Determining Water Horse Power, Total Dynamic Head and Engine Brake Horse Power needed:
Efficiency : Reciprocating engines are highly efficient. Technology enhancements such as better combustion chamber design and controls that constantly optimize the air-fuel ratio increase engine efficiency. Engine efficiencies nowadays are at about 45% for larger units.
Reliability: There have been many technical improvements that have improved engine reliability as well as extended the equipment life. Improvements in ceramic valve seat materials can easily double the life of engine valves between overhauls. This extends engine cylinder thus reducing maintenance costs and engine downtime.
Air quality : Engine emissions in general are decreasing for all prime-mover technologies. However, these emissions vary primarily with combustion technology and fuel. Advances in combustion chamber design, improved catalysts and sophisticated air-fuel ratio controllers all contribute to the ongoing reduction of engine exhaust emissions. Most natural gas engine NOx emissions are currently at 1 gram per hp-hr and expected to be at 0.5 gram per hp-hr by 2010.
Noise : As the engine output increases, noise levels go up too. An unenclosed engine generates about 100 decibels (dBA) at 33 feet. Engines have always been noisy but improvements in sound enclosures have helped mitigate the noise level down to 65 dBA or less which is what you would hear if you stood next to an operating residential a/c unit.
Maintenance : Maintenance costs for engines range from .9c to 1.3c per hp-hr. Engine manufacturers have been working hard to improve engine components such as longer-life, better performing spark plugs, electronic ignition systems that allow better control of engine output emissions, reduced valve maintenance and improved oils. All the above in turn, prolong maintenance intervals.