SOLUTIONS FOR MEETING LOW EMISSION REQUIREMENTS IN LARGE BORE NATURAL GAS ENGINES
Across the entire Natural Gas engine industry, operators and OEMs are faced with increased expenses and the deterioration of engine performance as they struggle in meeting the mandated lower emission levels. In the sector of large bore engines, greater than 250mm, the field is populated by two combustion strategies aiming at meeting lower emissions. A significant percentage of large bore, low speed engines, use two spark plugs per cylinder to enhance the combustion rate. The remaining population of engines uses precombustion chambers with a dedicated fuel feed and controls to generate a rich air-fuel mixture in the vicinity of a conventional spark plug. Using a precombustion chamber adds complexity, cost and reduces reliability. Although lower emissions are achieved with fuel fed prechambers, the engine stability with leaner mixtures still remains the limiting factor compromising the performance of the engine. This paper describes a cost effective solution for each of the combustion strategies. These solutions aim at extending the lean limit of operation, hence, meeting the lower emission requirements with improved combustion stability. In the case of large bore, low speed engines currently using conventional spark plugs, it is possible to avoid the costs associated with the conversions to fuel-fed precombustion chambers by simply replacing the conventional spark plugs with specially designed passive prechamber spark plugs. These highly effective designs are obtained with the latest technology in computational flow dynamic (CFD) that uses the CONVERGE detail chemistry CFD software. Results from engine testing indicate that specially designed passive prechamber spark plugs achieve stable engine operation at NOx emission levels below 500mg/Nm3 (1.0g/bhp-hr). n the case of engines which already have a fuel-fed precombustion chamber, lower emissions can be achieved with the use of a passive prechamber spark plug in place of the conventional spark plug to form a two stage precombustion chamber operating with significantly leaner mixtures. The flame jets emerging from the passive prechamber spark plug compensates for the slower flame propagation rates associated with lean prechamber combustion. The optimum design of the two-stage precombustion chamber, the amount of fuel required, the fuel injection timing and the spark discharge characteristics are also determined with the latest technology in computational flow dynamic (CFD) that uses the CONVERGE detail chemistry CFD software. An electronic fuel control valve provides the amount of fuel required at the correct timing. Furthermore, an ignition system with a tunable high energy spark discharge waveform achieves the desired combustion stability while maintaining a long plug life. Engine test results from this system indicate stable engine operations at NOx emissions levels below 250mg/Nm3 (0.5g/bhp-hr). The solutions demonstrated in this paper provide enough evidence to warrant consideration by OEMs for immediate use in large bore gas engines.
Emmanuella Sotiropoulou David Lepley Luigi Tozzi
Prometheus Applied Technologies,LLC,USA Altronic,LLC,USA
国际会议
上海
英文
1-12
2013-05-13（万方平台首次上网日期，不代表论文的发表时间）