Industrial engines are generally used in packages with electrical outputs above 150-200kW. Automotive derived engines are the most widely used engines for smaller systems up to 200kWe and there is now considerable operating experience in terms of their reliability and maintenance. When used in cogeneration systems, these engines are based on modified truck engines converted to run on gas. The engine life, as a cogeneration unit, when measured against that of its automotive equivalent, is considerably extended, as is the interval between servicing. This is achieved by running at a much slower and constant speed, typically 1500rpm under steady conditions. Engine life is shorter than that of the industrial engine, generally 20,000-30,000 hours before a full engine overhaul.
Larger units have a longer life.
The most common diesel engines, other than those in road vehicles, are those fitted to standby generator sets installed to protect vital services. The fuel options are usually limited to diesel. Although standby generators are often based on industrial diesel engines, when considering a particular engine, its history, pedigree and condition should be carefully evaluated before any conversion because low use does not necessarily mean the engine is in peak condition. The primary considerations for cogeneration are not necessarily the same as for standby operation. In particular, standby generators are generally larger than required for optimum cogeneration operations.