It is because of thinner air and lower temperature at high altitude, a good rule of thumb for most generators is that you will lose 10% of the rated output every time you gain 3,000' (1foot=3.048m) in altitude. This means that a 10,000 watt generator running at9,000' of altitude will only be capable of producing 7,000 watts at that altitude. More air is needed for combustion at the high altitude as the air becomes thinner. This phenomenon is generally experienced by the recreational vehicle travelers. In the highland series of EFIgenset, a turbocharger is employed to compress more air flowing into the engine. Electronic fuel injection (EFI) controls the fuel mixture with the best AFR to be burned completely to produce greater power from each explosion within the cylinder.
The conventional carbureted generator does not have the luxury of an Engine Control Unit (ECU) like the one in EFIgenset. The major shortfall of non-EFI propane engine ishard starting. Propane enters the combustion chamber in a vapor form. Vaporvolumetric measurement is greatly affected by temperature and altitude. This causes air fuel ratio change to too rich or too lean for the engine to burn. If a propane engine is well tuned in Chongqing, it may not start well and run well in high altitude Yunnan when temperature and altitude change. The same generator is tuned well in California may not start and run well on the peak of the Rockies. This phenomenonhas small impact on liquefied propane that run on sequential electronic fuel injection engine. Vapor propane engine requires constant adjustment to the pressure regulator to provide appropriate mixture. Just imagine there are hundreds of these propane generators scattered around different telecom base stations on the high altitude locations, it make the maintenance work extremely difficult and expensive.
Experts estimate that normal atmospheric pressure at sea level is roughly 14.7 pounds per square inch (psi, which is the equivalent of roughly 1 bar) and that a turbocharger can compress the air by 6 to 8 psi (0.4 to 0.55 bar). This means that a turbocharger can pump roughly twice as much air into the engine. Since the system isn't 100 percent efficient, the engine will probably get a 30 to 40 percent boost in power, rather than a 50 percent boost.
Our standard 1.0L EFIgenset genset outputs 15kW of continuous power versus the highland series of the same model that outputs 20kW of continuous power by turbocharged engine at sea level. However, power output will be reduced when the generator is moved to a higher altitude.
Below examples are extracted from
The following example assumes the same engine speed and air temperature.
Condition 1:
An engine operating at wide open throttle (WOT) on top of a very high mountain has a manifold pressure of about 50 kPa (essentially equal to the barometer at that high altitude).
Condition 2:
The same engine at sea level will achieve 50 kPa (7.25 psi, 14.7 inHG) of manifold pressure at less than WOT due to the higher barometric pressure.
The engine requires the same mass of fuel in both conditions because the mass of air entering the cylinders is the same.
If the throttle is opened all the way in condition 2, the manifold absolute pressure will increase from 50 kPa to nearly 100 kPa (14.5 psi, 29.53 inHG), about equal to the local barometer, which in condition 2 is sea level. The higher absolute pressure in the intake manifold increases the air's density, and in turn more fuel can be burned resulting in higher output.
Another example is varying rpm and engine loads -
Where an engine may have 60kPa of manifold pressure at 1800 rpm in an unloaded condition, introducing load with a further throttle opening will change the final manifold pressure to 100kPa, engine will still be at 1800 rpm but its loading will require a different spark and fueling delivery.
Vacuum comparison
Engine vacuum is the difference between the pressures in the intake manifold and ambient atmospheric pressure. Engine vacuum is a "gauge" pressure, since gauges by nature measure a pressure difference, not an absolute pressure. The engine fundamentally responds to air mass, not vacuum, and absolute pressure is necessary to calculate mass. The mass of air entering the engine is directly proportional to the air density, which is proportional to the absolute pressure, and inversely proportional to the absolute temperature.