Improving Fuel Economy in a Turbocharged DISI Engine Already Employing Integrated Exhaust Manifold Technology and Variable Valve Timing

Many new technologies are being developed to improve the fuel consumption of gasoline engines, including the combination of direct fuel injection with turbocharging in a so-called ‘downsizing’ approach. In such spark ignition engines operating on the Otto cycle, downsizing targets a shift in the operating map such that the engine is dethrottled to a greater extent during normal operation, thus reducing pumping losses and improving fuel consumption. However, even with direct injection, the need for turbine protection fuelling at high load in turbocharged engines - which is important for customer usage on faster European highways such as German Autobahns - brings a fuel consumption penalty over a naturally-aspirated engine in this mode of operation.

In addition to the continual increase in permissible turbine inlet temperature that metallurgical development has provided, both cooled exhaust manifolds and the use of diluents (principally cooled EGR) have been shown to reduce the need for high-load component protection fuelling. This paper reports test work performed using a state-of-the-art 1.5 litre close-spaced direct injection turbocharged engine, fitted as standard with an exhaust manifold integrated into the cylinder head, aimed at exploring any synergies from combining this base engine technology with increased turbine inlet temperature or cooled EGR.