Abstract
Keywords: NOx emission, oxygen conductors, thermoelectric materials
The numerous advantages of the compression ignition engines have made that these engines are widely used for driving the vehicles. It is important to notice a very dynamic increase in share of these engines in a group of vehicles of LDV, which is recently observed. According to the forecast as soon as next year a half of newly-sold passenger cars in Europe will be equipped with driving units of such a type. Moreover, it is known that the compression ignition engines are the dominant source of driving for HDV, off-road vehicles, and vessels.
At present the most important factor determining the development of diesel engines is the environmental protection and the Earth´s natural resources. Unfortunately, it should be emphasized that the diesel engine is one of the main sources of the natural environment degradation. Its negative effect on the human body is not also out of importance.
At present stage of development one of the main challenges is lowering the PM and nitrogen oxides NOx emission especially from the compression ignition engines. The implementation of more and more rigorous standards limiting the emission level and the growing social ecological awareness faced the designers and manufacturers to undertake the actions aiming to limit the emission of toxic exhaust gas compounds. Thereby it involved the necessity for using the complex solutions, which can be divided into three main groups:
o A direct treatment of the combustion process, which is a source of forming the toxic compounds. The example action of such type is, among others, combustion of a homogeneous charge.
o Affecting the exhaust gas after the engine cylinder, i.e. exhaust aftertreatment. Such action as, among others, the selective catalytic reduction, using the Diesel Particulate Filters should be included into this group.
o Use of suitable fuels with lower sulphur content, for example.
Only combined use of solutions included into the groups stated above and their continuous development will ensure the compression ignition engines to be successful on the market. Some time ago the engine designers have already observed the potential possibilities of the widely understood conception of the fuel injection (i.e. fuel injection system design solution, injection characteristics). These observations resulted in a very dynamic development of the injection systems being noticed during several last years, mainly the Common Rail ones, which are dominant in case of the compression ignition engines.
One of the most popular methods of NOx emission reduction is the use EGR or a catalyst located in the engine´s exhaust system. A less popular and more technically challenging solution is the use of a system mounted in the exhaust part of the engine consisting of an injector that distributes a reducing agent, usually ammonia, to the exhaust manifold. In order to solve the problem of NOx emission in a manner proposed herein, the following key assumptions need to be addressed:
reducing nitrogen oxides emissions by a total elimination of nitrogen from the engine feeding system with the use of an oxygen separator,
harnessing the engine´s waste heat to feed a separator system with the use of thermoelectric materials.
The idea is based on a quite simple notion that the absence of nitrogen in the engine feeding system is a condition sufficient to a total elimination of nitrogen oxides from the exhaust gases. The concept as such is not new at all. There has been an idea of eliminating nitrogen from the atmosphere by the use of absorbers, but so far with no practical application whatsoever. The authors believe that new ceramic materials enable the concept presented to be realized in an original and innovative way.