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Abstract

Dual fuel engines are being utilized more due to stricter emission standards, increasing diesel fuel cost, and decreasing natural gas cost. These engines are originally sold as diesel engines. They are converted to dual fuel operation with an aftermarket dual fuel kit. Natural gas is blended with the intake air. As this occurs the amount of diesel used is reduced. The maximum natural gas substitution is limited by knock or emissions of carbon monoxide (CO) and total hydrocarbons (THC). In this work a John Deere 6068H diesel engine is converted to operate as a dual fuel engine. The engine is a tier II 6 cylinder, 6.8 liter, 4-stroke compression ignition engine with a compression ratio of 17:1 and a power rating of 168 kW at 2200 rpm. This work aims to evaluate emissions and efficiency of a diesel derivative dual fuel engine. A natural gas fuel system was installed to deliver fuel upstream of the turbocharger compressor. The engine was operated at 1800 rpm through five different load points in diesel and dual fuel operating modes. Fuel consumption and pollutant emissions were measured. Elevated carbon monoxide and hydrocarbon emissions were observed at low loads for dual fuel operation. Overall CO and THC emissions increased for dual fuel operation. However, particulate matter (PM) and nitrogen oxides (NOx) on average were significantly decreased.