Investigation of Early and Late Intake Valve Closure Strategies for Load Control in a Spark Ignition Ethanol Engine

摘要

The more strict CO_2 emission legislation for internal combustion engines demands higher spark ignition (SI)engine efficiencies. The use of renewable fuels, such as bioethanol, may play a vital role to reduce not only CO_2 emissions but also petroleum dependency. An option to increase 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 intake valve closure reduces pumping losses (the main cause of the low part load efficiency in SI engines) but 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 paper investigates the effects of early and late intake valve closure strategies in the gas exchange process, combustion, emissions and engine efficiency at unthrottled stoichiometric operation. A four-valve four-stroke single cylinder camless engine running with port fuel injection of anhydrous ethanol was employed. Early and late intake valve closure (EIVC and LIVC) 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. The consequences 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 for EIVC strategy. Comparatively, the EIVC strategy presented better overall performance than the LIVC. Both unthrottled strategies provided higher engine efficiency than the conventional throttled SI strategy.