Generators powered by internal combustion engines are very widely used and in many cases the harmful exhaust emissions from them are a concern.
Standby diesel generators often require planning permission and this may stipulate that they comply with very strict air quality standards, especially if they are located at ground level in an urban area. Another issue with standby generators is that they usually require periodic testing and if the exhaust is unpurified this may result in complaints from neighbours and the triggering of smoke detectors. A further problem is that soot in diesel exhaust rapidly blackens walls in close proximity to the exhaust outlet and in a prestigious building can necessitate expensive cleaning, sometimes just as a consequence of commissioning the system.
The exhaust emissions from mobile generators are also very important in certain situations, for example at an open air festival a lot of people will be in close proximity, whilst if a mobile generator is used to provide temporary power in response to a grid failure it may well spend a considerable time operating in a residential area. In either of these examples, the environmental impact clearly needs to be minimised.
Generators used in distributed power plants are likely to be larger and to clock up far more hours per year than either standby or mobile units, and for these reasons their exhaust emissions require careful consideration. One increasingly popular variation on distributed power is combined heat and power, which often receives grant funding because of its capacity to reduce carbon dioxide emissions. Understandably, this grant funding usually imposes strict limits on the toxic emissions in order to prevent them outweighing the benefits of the reduction in carbon dioxide.
(Photo: Exhaust systems incorporating diesel particulate filters for a pair of 400 kVa standby generators)