Guidance of IMO for NOx emission is now being prepared expecting to be effective within some years objecting diesel engines of 100kW or more. Following to this first stage target figure, the value will be checked continuously, by every five years until it reaches to a certain value.
Emission of NOx from low-speed 4-stroke engine is comparatively more than high or medium speed engines. Generally, as the reduction of NOx emission adversely affects fuel consumption, it is important to pay attention to minimize increase of fuel consumption.
Approximately ten per cent reduction of NOx emission has been achieved by using fuel valve with increased number of nozzle holes aiming at realizing an equalized combustion with no partial hot spot. It is also known that injection timing retarding by raising compression ratio results in less increase of fuel consumption rather than retarding by raising up charged air pressure. It has been also confirmed that NOx emission is reduced by 20 per cent in E3 figure by retarding fuel injection timing particularly in light load condition.
In general, retarding results in emission of particulates, however, transparency of smoke was kept during all period of the test carried out on LH41L engine which excells in combustion in itself.
Table 2 shows the test result of NOx emission of LH41L.
