Effect of the Intake Valve Lift and Closing Angle on Part Load Efficiency of a Spark Ignition Engine

Michelangelo Balmelli,Laura Merotto,Norbert Zsiga,Patrik Soltic

doi:10.3390/en13071682

Michelangelo Balmelli, Laura Merotto + Show 2 more

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https://doi.org/10.3390/en13071682

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Abstract

This study provides an experimental evaluation of the effectiveness of Miller cycles with various combinations of lift and intake valve closing angle for a passenger car engine with premixed combustion in naturally aspirated operation. A fully variable electro-hydraulic valve train provided different valve lift profiles. Six load points, from 1.5 up to 5 bar brake mean effective pressure at a constant engine speed of 2000 min−1, were tested with 6 different intake valve lift/intake valve closing angle combinations. The intake valve closing angle was always set before bottom dead center to achieve the desired load with unthrottled operations. Experimental comparison with throttled operation outlines an indicated efficiency increase of up to 10% using high intake lift with early valve closing angle. Furthermore, this analysis outlines the influences that early intake valve closing angle has on fuel energy disposition. Longer combustion duration occurs using early intake valve closing angle because of turbulence dissipation effects, leading to slight reductions in the heat-to-work efficiency. However, overall pressure and temperature levels decrease and consequently heat losses and losses due to incomplete combustion decrease as well. Overall, we found that combustion deterioration is compensated/mitigated by the reduction of the heat losses so that reductions of pumping losses using early intake valve closing can be fully exploited to increase the engine’s efficiency.

Highlights

This work outlines an experimental investigation of unthrottled Miller cycles using a self-developed electro hydraulic valve train [1,2]
This was to gain a basic insight about the different influences of early intake valve closing angle and valve lift on overall efficiency, pumping losses, and combustion deterioration
This paper presents the experimental results achieved by applying early intake valve closing (IVC) (Miller cycle) to a four-cylinder engine operated with natural gas and fitted with a fully variable electro-hydraulic valve train

Summary

Introduction

This work outlines an experimental investigation of unthrottled Miller cycles using a self-developed electro hydraulic valve train [1,2]. In conventional stoichiometrically operated spark ignition engines, which control the amount of aspirated gas by throttling the intake airflow, pumping losses make the engine efficiency deteriorate significantly, in particular at low loads. This leads to high fuel consumption during typical operation of non-hybrid powertrains [3]. Controlling the amount of fresh gas by adjusting the intake valve closing (IVC) angle promises to reduce or eliminate pumping losses. The resulting cycles are usually called Miller and Atkinson, respectively. Late IVC (Atkinson) as a general strategy for load control is problematic, because late intake closing interferes at low load with the ignition angle. Early IVC (Miller) was used throughout the work presented here

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