Benefits of exhaust gas recirculation from mtu
Generally speaking, systems designed to reduce emissions must be modified to match the drive systems. mtu
has produced a very compact design that permits all the exhaust gas recirculation components to be integrated into the engine concept (see Figure 1), so that any modifications to the engine have relatively little effect on space requirements and the exhaust system. It is necessary to modify the radiator, however, in order to cope with the increased cooling capacity of the engine. Compared to engine modifications involving an SCR system, this makes it much easier for customers to convert their units to meet new emissions standards because EGR systems for reducing nitrogen oxides require no additional operating media and thus involve no further expense or work on extra tanks and lines. The customer
benefits in terms of reduced costs for handling and maintenance.
Principle of operation
In exhaust gas recirculation, some of the exhaust gas is drawn off from the exhaust system, cooled and redirected back into the cylinders (see Figure 2). Although the exhaust fills the combustion chamber, it is not involved in the combustion reaction that takes place in the cylinder due to its low oxygen content. The speed of the combustion
process overall is thus reduced, with the result that the peak flame temperature in the
combustion chamber is lowered. This dramatically reduces the production of nitrogen oxides.
Patented solution from mtu: the donor cylinder concept
Exhaust gas recirculation places higher demands on exhaust gas turbocharging, since
higher boost pressures have to be achieved with reduced mass flow in the turbocharging system. These high boost pressures are required to direct
the increased mass flow resulting from the exhaust gas recirculation rate into the cylinder during the gas cycle. In addition, the exhaust gas can only be redirected back into the cylinders when there is a pressure drop between the exhaust and the charge air systems. This pressure drop must be established with an appropriately configured turbo charging system, which results in a reduction in turbocharging efficiency. The pressure drop between the exhaust and the charge air systems leads to gas cycle los - ses. These factors tend to result in lower engine performance or higher fuel consumption. To improve the combined effect of exhaust gas recirculation and turbocharging, mtu
has developed what is known as the donor cylinder exhaust gas recirculation system (see Figure 3). mtu
’s patented system only uses some of the engine’s cylinders as the donor for exhaust gas recirculation. An exhaust valve (donor valve) holds back the exhaust gas flow downstream of the donor cylinders and thus creates the necessary pressure drop between the exhaust and the charge air systems. This means that the turbocharging system can be optimized to a very good efficiency level, with gas cycle losses only affecting the donor cylinders. Compared with conventional high-pressure exhaust gas recirculation (as in the case of the Series 1600 engine), the donor cylinder concept (Series 2000 and 4000) achieves lower fuel consumption, since it reduces the gas cycle losses in the engine and permits higher turbocharger efficiency levels. For this purpose, an additional donor cylinder exhaust valve is required in comparison with high-pressure exhaust gas recirculation. Dirt build-up on components and the amount of servicing required over the service life of the application are lower with the donor cylinder concept, as is the case with high-pressure exhaust gas recirculation: unlike the situation with low-pressure exhaust gas recirculation, the exhaust gas is not fed into the intake air until immediately
before it enters the cylinder, which means that only clean air flows through the
compressor impeller and the intercooler and not exhaust gas containing particles as well.