Tham khảo tài liệu 'internal combustion engines fundamentals episode 2 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 610 INTERNAL COMBUSTION ENGINE FUNDAMENTALS FIGURE 11-28 Sealed-ring orifice ring design Correlation between exhaust hydrocarbon emissions and oil consumption rate. Production piston rings and sealed ring-orifice ring designs. SI engine at 1600 rev min imep 422 kPa equivalence ratio rc intake pressure 54 kPa MBT spark Study of this problem the one-dimensional cyclic absorption and desorption of a dilute amount of gas in a thin constant thickness isothermal liquid layer where diffusion effects are important has been carried out. It suggests that oil layers on the cylinder wall could be a significant contributor to HC emission Correlations between engine oil consumption and exhaust HC emissions provide a perspective on the relative importance of oil absorption desorption and crevice mechanisms. Wentworth measured oil consumption and HC emissions in a spark-ignition engine for a range of piston ring Some of these designs were of the sealed ring-orifice type which effectively eliminates all the crevices between the piston piston rings and cylinder and prevents any significant gas flow into or out of the ring region. HC emissions increase with increasing oil consumption for both production ring designs and the sealed ring-orifice designs as shown in Fig. 11-28. Extrapolation to zero oil consumption from normal consumption levels shows a reduction in exhaust HC levels but this decrease is significantly less than the difference in emission levels between the production and the sealed ring-orifice designs which effectively remove the major crevice region. The production piston used had a chamfered top land. The HC emissions for a normal piston top-land design would probably be higher. POOR COMBUSTION QUALITY. Flame extinction in the bulk gas before all of the flame front reaches the wall is a source of HC emissions under certain engine POLLUTANT FORMATION AND CONTROL 611 Operating conditions. As the cylinder pressure falls during the
