Potential of a Variable Compression Ratio gasoline SI Engine with very high Expansion Ratio and Variable Valve Actuation

0D/1D GTPOWERTM and IFP-C3DTM 3D combustion simulations show a clear potential when coupling VCR engine with simple mechanical VVA (twin VVT with intake VVL).
The simulations demonstrate the thermodynamic benefit from increasing the geometric Compression Ratio (CR>18:1) in combination with VVA compared to VVT strategies, thanks to the Atkinson / Miller Cycle and to the lower internal residual gases. 3D combustion simulations of high compression ratio combustion chamber geometries used with Early or Late Intake Valve Closing strategies are carried out with IFP-C3DTM. They show an indicated efficiency increase up to 10% between compression ratio 10:1 and 18:1 at low loads (BMEP<8bar).
Single cylinder engine tests have been performed with specific combustion chambers up to CR 23:1 and have confirmed the simulation results.
Finally, simulations and tests show thermodynamic benefits of the association of VCR and VVA, improving fuel consumption on driving cycles between 8 and 11% compared to a 10.5:1 fixed compression ratio engine equipped with 2 VVT. Furthermore, the fuel consumption benefit is robust through driving cycles and downsizing level. VCR-VVA engines are therefore strong competitors to engines equipped with external EGR or using lean burn strategies.