Experimental study of NOx reduction on a medium speed heavy duty diesel engine by the application of EGR (exhaust gas recirculation) and Miller timing

Emission legislation that applies to engines used in shipping, rail and land power generation becomes increasingly strict. E.g. IMO Tier III applicable to sea-going vessels limits the NOx emission by 75% compared to IMO Tier II. Attaining these without sacrificing fuel consumption is a big challenge. This paper reports on engine internal measures that can provide a viable alternative to expensive (running costs) and bulky after-treatment. EGR (exhaust gas recirculation) and early intake valve closing as NOx reduction techniques are mature technologies on automotive applications but on medium speed diesel engine as investigated here, these are still not straightforward to implement. Two camshaft configurations are considered under EGR operation. In this research, a new approach for determining the EGR rate is developed. The effects of various EGR rates on fuel consumption and engine-out emissions are investigated, while in-cylinder pressure measurements and calculated AHRR (apparent heat release rates) provide more insight into the physical effects of EGR on the combustion.