Under contract to the Petroleum Technology Alliance of Canada (PTAC), Clearstone Engineering Ltd. conducted a study of natural gas fuelled internal combustion engines to better understand the relationship between NOx and GHG emissions and fuel consumption. The study included a literature review and field studies of Waukesha VHP GSI engines operating in the upstream oil and gas industry.
Five Waukesha L7042GSI engines modified with the installation of REMVue air to fuel ratio control systems were tested to characterize fuel consumption and emissions during a series of tests at different Lambda values. Overall load values tested ranged from 750 bhp to 1366 bhp. The nominal rated power output of current L7042GSI engines is 1480 bhp at 1200 rpm. However, previous versions were rated at levels of 1100 bhp at 1000 rpm. The engines tested included those rated at both 1100 and 1400 bhp. All engines were tested at condition that attempted to achieve NOx emission levels of 2.0 g/bhp-h (2.7 g/kWh) and all were tested in the lean burn region of operation compatible with the application of REMVue AFR control technology. Lambda values were in the range of 1.22 to 1.59. One engine appeared to be turbo limited and could not achieve NOx levels lower than about 4.0 g/bhp-h (5.4 g/kWh).
Based on the tests completed the following general conclusions are made:
- Engine operation over the Lambda ranges tested resulted in no shut downs for the reported test conditions. However, most test conditions were maintained for a few minutes and no conclusions should be drawn with respect to long term operation at any condition.
- Engine emission performance, and specifically the relationship between NOx and CO2e, has been demonstrated and, in general, AFR control technology in the lean burn region has the potential to reduce NOx emissions to levels at or below 2 g/bhp-h (2.7 g/kWh). However, application of this technology does not guarantee that a specific engine can achieve such a criterion.
- Performance of any engine is engine specific based on physical setup, maintenance and other site specific conditions not studied and exact performance levels cannot be determined a priori.
- In general, all engines performed better than the average Industry Post-REMVue reference point and both above and below the OEM (Standard Economy) Waukesha BSFC reference point. These reference points are defined in Section 3.1 where it is noted that the PostREMVue point is based on data contained in the Literature Review and the Waukesha points are from published company data sheets.
- All NOx levels achieved were less than the OEM (Standard Economy) and OEM (3-Way Catalytic Converter) reference points.