Addition of Exhaust Gas Recirculation Onto a Large-Bore, Two-Stroke Natural Gas Engine, and its Effects on Fuel Consumption, Emissions, and Combustion

Abstract

The focus of this research was to examine the effects of adding exhaust gas recirculation (EGR) on a large bore 2-stroke, lean-burn natural gas (2SLB) engine in its stock configuration, using a previously determined optimal spark plug. EGR has been a common emissions reduction technology used for on-road gasoline, natural gas, and diesel fueled vehicles. EGR — both cooled and uncooled — is found in nearly all on-road and many off-road engines. The optimal spark plug was found in other research and it was tested with various rates of EGR. The test platform was a 1971 Cameron AJAX-E42 single-cylinder engine — common to the natural gas industry. The engine had a bore and stroke of 8.5 × 10 inches, respectively. The engine displacement was 567 cubic inches with a trapped compression ratio of 6:1. The engine was modified to include electronic spark plug timing capabilities along with a mass flow controller to ensure accurate fuel delivery. Each EGR configuration was examined at spark timings of 14, 11, and 8 CAD BTDC. Tests were conducted using an air-cooled, eddy-current power absorber at an engine speed of 525 RPM and load of 400 1b.-ft. of torque. Due to its large thermal inertia, the engine was operated for three hours prior to data collection to ensure representative and operation. In-cylinder pressure data were collected using a piezoelectric pressure transducer at increments of 0.25 CAD. Various levels of EGR and spark timing conditions were evaluated against engine performance including both regulated and unregulated exhaust emissions. Volumetric EGR rates of 2.5% showed reduced NOx emissions and improved fuel efficiency while rates of 5% did not yield NOx reductions.