A new exhaust after treatment
system that is said to allow radical improvements in fuel efficiency in
diesel engines and meets strict new European regulations on NOx emissions
has been unveiled by IMI Vision. The group says its Sigma development
is set to revolutionise the Selective Catalytic Reduction (SCR) market
because it can save truck operators up to €6,000 per vehicle over
five years when compared with “wet” SCR systems.
Sigma differs radically from existing “wet” SCR technologies in that, instead of using a liquid urea solution spray to reduce NOx emissions, it injects the ammonia into the exhaust as a gas.
IMI Vision says the system will not only help manufacturers and hauliers comply with Euro 4 regulations on vehicle emissions, which come into effect from September, but have them ready for the still tighter Euro 5 regulations that become effective from October 2008.
Patrick Ward , business development manager at IMI Vision, says: “The potential benefits to truck owners could be up to €6,000 per vehicle in improved fuel consumption, less urea usage and reduced maintenance.
“Sigma allows diesel engines to be mapped more aggressively, allowing increased fuel savings of up to three per cent above traditional SCR systems, and eight per cent above non-SCR engines. In addition it’s substantially more efficient, simpler, and requires less maintenance.
“This is the next wave of SCR technology. Rather than making small improvements to existing SCR systems, we’re taking a leap forward with a technology that will have manufacturers and hauliers ready, not just for Euro 4, but Euro 5 and beyond.”
Sigma is far smaller than wet systems – in fact it can be built into the exhaust pipe, instead of alongside it – which means the system can be scaled down for almost any diesel engine.
Ward added: “We believe Sigma will become the industry norm, not just for trucks, but eventually for diesel-powered vans, cars and boats as well.”
Traditional SCR systems are “wet” in that they inject AdBlue – a water and urea solution – into the exhaust system to reduce nitrous oxide and nitrous dioxide emissions. In the exhaust stream the urea is converted into ammonia, which reacts with these NOx gasses in the catalytic converter, to produce harmless nitrogen and water vapour.
However wet systems have many drawbacks: they are bulky because the urea solution needs to be injected about a metre from the catalytic converter to atomise properly.
The urea can also turn into hard deposits that build up in the exhaust system, particularly around the injection nozzle. That means trucks using wet SCR systems have to get rid of deposits by blasting compressed air through the dosing nozzle, leaving them susceptible to hard vehicle shutdowns or low quality air supply.
In addition wet systems are also inefficient: up to 30 per cent of an SCR catalytic converter is taken up reconverting isocyanic acid (an undesirable by product of the urea decomposition process) into ammonia gas. Too much urea spray can ‘blind’ the catalytic converter, again hampering its efficiency in reducing NOx emissions.
What makes Sigma revolutionary is that, instead of spraying liquid urea into the exhaust system, it is turned into a gas using a system called controlled hydrolysis. The gas is then buffered before being released into the exhaust fumes.
Using a gas, rather than a liquid, has an enormous number of benefits for truck owners. It is far more efficient at reducing NOx emissions – about 90 per cent effective in test conditions. This means engines can be tuned far more adventurously to drive up fuel efficiency, by as much as eight per cent above non-SCR engines.
Sigma also consumes less Adblue, and it requires less regular maintenance because it does not produce hard deposits.
Sigma is far smaller than wet systems because: the ammonia gas can be dosed very close to the catalytic converter; its efficiency meant the size of the catalytic converter can be greatly reduced; and it has fewer moving parts.
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