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Reported in the current paper is a study into the cycle efficiency effects of utilising a complex valvetrain mechanism in order to generate variable in-cylinder charge motion and therefore alter the dilution tolerance of a Direct Injection Spark Ignition (DISI) engine. A Jaguar Land Rover Single Cylinder Research Engine (SCRE) was operated at a number of engine speeds and loads with the dilution fraction varied accordingly (excess air (lean), external Exhaust Gas Residuals (EGR) or some combination of both). For each engine speed, load and dilution fraction, the engine was operated with either both intake valves fully open - Dual Valve Actuation (DVA) - or one valve completely closed - Single Valve Actuation (SVA) mode. The engine was operated in DVA and SVA modes with EGR fractions up to 20% with the excess air dilution (Lambda) increased (to approximately 1.8) until combustion stability was duly compromised.

Diesel engine designers often use swirl flaps to increase air motion in cylinder at low engine speeds, where lower piston velocities reduce natural in-cylinder swirl. Such in-cylinder motion reduces smoke and CO emissions by improved fuel-air mixing. However, swirl flaps, acting like a throttle on a gasoline engine, create an additional pressure drop in the inlet manifold and thereby increase pumping work and fuel consumption. In addition, by increasing the fuel-air mixing in cylinder the combustion duration is shortened and the combustion temperature is increased; this has the effect of increasing NOx emissions. Typically, EGR rates are correspondingly increased to mitigate this effect. Late inlet valve closure, which reduces an engine’s effective compression ratio, has been shown to provide an alternative method of reducing NOx emissions.

Modern diesel cars, fitted with state-of-the-art aftertreatment systems, have the capability to emit extremely low levels of pollutant species at the tailpipe. However, diesel aftertreatment systems can represent a significant cost, packaging and maintenance requirement. Reducing engine-out emissions in order to reduce the scale of the aftertreatment system is therefore a high priority research topic. Engine-out emissions from diesel engines are, to a significant degree, dependent on the detail of fuel/air interactions that occur in-cylinder, both during the injection and combustion events and also due to the induced air motion in and around the bowl prior to injection. In this paper the effect of two different piston bowl shapes are investigated.

There is an increasing recognition of injector deposit (ID) formation in fuel injection equipment as direct injection spark ignition (DISI) engine technologies advance to meet increasingly stringent emission legislation and fuel economy requirements. While it is known that the phenomena of ID in DISI engines can be influenced by changes in fuel composition, including increasing usage of aliphatic alcohols and additive chemistries to enhance fuel performance, there is however still a great deal of uncertainty regarding the physical and chemical structure of these deposits, and the mechanisms of deposit formation. In this study, a mechanical cracking sample preparation technique was developed to assess the deposits across DISI injectors fuelled with gasoline and blends of 85% ethanol (E85).