Injection Strategies for Heavy Duty DI Diesel Engines

Sammanfattning: Diesel engines enjoy widespread popularity in transportation and industrial systems. The reasons for this popularity are their simplicity, relatively low capital costs, durability and high fuel efficiency. However they have several drawbacks, notably high levels of noise and exhaust emissions, especially emissions of nitrogen oxides (NO_x) and soot particles. Due to strict emissions legislation, diesel engine research is oriented mainly towards the reduction of NO_x and soot emissions, while keeping or lowering the levels of noise and fuel consumption.

The scope of this PhD study was to investigate the effects of different injection strategies on the combustion and exhaust emissions formation of a heavy duty DI diesel engine: the main goal being to comply with emissions standards that will apply from 2005/2008, while maintaining or even improving fuel consumption, based on the use of advanced technologies. The study had both numerical and experimental components, but most emphasis was placed on the experimental investigation. The numerical investigation was carried out using the KIVA3V code, including the partially stirred reactor model to treat turbulence/chemistry coupling and a reduced, but still detailed, chemistry mechanism. The effects of multiple injections were investigated numerically for a constant volume combustion chamber. Besides 'conventional' measurements the experimental investigations included two-colour pyrometric observations and measurements of locally crank angle resolved piston wall temperatures. Features examined included the effects of multiple injections, injection duration, injection pressure, number of orifices and Needle Opening Pressure (NOP) on combustion, emissions formation, and fuel consumption, and for some of the injection parameters the local crank angle resolved piston wall temperature. The experiments were carried out in a single cylinder version of the Volvo D12C production engine. It was found that the combination of Exhaust Gas Recirculation (EGR) with high injection pressure would be the most appropriate combination to meet upcoming emissions restrictions.