Marine Engineering

These are measures designed to remove NOx from the exhaust gas by downstream cleaning technique. The most common secondary measures are – SCR ( Selective catalytic reduction) :- In this system the exhaust gas is mixed with ammonia before passing through a layer of special catalyst at a temperature between 300 deg Celsius to 450 deg Celsius. The NOx is reduced to gaseous and harmless by-products of water and nitrogen. SNCR( Selective non-catalytic reduction) :- In case of SNCR, the reaction between ammonia and NOx takes place in a gaseous phase in a temperature window of between 800 and 900 deg Celsius. The most effective method of NOx reduction is a secondary measure.  The advantages are:- Secondary measures reduce NOx in case of SCR of up to 80- 95% and in case of SNCR 30-50%. Whereas primary measures average Nox reduction is up to 25- 35%. Possible side effects of primary measures are lower overall energy efficiency, increased carbon mono-oxide, and soot formation and hydrocarbon...

These are measures aimed at reducing the amount of NOx formed during combustion by optimizing engine parameters with respect to emission. Some of the methods are listed below – A. Water addition:- Direct water injection:- Greater heat capacity is utilized to reduce high peak temperatures as the water evaporates immediately upon injection. Rapid evaporation of injected water also helps to create a homogeneous fuel-air mixture. Emulsified fuel or fuel-water emulsion:- It is favored by some manufacturer claiming a clear reduction in NOx emission at low cost with no significant design changes. B. Altered fuel injection:- Delayed fuel injection:- Retarded fuel injection timing retards the  combustion process. Nitrogen oxide formation occurs later and with lower concentration. Common rail control:- It has proven to be a very effective way in combating  NOx reduction techniques. NOx optimized fuel spray pattern:- Different fuel nozzle types and model  injection also has an influ...

There are two methods to reduce NOx emissions; Primary and secondary measures.  Primary measure aim at reducing the amount of NOx formed during combustion by optimizing engine parameters with respect to emissions. As read in previous article , the  main factors influencing NOx formation  are the concentrations of oxygen and  nitrogen and the local temperature in  the combustion process. Therefore,the  primary measures focus on lowering the  concentrations, peak temperature and the  amount of time in which the combustion  gases remain at high temperatures. Miller cycle is employed in 4-stroke  engines. It uses higher than normal  pressure turbocharger. The inlet valve is  closed before the piston reaches bottom  dead center on the intake stroke. The  charge air then expands inside the engine  cylinder resulting in reduced temperature. On the other hand, secondary measures remove NOx from the exhaust ga...