Precombustion Chamber NOx Emission Contribution to an Industrial Natural Gas Engine

Abstract

This work expands the knowledge base concerning the formation of oxides of nitrogen (NO x) in the precombustion chamber (PCC) of a four-stroke lean burn (4SLB) industrial gas engine. Two analysis methods were used to characterize specific exhaust constituent concentrations formed in the PCC. The first method extracted gas from the PCC and the overall engine exhaust to be analysed by the industry standard five gas rack (THC, NO x, O 2, CO 2, and CO) and a Fourier transform infrared spectrometer (FTIR) to quantify formaldehyde (CH2O), nitric oxide (NO), and nitrogen dioxide (NO2) concentrations. This paper focuses only on NO x. The engine was operated at the manufacturer's recommended conditions and at the engine's lean limit. A PCC air-fuel ratio (A/F) map was performed at each engine operating condition by varying the fuel supply pressure to the PCC. An analytical model was developed to estimate the mass flow between the PCC and main cylinder, and mass flow out of the PCC through a sample extraction apparatus. The model was applied at specific instances during the engine cycle to clarify raw emissions data obtained directly from a cylinde's PCC. The model was developed to determine the origin of the mass sampled from the PCC which, in turn, was used to correct the measured pollutant concentrations. The corrected concentrations allowed for a comparison between NO x, emissions formed in the PCC and the overall engine exhaust on a mass specific basis. PCC-formed NO x, were found to constitute ε10 per cent while operating at the manufacture's recommended conditions and upwards of ε75 per cent when at the lean limit. The second test method utilized the high-speed chemiluminescence capabilities of a Cambustion fNOX400 analyser to measure NO concentration in gas extracted from the PCC on a half crank angle basis. The intra-cycle NO data were recorded simultaneously with pressure traces from the PCC and main cylinder by a Hi-Techniques combustion analysis system. The high-speed data acquisition system provided qualitative information on both intra-cycle NO concentrations and cycle-to-cycle variations.