT diesel.

Emissions from 10 refuse trucks equipped with Caterpillar C-10 engines were measured on West Virginia University's (WVU) Transportable Emissions Laboratory in Riverside, California. The engines all used a commercially available Dual-Fuel™ natural gas (DFNG) system supplied by Clean Air Partners Inc. (CAP), and some were also equipped with catalyzed particulate filters (CPFs), also from CAP. The DFNG system introduces natural gas with the intake air and then ignites the gas with a small injection of diesel fuel directly into the cylinder to initiate combustion. Emissions were measured over a modified version of a test cycle (the William H. Martin cycle) previously developed by WVU. The cycle attempts to duplicate a typical curbside refuse collection truck and includes three modes: highway-to-landfill delivery, curbside collection, and compaction. Emissions were compared to similar trucks that used Caterpillar C-10 diesels equipped with Engelhard's DPX catalyzed particulate filters.