CNG gas temperature right after it exits the DI nozzle
CNG gas temperature right after it exits the DI nozzle
(OP)
Hi everyone,
I need some information on the items below: -
1) Compressed CNG from a high pressure tank at 200 bar, 25 degree C being injected into an engine cylinder through a DI injector. No regulator to bring down the feed pressure. What will be the temperature of the methane gas right after it gets out of the DI nozzle
2) What will be the gas pressure during this time?
The complication that I have is that the gas expands a lot as it goes out from the high pressure line to the cylinder. However, there is also some heat transfer from the tip of the nozzle which can go up as high as 250 degree C. Will the methane gas drops below 0 degree C?
I need some information on the items below: -
1) Compressed CNG from a high pressure tank at 200 bar, 25 degree C being injected into an engine cylinder through a DI injector. No regulator to bring down the feed pressure. What will be the temperature of the methane gas right after it gets out of the DI nozzle
2) What will be the gas pressure during this time?
The complication that I have is that the gas expands a lot as it goes out from the high pressure line to the cylinder. However, there is also some heat transfer from the tip of the nozzle which can go up as high as 250 degree C. Will the methane gas drops below 0 degree C?





RE: CNG gas temperature right after it exits the DI nozzle
For example throttling valves are typically considered to have a constant enthalpy pressure drop across them. An example of this is found in a car's air conditioning system and is called an expansion valve.
An example of a constant entropy designed valve would be a properly engineered pressure safety valve. These valves are designed such that they approach an isentropic process.
With the above information, you should be able to answer your own question. I do not have detailed knowledge of a DI injector; however, I would guess that it might approach a constant entropy design. If you carefully look at the injector's design, it should have a diverging nozzle to expand the gas if creates an isentropic drop.
RE: CNG gas temperature right after it exits the DI nozzle
RE: CNG gas temperature right after it exits the DI nozzle
I have the property table of Methane but I couldnt figure out on how to calculate the temperature change as it exits the nozzle.
RE: CNG gas temperature right after it exits the DI nozzle
P1 = 30 psig, T1 = -40 degC, then h1 = 12.285.
if P2 = 0 psig and isenthalpic process (h1 = h2), then T2 = -41.5 degC.
RE: CNG gas temperature right after it exits the DI nozzle
A Pressure-Enthalpy graph and data for methane is available in
ASHRAE Handbook, Fundamentals Volume - available in any engineering library.
ASHRAE = American Society of Heating, Refrigerating and Air-Conditioning Engineers
RE: CNG gas temperature right after it exits the DI nozzle