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Achieving the Max - Potential from a Variable Compression Ratio and Early Intake Valve Closure Strategy by Combination with a Long Stroke Engine Layout
ISSN: 0148-7191, e-ISSN: 2688-3627
Published September 04, 2017 by SAE International in United States
This content contains downloadable datasetsAnnotation ability available
The combination of geometrically variable compression (VCR) and early intake valve closure (EIVC) proved to offer high potential for increasing efficiency of gasoline engines. While early intake valve closure reduces pumping losses, it is detrimental to combustion quality and residual gas tolerance due to a loss of temperature and turbulence. Large geometric compression ratio at part load compensates for the negative temperature effect of EIVC with further improving efficiency. By optimizing the stroke/bore ratio, the reduction in valve cross section at part load can result in greater charge motion and therefore in turbulence. Turbocharging means the basis to enable an increase in stroke/bore ratio, called β in the following, because the drawbacks at full load resulting from smaller valves can be only compensated by additional boosting pressure level.
In this publication, the potential of an optimized stroke/bore ratio in combination with EIVC and VCR at part and full load is effectively assessed with a combination of 1D/QD and 3D-CFD simulation. In order to obtain reliable results, additional model approaches, such as turbulence, combustion and knock models were applied in 1D/QD simulation.
Increasing the stroke/bore (β) ratio from 1.07 to 1.4 is capable of increasing the turbulent kinetic energy by 30 % at the operating point n = 2000 rpm/BMEP = 2 bar with EIVC. Together with a compression ratio of 16.5, this results in 7 % higher residual gas tolerance which significantly reduces pumping losses. The reduced wall heat losses on increasing the stroke/bore ratio leading to an even further increased optimum compression ratio by 1.5 units to 18. By combining EIVC, high compression and optimum stroke/bore ratio of 1.4, it was possible to determine fuel consumption of BSFC = 317 g/kWh at 2000 rpm/2 bar (FMEP = 0.65 bar). This means a reduction in fuel consumption of about 9 % compared to the basis with stroke/bore ratio 1.07, EIVC and compression ratio 10.
By taking into consideration new driving cycles and new powertrain concepts, the low-load range is becoming increasingly less relevant or significant. Therefore, the useful maximum compression ratio for part load decreases. A reasonable spread of geometric compression ratio for part and full load would appear to be just 4 units in the range of 12 - 16.
CitationSens, M., Guenther, M., Hunger, M., Mueller, J. et al., "Achieving the Max - Potential from a Variable Compression Ratio and Early Intake Valve Closure Strategy by Combination with a Long Stroke Engine Layout," SAE Technical Paper 2017-24-0155, 2017, https://doi.org/10.4271/2017-24-0155.
Data Sets - Support Documents
|Unnamed Dataset 1|
- Potential of the Variable Compression Ratio on a Fully “Millered” Gasoline Engine MTZ 04/2016
- Morel , T. and Keribar , R. A Model for Predicting Spatially and Time Resolved Convective Heat Transfer in Bowl-in-Piston Combustion Chambers SAE Technical Paper 850204 1985 10.4271/850204
- Dingel , O. , Seidel , T. , and Steuker , H. In-cylinder Flow Field Measurement with Doppler Global Velocimetry in Combination with Droplet Distribution Visualization by Mie Scattering SAE Technical Paper 2009-01-0652 2009 10.4271/2009-01-0652
- Shelby , M. , Leone , T. , Byrd , K. , and Wong , F. Fuel Economy Potential of Variable Compression Ratio for Light Duty Vehicles SAE Int. J. Engines 10 3 2017 10.4271/2017-01-0639
- Wolfgang , S. , Sorger , H. , Loesch , S. , Unzeitig , W. et al. The 2-Step VCR Conrod System - Modular System for High Efficiency and Reduced CO2 SAE Technical Paper 2017-01-0634 2017 10.4271/2017-01-0634
- Constensou , C. and Collee , V. VCR-VVA-High Expansion Ratio, a Very Effective Way to Miller-Atkinson Cycle SAE Technical Paper 2016-01-0681 2016 10.4271/2016-01-0681