They go by the name of soot particles or nitrogen oxides, particulate filters, SCR catalytic converters or exhaust gas recirculation systems – buzz words that keep engine specialists occupied. While the power output and the efficiency of an engine was the main interest a few years ago, a third component has now been added: exhaust emissions. Maximum emission levels are different depending on the region, but they all have one thing in common: they specify the emission levels of nitrogen oxides (NOx) and soot particles (PM). By the year 2014, these limits will in many countries go down to a fraction of what they were at the beginning of the new millennium.
Diesel engines are thermal engines with the highest efficiency level. However, pollutants are produced during the combustion process. For this reason, back in the 1980s, MTU began to reduce engine emissions. With the perfect combination of key technologies that had been developed and produced in-house, such as turbocharging, fuel injection, engine electronics and exhaust aftertreatment.

Turbocharging, injection and exhaust gas recirculation
The performance of an internal combustion engine can be increased by adding turbocharging. A turbocharger compresses the air so that more oxygen flows into the combustion chamber. In this way, more fuel is burned and the power output of the engine increases accordingly. The turbocharger is driven by exhaust gas, which makes turbocharged diesel engines very efficient. MTU develops this key technology for high-performance engines in-house.

With common rail fuel injection, the combustion process can be optimized to achieve low pollutant levels combined with lower fuel consumption. Fuel is injected into the combustion chamber from a common rail under high pressure. The electronic control system ensures that the start of injection, the quantity and time are independent of the engine speed. In 1996, with the Series 4000 engine, MTU was the first manufacturer of large diesel engines to introduce common rail fuel injection as a standard feature.

Nitrogen oxide (NOX) emissions can be reduced using internal engine technology by cooling some of the exhaust gas, which is then redirected back into the charge air. This results in the reduction of the combustion temperature and less nitrogen oxide is produced. This process is known as exhaust gas recirculation (EGR) and is one of the principal methods used to reduce nitrogen oxide emissions from diesel engines. MTU has been testing this key technology for years. As a standard feature, it will be included for the first time in Series 4000 engines — starting mid-2011 in oil & gas engines for hydro frac applications to ensure compliance with EPA Tier 4 interim emission standards, followed by rail applications who need to meet EU Stage IIIB emission standards which come into force in 2012.

Electronic control unit
The brain of a modern engine is the electronic control unit. It monitors and controls all the key functions of the engine and the exhaust aftertreatment system. The control unit also acts as the interface to the vehicle’s automation system. The optimum interplay of the entire drive system is the key to low pollutant emissions, low fuel consumption and high power output over the entire service life. MTU develops and manufactures this key technology in-house.

Diesel particulate filter and Selective Catalytic Reduction
A diesel particulate filter (DPF) can remove virtually all the soot particulates (PM) from the exhaust gas emitted from a diesel engine to ensure compliance with very strict emission standards. Regardless of the actual emission limit, diesel particulate filters satisfy the needs of operators who place importance on achieving extremely low soot emissions.

The term Selective Catalytic Reduction (or SCR) is used to describe a chemical reaction in which harmful nitrogen oxides (NOx) in exhaust gas are converted into water (H2O) and nitrogen (N2). In combination with internal engine technologies, such as exhaust gas recirculation (EGR), extremely low nitrogen oxide emissions can be achieved with low fuel consumption.