With introduction of IMO (International Maritime-Organisation) Tier III in 2016 the marine diesel engine technology faces a radical change. The IMO Tier III requires nitric oxide (NO(x)) reductions of 75 % compared to the current level (IMO Tier II). In connection with the stringent NO(x) reductions massive sulfur oxide (SO(x)) reductions will be introduced stepwise till 2015. In light of this, the potential of exhaust gas recirculation (EGR) to fulfill the IMO Tier III NO(x) limits at medium-speed marine diesel engines is systematically analyzed. The targets are defined by a NO(x) emissions level of 2 g/kWh, invisible smoke and minimum fuel consumption penalty. The analyses are carried out at a six-cylinder mediumspeed test engine with 1,000 kW output @ 1000 rpm. The research engine is equipped with a cooled EGR system, a common-rail injection system and a programmable engine control unit. The CR injectors are solenoid-operated and allow multiple injections. Systematic variations of EGR rate, injection pressure and injection timing were carried out and the results regarding combustion process, NO(x) and soot emissions as well as fuel consumption are presented. The results show, that significant EGR rates are necessary, to obtain NO(x)-reduction rates as required for IMO Tier III compliance. These high EGR rates result in unwanted and unacceptable soot emission levels even at increased injection pressures. To reduce these soot emissions, post-injection strategies were analyzed at the medium-speed test engine. Post-injection proved to be an efficient soot reduction measure in on-road diesel engine. The effect of different post-injections on the soot emissions is shown. Based on the results the soot emission reduction potential of post-injections at marine medium-speed diesel engines is outlined and the requirements for a successful implementation of post-injection strategies are discussed. The application of post-injections requires detailed information on the dynamic behavior of the common-rail system and especially on the CR-injectors applied. Due to this, the dynamics of the CR injectors in case of post-injections were established at an injection rate analyzer and the findings are discussed. The functionality of the CR injectors at the test engine is monitored by measurements of the current feed signal and the injection pressure at the injector inlet. Finally, the preconditions for a successful application of EGR at medium-speed marine diesel engines are summarized. The use of EGR not only challenges the injection (rail pressure, postinjections), charging and the cooling system (EGR, charge air) but also the engine control system.
Combination of post-injection and cooled EGR at a medium-speed diesel engine to comply with IMO Tier III emission limits
2013
9 Seiten, 21 Bilder, 7 Quellen
Conference paper
English
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