Comparison between Unthrottled, Single and Two-valve Induction Strategies Utilising Direct Gasoline Injection: Emissions, Heat-release and Fuel Consumption Analysis

Abstract

<div class="htmlview paragraph">For a spark-ignition engine, the parasitic loss suffered as a result of conventional throttling has long been recognised as a major reason for poor part-load fuel efficiency. While lean, stratified charge, operation addresses this issue, exhaust gas aftertreatment is more challenging compared with homogeneous operation and three-way catalyst after-treatment. This paper adopts a different approach: homogeneous charge direct injection (DI) operation with variable valve actuations which reduce throttling losses. In particular, low-lift and early inlet valve closing (EIVC) strategies are investigated.</div> <div class="htmlview paragraph">Results from a thermodynamic single cylinder engine are presented that quantify the effect of two low-lift camshafts and one standard high-lift camshaft operating EIVC strategies at four engine running conditions; both, two- and single-inlet valve operation were investigated. Tests were conducted for both port and DI fuelling, under stoichiometric conditions.</div> <div class="htmlview paragraph">Measurements of specific fuel consumption and exhaust emissions were carried out, while the combustion was analysed using heat release analysis. These tests were carried out in a thermodynamic single cylinder engine. In parallel, tests were conducted in a second engine having the same combustion chamber geometry but with extensive optical access through a transparent cylinder liner. The results from the thermodynamic engine were correlated with in-cylinder measurements in the optical engine of the fuel spray.</div> <div class="htmlview paragraph">The results show that there are worthwhile fuel consumption and exhaust emission benefits to be gained through de-activation of one of the two inlet valves at part-load conditions. The performance characteristics under certain load conditions were dependant on which intake valve was actuated.</div>