Numerical assessment of the CO2 reduction potential of Variable Valve Actuation on a Light Duty Diesel engine

The increasingly demanding targets in terms of CO2 reduction lead to the adoption of engine technologies left so far for innovation. In diesel engines, some of the primary interests in adopting an advanced air management system, as Variable Valve Actuation (VVA), are related to Miller cycle enabling, and valve timing optimization. In this context, a numerical study was carried out in order to evaluate the impact of VVA on passenger car 4-cylinder diesel engine, 1.6 liters. The engine model, developed in GT-SUITE, features a predictive combustion model (DIPulse) and it is coupled with a fully predictive fuel injector model for the simulation of complex injection patterns. 3 different VVA techniques were evaluated, all targeting CO2 reduction: Late Exhaust Valve Opening (LEVO), Exhaust Phasing, and Late Inlet Valve Closure (LIVC) for enabling Miller cycle. In steady state conditions, only LIVC showed significant reduction in terms of fuel consumption (up to 5% at low engine loads) without exceeding the baseline Brake Specific engine-out NOx emissions. Afterwards, the LIVC impact was evaluated under transient conditions over the different driving cycles, such as the Worldwide harmonized Light vehicles Test Cycle (WLTC).