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- How to produce as much steam as possible from exhaust gas + water in engine exhaust pipe?

Hi all,

The idea is to generate as much as possible water steam from heat of internal combustion engine exhaust gas. The so called steam generation device is a simple sloped engine exhaust pipe where water from engine cooling and hot gas is fed at the top and all the mix is exiting at the bottom.

I would like to have some basic napkin calculations for the ballpark numbers and practical cost effective idea to build it in reality.

The natural "product" in real life of such thing is not much water vapor but pretty much hot water and still hot gas (above water boiling point) in non uniform mix.

P.s. we are NOT talking about specialty marine wet exhaust systems, where the gas is bathed in cool water and exits in temperatures very close to ambient.

I would like to split the question into physics and engineering exercises.

Physics/thermodynamics:

The pretty close figures to real life of diesel engine running at some load:

V

V

t

t

L - length of the pipe = 2 m

R - inner radius of the pipe = 0.05 m

V - total volume of the pipe = 0.0157 m

Pipe is sloped at 30 degrees.

The consensus on various reports is that the exhaust gas from IC engine has physical properties very close to air.

At 800K, air has:

ρ - density = 0.435 kg/m

h - specific enthalpy = 822.5 kJ/kg

s - specific entropy = 7.888 kJ/(kg·K)

C

k - thermal conductivity = 0.0577 W/(m·K)

I have not found the "quick and dirty" list of water properties, but will update post, if necessary.

Lets assume, that heat loses from pipe external thermal radiation is 0, pressure in pipe is atmospheric or very close to atmospheric if that can be possible in real life.

From my understanding to solve this exercise I have for the beginning to know how much water is in the pipe at any time, then my knowledge stops: is there a specific heat of air and water + specific heat of the water to boil or thermal conductivity I have to calculate? There is a time constraint also, as in real life exhaust is supplied with new air and water constantly.

Maybe just assume that the ratio water : air is 5 : 400 and thats it?

Engineering:

The question is what is of the most importance: Make pipe slope as little as possible to slow water? Volume of the exhaust pipe? Somehow my guts tell me do not bother with welding some strange additional metal boxes and limit the amount of water to the just exact amount to boil it and that is.

Maybe I can have ballpark numbers how long and wide a pipe should be for the amount of water coming in for the max amount of hot water vapor?

I do not have spare engine at hand to make practical experiment :(

Thank you for your calculations and ideas.

This is my first post, and I am not much into physics/thermodynamics. Thank you all for replies.

The idea is to generate as much as possible water steam from heat of internal combustion engine exhaust gas. The so called steam generation device is a simple sloped engine exhaust pipe where water from engine cooling and hot gas is fed at the top and all the mix is exiting at the bottom.

I would like to have some basic napkin calculations for the ballpark numbers and practical cost effective idea to build it in reality.

The natural "product" in real life of such thing is not much water vapor but pretty much hot water and still hot gas (above water boiling point) in non uniform mix.

P.s. we are NOT talking about specialty marine wet exhaust systems, where the gas is bathed in cool water and exits in temperatures very close to ambient.

I would like to split the question into physics and engineering exercises.

Physics/thermodynamics:

The pretty close figures to real life of diesel engine running at some load:

V

_{w}- volume (flow) of water per second = 0.0005 m^{3}/sV

_{a}- volume (flow) of air per second = 0.04 m^{3}/st

_{w}- temperature of water entering the pipe = 310 Kt

_{a}- temperature of air entering the pipe = 800 KL - length of the pipe = 2 m

R - inner radius of the pipe = 0.05 m

V - total volume of the pipe = 0.0157 m

Pipe is sloped at 30 degrees.

The consensus on various reports is that the exhaust gas from IC engine has physical properties very close to air.

At 800K, air has:

ρ - density = 0.435 kg/m

^{3}h - specific enthalpy = 822.5 kJ/kg

s - specific entropy = 7.888 kJ/(kg·K)

C

_{p}- specific heat at constant pressure = 1.099 kJ/(kg·K)k - thermal conductivity = 0.0577 W/(m·K)

I have not found the "quick and dirty" list of water properties, but will update post, if necessary.

Lets assume, that heat loses from pipe external thermal radiation is 0, pressure in pipe is atmospheric or very close to atmospheric if that can be possible in real life.

From my understanding to solve this exercise I have for the beginning to know how much water is in the pipe at any time, then my knowledge stops: is there a specific heat of air and water + specific heat of the water to boil or thermal conductivity I have to calculate? There is a time constraint also, as in real life exhaust is supplied with new air and water constantly.

Maybe just assume that the ratio water : air is 5 : 400 and thats it?

Engineering:

The question is what is of the most importance: Make pipe slope as little as possible to slow water? Volume of the exhaust pipe? Somehow my guts tell me do not bother with welding some strange additional metal boxes and limit the amount of water to the just exact amount to boil it and that is.

Maybe I can have ballpark numbers how long and wide a pipe should be for the amount of water coming in for the max amount of hot water vapor?

I do not have spare engine at hand to make practical experiment :(

Thank you for your calculations and ideas.

This is my first post, and I am not much into physics/thermodynamics. Thank you all for replies.