The HOTFIRE Homogeneous GDI and Fully Variable Valve Train Project - An Initial Report

While new types of spray-guided gasoline direct injection (GDI) combustion systems are finally set to yield the level of fuel consumption improvement which was originally promised for the so-called ‘first generation’ wall- and air-guided types of GDI, injectors for spray-guided combustion systems are not yet in production to help justify the added complication and cost of the NOx trap necessary with a stratified combustion concept. Conversely, hardware suitable for homogeneous combustion systems is available now and this approach offers the advantage that simple three-way catalysis only needs to be used for exhaust gas aftertreatment. This in turn means that homogeneous GDI is a technology applicable to a world-wide market, because NOx traps are susceptible to poisoning by sulphur, such as is to be found in high concentrations in US gasolines.

Advanced mechanically-variable valve trains are in production now, which considerably reduce pumping losses in the 4-stroke engine over the conventional ‘variable density’ type of throttling. Fully variable valve trains are being developed to production, too. These technologies allow throttling loss to be addressed directly rather than by the more circuitous route of stratified charge combustion. While homogeneous combustion systems with load control by valve event may not offer the ultimate thermodynamic benefits of stratified charge, the fuel consumption improvement possibilities are still considerable, relative to a state-of-the-art port fuel injection engine.

The present work discusses the start of the HOTFIRE consortium project which is a three-year programme to investigate the strong interactions and synergies between homogeneous GDI and fully variable valve train systems. Initial results from the consortium's high-speed optical access engine, fitted with a research fully variable valve train system, are presented. Work responsibilities within the project are discussed together with the potential of the assembled test equipment to look at the interaction between variable valve trains and spray-guided GDI systems in the future.