Increased Internal Combustion Engine Efficiency with Optimized Valve Timings in Extended Stroke Operation

Andyn Omanovic,Norbert Zsiga,Christopher Onder,Patrik Soltic

doi:10.3390/en14102750

Andyn Omanovic, Norbert Zsiga + Show 2 more

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https://doi.org/10.3390/en14102750

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Abstract

Spark-ignited internal combustion engines are known to exhibit a decreased brake efficiency in part-load operation. Similarly to cylinder deactivation, the x-stroke operation presented in this paper is an adjustable form of skip-cycle operation. It is an effective measure to increase the efficiency of an internal combustion engine, which has to be equipped with a variable valve train to enable this feature. This paper presents an optimization procedure for the exhaust valve timings applicable to any valid stroke operation number greater than four. In the first part, the gas spring operation, during which all gas exchange valves are closed, is explained, as well as how it affects the indicated efficiency and the blow-by mass flow. In the second part, a simulation model with variable valve timings, parameterized with measurement data obtained on the engine test, is used to find the optimal valve timings. We show that in 12-stroke operation and with a cylinder load of 5 Nm, an indicated efficiency of 34.3% is achieved. Preloading the gas spring with residual gas prevents oil suction and thus helps to reduce hydrocarbon emissions. Measurements of load variations in 4-, 8-, and 12-stroke operations show that by applying an x-stroke operation, the indicated efficiency remains high and the center of combustion remains optimal in the range of significantly lower torque outputs.

Highlights

The automotive industry is under high political pressure to decrease its fleet averageCO2 emissions
The top subplot shows the optimal EVO2 valve timing in ◦ crank angle (CA) bGTDC, the middle subplot shows the resulting indicated efficiency in %, and the bottom subplot shows the blow-by mass flow integrated over the range of the additional strokes, that is, from 540 ◦ CA to 2160 ◦ CA
We optimized the valve timings of a combustion strategy called the x-stroke, which is based on skip-cycle or skip-fire strategies and reduces the frequency of combustion events in order to increase the part-load efficiency of an internal combustion engine

Summary

Introduction

The automotive industry is under high political pressure to decrease its fleet averageCO2 emissions. The automotive industry is under high political pressure to decrease its fleet average. Effective as of the year 2020, the emission limit for new passenger cars is set by the European parliament to 95 g CO2 /km, which corresponds to a gasoline consumption of 4.06 L/100 km. If the limit, averaged over the manufacturer’s complete fleet, is exceeded, sanctions must be paid. Similar measures are applied to light- and heavy-duty commercial vehicles. In the future, these restrictions are tightened even further in order to achieve CO2 emission neutrality by 2050 [1,2,3,4]. The limitations currently in effect require novel solutions, since a modern passenger vehicle with a conventional internal combustion engine drive train is not capable of meeting the requirements [6]

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