te72:
you are thinking of gauge pressure. yes 12 psi is 12 psi is 12 psi....that is 12 psi GAUGE. difference between gauge pressure and absolute pressure is the key. your gauge will go from vacuum to 0 psi. at 0 psi you are at atmospheric pressure. at 6000', atmospheric pressure is 12.8 or so psi. 1 psi on the gauge would be 13.8 psi absolute or 1 psi over atmospheric pressure. that is still less than the pressure at sea level. Theoretically, if you were to boost 2 psig at 6000' you would be at the same power level as sea level if you weren't to boost at all. that is the concept of turbo-normalized aircraft. the aircraft holds a specific manifold ABSOLUTE pressure (map). maintaining map at a specific pressure would give x hp to a critical altitude.
te72 & CyFi6:
most wastegates are rated at gauge pressures not absolute pressures. most car wastegates use gauge pressure to control boost. because of that, a car wastegate will not equal things out with atmospheric pressures.
energy moves things. that includes compressing the air in the turbocharger. how do you increase energy from an engine? add more air molecules. think of the wastegate as how much energy you are throwing away from the exhaust. you are higher in altitude thus not as much air molecules. the lack of air molecules means less energy. the decrease in energy means slower spool.
it doesn't matter if you have a wastegate in the equation or not or if the air is being compressed (up to an extent) or not. the thermodynamics will still hold. yes atmospheric o2 is not a real ideal gas but for calculation purposes it is close enough (you could use Van der Waals equation of state to get a better prediction). the ideal gas law will deviate away from it's prediction at high pressures like 10 atm and low temperatures. why? at high pressures the size of the molecule needs to be taken into account. the volume at high pressures will be higher than predicted because of the size of the molecules. at low temperatures the molecules aren't moving as fast. so intermolecular forces need to be taken account. the volume at low temperatures will be smaller than predicted because the molecules want to come together. why am i talking about volume prediction and how does that relate to anything? PV=nRT, volume is directly proportional to number of moles of a gas meaning lower V then lower n and vice-versa. A turbocharger does not produce 10 atm (140 psi or so) of pressure and charge temperatures are not low temperatures.
Grandavi:
great way of thinking about work/energy for the turbocharger.
you are thinking of gauge pressure. yes 12 psi is 12 psi is 12 psi....that is 12 psi GAUGE. difference between gauge pressure and absolute pressure is the key. your gauge will go from vacuum to 0 psi. at 0 psi you are at atmospheric pressure. at 6000', atmospheric pressure is 12.8 or so psi. 1 psi on the gauge would be 13.8 psi absolute or 1 psi over atmospheric pressure. that is still less than the pressure at sea level. Theoretically, if you were to boost 2 psig at 6000' you would be at the same power level as sea level if you weren't to boost at all. that is the concept of turbo-normalized aircraft. the aircraft holds a specific manifold ABSOLUTE pressure (map). maintaining map at a specific pressure would give x hp to a critical altitude.
te72 & CyFi6:
most wastegates are rated at gauge pressures not absolute pressures. most car wastegates use gauge pressure to control boost. because of that, a car wastegate will not equal things out with atmospheric pressures.
energy moves things. that includes compressing the air in the turbocharger. how do you increase energy from an engine? add more air molecules. think of the wastegate as how much energy you are throwing away from the exhaust. you are higher in altitude thus not as much air molecules. the lack of air molecules means less energy. the decrease in energy means slower spool.
it doesn't matter if you have a wastegate in the equation or not or if the air is being compressed (up to an extent) or not. the thermodynamics will still hold. yes atmospheric o2 is not a real ideal gas but for calculation purposes it is close enough (you could use Van der Waals equation of state to get a better prediction). the ideal gas law will deviate away from it's prediction at high pressures like 10 atm and low temperatures. why? at high pressures the size of the molecule needs to be taken into account. the volume at high pressures will be higher than predicted because of the size of the molecules. at low temperatures the molecules aren't moving as fast. so intermolecular forces need to be taken account. the volume at low temperatures will be smaller than predicted because the molecules want to come together. why am i talking about volume prediction and how does that relate to anything? PV=nRT, volume is directly proportional to number of moles of a gas meaning lower V then lower n and vice-versa. A turbocharger does not produce 10 atm (140 psi or so) of pressure and charge temperatures are not low temperatures.
Grandavi:
great way of thinking about work/energy for the turbocharger.
