The Potential of Highly Premixed Combustion for Pollutant Control in an Automotive Two-Stroke HSDI Diesel Engine 2012-01-1104

An innovative alternative to overcome the load limits of the early injection highly premixed combustion concept consists of taking advantage of the intrinsic characteristics of two-stroke engines, since they can attain the full load torque of a four-stroke engine as the addition of two medium load cycles, where the implementation of this combustion concept could be promising. In this frame, the main objective of this investigation focuses on evaluating the potential of the early injection HPC concept using a conventional diesel fuel combined with a two-stroke poppet valves engine architecture for pollutant control, while keeping a competitive engine efficiency. On a first stage, the HPC concept was implemented at low engine load, where the concept is expected to provide the best results, by advancing the start of injection towards the compression stroke and it was confirmed how it is possible to reduce NO_X and soot emissions, but increasing HC and CO emissions. Additionally, even operating at low engine loads, combustion starts too early during the compression stroke, advancing the combustion phasing and worsening the engine efficiency. In a second stage, research was focused on analyzing how to improve HPC performance by means of affecting in-cylinder gas conditions, mainly reducing gas temperature during the compression stroke by reducing the effective compression ratio, reducing IGR level by increasing the valve overlap and decreasing the reactivity of the fuel/air mixture by introducing external EGR. However, the utility of these strategies for controlling the onset of combustion in two-stroke engines has been proven to be limited and combustion is still phased too early even operating with the best settings, compromising the application of the early injection highly premixed combustion concept with conventional diesel fuel in two-stroke engines.