Low Emissions Class 8 Heavy-Duty On-Highway Natural Gas and Gasoline Engine

The goal of this project was to demonstrate that a Mack E7G engine operating stoichiometric with Exhaust Gas Recirculation (EGR) and a three-way catalyst can meet the 2010 emission standards for heavy-duty on-highway engines. Results using natural gas and gasoline as the fuel are presented. The Mack E7G is currently a lean burn natural gas fueled engine, which was originally derived from the diesel engine. The calibration of the lean burn engine was modified to operate as a stoichiometric engine. An EGR system and a three-way catalyst were added to the engine. One of the lean burn natural gas ratings for this engine is 242 kW at 1950 rpm and 1424 N-m, at 1250 rpm. This rating was also used for the stoichiometric natural gas engine. Transient emissions and 13-mode steady-state emissions tests were conducted on the engine on natural gas. The engine meets the transient emission standards for 2010 for NO_x, NMHC, and CO on natural gas. Steady-state results on the 13-mode test show this engine meets NO_x, NMHC, CO and particulate matter emissions standards for 2010 on natural gas. Formaldehyde emissions are well below the ULEV and transient bus standards for heavy-duty vehicles on both the transient and steady state tests. Efficiency of the natural gas stoichiometric engine was comparable to a typical low emissions lean burn natural gas engine. Results with gasoline were conducted on the first seven modes of the 13-mode steady state test. The engine did not meet the emissions standards for 2010 on gasoline for this testing. Catalyst degradation from misfires while setting up the engine to operate on gasoline contributed to the higher than expected emissions.