Dilemma posed by the euro 4 and euro 5 directives
The Euro 4 Directive poses a problem for Iveco – and other manufacturers too – that is difficult to resolve, namely, to reduce particulate emissions by 80% and nitrogen oxides by 30% compared to Euro 3 levels. The Euro 5 Directive then requires a further 40% reduction for nitrogen oxides. Today, given current know-how and fuel injection technologies, action taken on the combustion front can only reduce the percentage of one pollutant by increasing the emissions of the other. This is why exhaust gases must be subjected to exhaust after-treatment in order to complete action taking place within the engine. The same situation exists as regards compliance with Euro 5 emission limits.
At this point manufacturers have two options. The percentage of nitrogen oxides in the combustion chamber can be reduced by lowering temperatures as a result of adding exhaust gases to air aspirated at the time of combustion. These gases, which replace part of the engine's air intake, must be carefully dosed and cooled inside a heat exchanger fed by the engine cooling system. Simultaneously, injection timing is retarded. However, any drop in combustion temperature causes a drop in engine efficency. The other problem is a marked increase of particulate matter in the exhaust, especially in recirculated exhaust gases. This can lead to contamination of the lubricant, which must therefore have a greater particulate dispersion capacity. Particulate is treated after the engine stage by using a filter in the exhaust silencer. While these factors have little effect on low-capacity engines, the impact becomes significant as engine power increases. Exhaust gas recirculation is referred to as EGR. Recently this solution has been adopted by some manufacturers on medium and heavy trucks in order to meet Euro 4 standards. For Euro 5, given current technologies the EGR + particulate filter system is not sufficiently effective for high-powered engines, even though this solution doesn't require the addition of an additive to the exhaust. Compared to Euro 3, the EGR solution means an increase in vehicle weight.
The SCR – Selective Catalytic Reduction – solution is the alternative approach chosen by Iveco and the majority of medium and heavy commercial vehicle manufacturers. It consists of optimising engine combustion to achieve maximum reduction of the particulate content in exhaust gases. Engine performance is improved and this leads to lower fuel consumption. To eliminate the percentage of nitrogen oxides in exhaust gases that exceed the limit, first a reducing agent is added to the gases and then these are treated by a catalytic filter in the silencer. This procedure converts the nitrogen oxides into entirely harmless nitrogen and water vapour. The reducing agent is ammonia, stored in the form of a urea-based aqueous solution and marketed under the brand name AdBlue. SCR technology means that particulate filtration is superfluous inasmuch as this type of emission is cut down directly during the combustion phase, while the catalytic converter burns up the remaining particulate simultaneous with treatment of the nitrogen oxides.
Again in this case the vehicle weight increases compared with an equivalent Euro 3 version.