Given the ever more stringent emission regulations modern diesel engines undergo these days, the need for advanced EGR systems becomes crucial in all major applications, in particular on- & off-road commercial diesel engines. One of the key aspects of these so-called advanced EGR systems thereby is to reliably provide the engine with the appropriate, high amounts of EGR over the entire range of operating conditions. Whereas common systems are either optimized for low-torque/low-speed operating conditions, or a narrow range around one specific engine speed, the advanced systems aim to both cover the entire operating range and significantly increase the current level of EGR. The advanced EGR systems developed at MAHLE make use of two types of fast acting devices in a modular approach. Depending on the engine size/layout and the amount of EGR needed, the devices are either placed directly in the EGR line or the intake manifold. Using the latest technical advances in mechatronics, the oscillating valves can be opened or closed within less than 3ms, which makes it not only possible to accurately control the amount of EGR fed back into the engine, it also allows to boost the amount of EGR using the exhaust pressure oscillations. In addition to these oscillating valves, rotational flaps have been developed to significantly reduce the complexity of the systems, while still offering similar benefits in terms of EGR rates and variability. Shown hereafter are the results from thorough investigations conducted on both European and US heavy-duty diesel engines. Focusing on some of the most common engine characteristics, such as EGR rates, emissions of nitrogen oxide and fuel consumption, significant benefits can be seen using the newly developed technologies. Compared to conventional measures, such as increased exhaust backpressure and/or constant charge-air throttling, the advanced systems prove to be both more efficient and flexible in terms of EGR rates, as well as beneficial regarding some of the most important engine characteristics.
Foreword for Special Issue “New Outlook on Combustion Technologies to Overcome Future Emission Regulations”