Comparison between early and late intake valve closure events as load control strategies in a spark ignition ethanol engine

Paper #:
  • 2017-01-0643

Published:
  • 2017-03-28
Abstract:
The more strict legislation for internal combustion engines CO2 emissions demands higher engine efficiency. The use of renewable fuels, such as bioethanol, may play a vital role to reduce not only CO2 emissions but also oil dependency. An option to increase spark ignition (SI) four stroke engine efficiency is to use the so called over-expanded cycle concepts by variation of the valve events. The use of an early or late inlet valve closure reduces pumping losses (the main cause of the part load low efficiency in SI engines) and decreases the effective compression ratio. The higher expansion to compression ratio leads to better use of the produced work and also increases engine efficiency. This study presents the engine combustion, performance and emissions of the unthrottled stoichiometric operation of a four valves four stroke single cylinder camless engine. Early and late inlet valve closure strategies with a fixed maximum valve lift were compared to a conventional throttled SI valve event strategy for loads from 2.0 to 9.0 bar IMEP at 1500 rpm. Port fuel and direct injection strategies were compared in order to find the best trend between emissions and indicated efficiency. The challenges and benefits to implement the unthrottled operation with each strategy were discussed. To better understand the effect of the maximum valve lift at a specific load, the valve lift was varied from 1.5 to 5.0 mm and its effects were discussed. Comparatively, the early inlet valve closure strategy presented better overall performance than the late inlet valve closure strategy. Both unthrottled strategies provided higher engine efficiency than the conventional SI valve event strategy. PFI provided overall better charge mixture preparation process which led to better combustion efficiency.
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