Crevice Volume Effect on Spark Ignition Engine Efficiency 2014-01-2602

The effects of piston top-land crevice size on the indicated net fuel conversion efficiency are assessed in a single cylinder SI engine with 465 cc displacement and 11.2 compression ratio. The operating conditions are at 3.6 and 5.6 bar net indicated mean effective pressure (NIMEP), and at 1500 and 2000 rpm speeds. The cold crevice volume is varied from 524 mm³ to 1331 mm³ by changing the top land height from 3 to 7 mm, and by changing the top-land clearance from 0.247 to 0.586 mm. For a 100 mm³ increase in the top land crevice volume (estimated hot value), the indicated net fuel conversion efficiency decreases by 0.1 percentage point at 1500 rpm, and by 0.13 percentage points at 2000 rpm. The results are not sensitive to the two NIMEP values tested. These values are consistent with a simple crevice filling and discharge/oxidation model.