Multiple injection and rate shaping Part 1: Emissions reduction in passenger car Diesel engines 2009-24-0004
In modern passenger car diesel engines, multiple injection, MI, and rate shaping are measures, which in conjunction with others help to achieve the emissions legislation EU6 and US Tier2 Bin5. However, where hitherto mainly pollutant emissions where considered, CO2 output - i.e. fuel consumption - becomes increasingly important. Also, off cycle emissions may have to be regarded in the future. Additionally engine noise and drivability need consideration.
The complexity and effect of an applied injection strategy is defined by the overall engine concept including the after treatment system, and also by the vehicle inertia. Additionally a modern fuel injection system not only has to allow for the necessary injection strategies but at the same time needs to offer robust performance over life time.
Although a complex injection system may entail a penalty in cost, this has to be regarded in the context of the complete engine system including a possibly needed exhaust gas after-treatment, since a more expensive injection system can contribute to an overall reduction in cost. A well applied and stable injection system may allow for a simple and cheap after treatment system to be used, optimised for low engine exhaust back pressure.
In the present work, the improvements in mixture formation and combustion through multiple injection strategies, MI, and injection rate shaping were investigated. In particular, combination of ramp injection with pilot and post injections were examined. This was done, using a 500 cm3 single cylinder research engine and the Continental directly actuated piezo injector, which allows for the stable application of partial needle lifts for injection rate shaping.
The current report provides evidence that appropriate injection patterns in combination with suitable boost andinjection pressures serve to achieve EU6 emissions engineering targets at the investigated operating points.
The physio-chemical effects of MI and rate shaping were also analysed by means of 3D combustion simulation, in order to improve the understanding and, hence, facilitate the appropriate application of the injection strategies. A detailed treatise on the computational investigation is provided in Part 2 of this paper (SAE 20009-24-0012).