【作者】

Hiroshi Tajima

【摘要】

论文已在上海2013年CIMAC大会上发表，论文版权归CIMAC所有。 The IMO (International Maritime Organization) Tier lll regulations against the emissions from vessels require rigorous reduction of SOx(Sulphuric Oxides) as well as PM(Particulate Matter) and NOx(Nitrogen Oxides). From 2015, LSFO (Low Sulphur Fuel Oil) required in ECA (Emission Control Area) should decrease its sulphur content to 0.1 mass% of fuel, which is equal to one tenth of the present sulphur level required of LSFO (Low Sulphur Fuel Oil). The NOx emission rate [g/kWh] should be reduced by as much as 75% from the present tier ll level from 2016. Although various anti-NOx-pollution technologies, like an EGR (Exhaust Gas Recirculation) or a SCR (Selective Catalytic Reduction) have been ardently investigated, there exist three strong obstacles to inhibit these technologies from practical use. The first is sulphur content of the LSFO still high enough to result in metal corrosions in the EGR system by sulphuric acid and in catalyst occlusion in the SCR system by ammonium hydrogen sulphate after long term use. The second is a wider load range required for propulsion engines by the emission regulation in marine sector. It is difficult in general to adjust the exhaust clarifying devices especially at low-load operations, since the enthalpy of the exhaust gas is not sufficient to activate such devices. For example, more EGR rate is necessary in lower-load conditions to avoid severe combustion deterioration due to the lack of oxygen, but this implies more power consumption of an EGR blower in the system and the total thermal efficiency could be disastrous. The third is the additional operation cost of the NOx-reduction systems. The EGR system needs a neutralizing treatment system of the sulphuric acid scrubbed down from the EGR gas and the SCR system consumes urea or ammonia water according to the NOx concentration in the exhaust pipes. Moreover, the LSFO would be very expensive marine fuel as long as it is supplied with gas oil classification of low sulphur content, so that other low-sulphur yet inexpensive components are desirable to burn in marine engines. On the whole, a supplementary and economical anti-NOx, pollution system is definitely wanted to cover the lower-load range without fear of the cost increase in fuel consumption and device operation. From above point of view, PCCI (Premixed Charge Compression ignition), which has been studied in smaller on-road fields for long time, could be a practical remedy for the first time for the emissions from marine diesels. In this study, a new PCCI combustion system is proposed to achieve drastic NO, reduction for marine diesels. This system utilizes a set of sprays from closely aligned holes having injection directions intersecting one another so as to cause mutual interaction and merger of the sprays by overlapping injection periods and applying different injection rates. It can enhance the mixture stratification suitable for the PCCI combustion. As for the cheaper substitute of the low-Sulphur gas oil, neat LCO (Light Cycle Oil) was also firstly introduced as a potential LSFO in this study. LCO is composed from distillate components produced in a FCC (Fluid Catalytic Cracking) process in modern oil refinery plants and it has sometimes notoriety for its poor ignitability thanks to its high aromaticity. LCO was casted in a new light here by utilizing its good valorousness and its long ignition delay for the PCCI combustion. Lower-load operation also favours the PCCI concept because the abnormal combustion of the PCCI mode usually happens at higher-load conditions. The durability against the preignition of LCO was greatly enhanced by water emulsification. The potential of the strategy was examined through observation of the spray merging and combustion process in a rapid compression expansion machine. All in all, the ignition control of PCCI combustion in large engines was successfully realized for the first time.

【会议名称】

第27届CIMAC会议

【会议地点】

上海

【下载次数】

1

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