Advanced hybrid electronic unit injector with accumulator for enhanced multiple injection and ultra high injection pressure capability

In order to meet new worldwide emission regulations for heavy-duty diesel engines and to provide high specific power output without fuel consumption penalties there is a requirement for the fuel injection system to have a flexible choice of injection characteristics. Such a fuel injection system has to provide multiple injections, modulated injection pressures and rates for every injection, and possibly variable spray cone angle to accommodate early injection without wall wetting whilst maintaining conventional injection for rated power.

The aim of this paper is to present the advanced hybrid electronic unit injector system (EUI). This system incorporates an accumulator rail, which enables high pressure multiple injection events at different injection pressures for a very wide range of injection timings that would not normally be achievable using a conventional EUI system and single lobe EUI camshaft. It also has the ability to do boot shape injections starting from a constant rail pressure which merges into a rapidly rising pressure mid injection.

The experimental work was performed on a single cylinder heavy-duty research engine at key operating modes. The results show that engine emissions can be reduced whilst specific fuel consumption is improved. The results obtained show potentials in controlling injection rate, shape and timing compared to a conventional EUI system.