Browse Publications Technical Papers 2016-01-0681
2016-04-05

VCR-VVA-High Expansion Ratio, a Very Effective Way to Miller-Atkinson Cycle 2016-01-0681

Increasing the efficiency of internal combustion engines is mandatory to meet ever more stringent regulations. The implementation of very high compression ratio (> 15:1) is the key to take full advantage of the association of Variable Compression Ratio (VCR) and Variable Valve Actuation (VVA) in the implementation of Miller-Atkinson cycle, leading to higher thermodynamic efficiency and thus better fuel consumption benefits.
VVA systems allow differentiating geometric compression ratio and effective compression ratio. They theoretically permit to maximize expansion ratio (i.e. geometric compression ratio) while keeping an effective compression ratio in accordance with the constraints of the knocking limits, but with a limitation on the reachable maximum Brake Mean Effective Pressure (BMEP) at low compression ratio and the associated downsizing.
In order to optimize the genuine efficiency on real driving situation, the continuous adaptation of the geometric compression ratio of an engine in a large range [8:1; 18:1] is mandatory. The requirements of the VCR technology are firstly to ensure that the optimum Compression Ratio is set within only a few engine cycles for each operating point; and secondly, the technology must also guarantee a very precise altitude of the piston at Top Dead Center at very high compression ratio to operate safely.
A specific methodology is developed to determine the optimal compression ratio for each operating point when using VCR and VVA. It combines 0D simulations and Indicated Specific Fuel Consumption (ISFC) measurements on a single cylinder engine equipped with a high compression ratio combustion chamber. The resulting brake specific fuel consumption maps are used as input data in simulations to evaluate the impact of such a geometric compression ratio range, coupled with the use of Miller/Atkinson cycle, on fuel consumption on standard cycles for given vehicles.

SAE MOBILUS

Subscribers can view annotate, and download all of SAE's content. Learn More »

Access SAE MOBILUS »

Preview Document Add to Cart
Members save up to 16% off list price.
Login to see discount.
Special Offer: Download multiple Technical Papers each year? TechSelect is a cost-effective subscription option to select and download 12-100 full-text Technical Papers per year. Find more information here.
We also recommend:
TECHNICAL PAPER

Investigations of Atkinson Cycle Converted from Conventional Otto Cycle Gasoline Engine

2016-01-0680

View Details

TECHNICAL PAPER

Study on Fuel Economy Improvement by Low Pressure Water-Cooled EGR System on a Downsized Boosted Gasoline Engine

2016-01-0678

View Details

TECHNICAL PAPER

Extending the Dilution Limit of Spark Ignition Combustion via Fuel Injection during Negative Valve Overlap

2016-01-0671

View Details

X