CFD gas-dynamic noise prediction of a VVA engine intake system

Modern VVA systems offer new potentialities in improving fuel consumption for spark-ignition engines at low and medium load, meanwhile they grant a higher volumetric efficiency and performance at high load. Recently introduced systems enhance this concept through the possibility of modifying the intake valve opening, closing and lift, leading to the development of almost 'throttle-less' engines. However, at low loads, the absence of throttling, while improving the fuel consumption, also produces an increased gas-dynamic noise at the intake mouth. Wave propagation inside the intake system is in fact no longer absorbed by the throttle valve and directly impact the radiated noise. In the paper, 1D and 3D simulations of the gas-dynamic noise radiated by a production VVA engine are performed at full load and in two part-load conditions. Both models are firstly validated at full load, through comparisons with experimental data. Different settings of the VVA device at part-load are moreover considered to quantify the trade-off existing between fuel consumption and radiated noise reduction. The analyses put into evidence that the optimal control strategy for fuel consumption improvement does not allow a satisfactory abatement of the radiated noise, as well. Presented results show that, at low engine speed, the VVA setting realizing the lowest fuel consumption also produces an acceptable overall noise level. On the contrary, a small fuel consumption penalty must be paid at medium speed to realize a sufficiently low radiated noise. The proposed 1D-3D procedure hence constitutes a very useful tool to realize a fully-numerical pre-calibration of the engine under development.