PDF Book on Triple and Quadruple Expansion engines

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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cyberbadger
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Re: PDF Book on Triple and Quadruple Expansion engines

Post by cyberbadger » Wed Jan 11, 2017 7:37 am

Well here's some mud to clear the water ..

I have for my own amusement run the steam exhaust of an engine to the steam intake of another. Efficient/Practical - heck no. Showing double expansion - yes.

What would it have done if the pipe connecting the two had a series of blow torches pointed at it - would that cause the engines to run differently? (faster?)

-CB
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Re: PDF Book on Triple and Quadruple Expansion engines

Post by RGSP » Wed Jan 11, 2017 10:53 am

cyberbadger wrote:
What would it have done if the pipe connecting the two had a series of blow torches pointed at it - would that cause the engines to run differently? (faster?)

-CB
Yes, faster. Same pressure but more volume.

For what it's worth, reheating is comparable to combustion in a jet engine - no significant pressure change, but much more volume out than volume in, and hence net work out.
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Re: PDF Book on Triple and Quadruple Expansion engines

Post by Lopez Mike » Wed Jan 11, 2017 2:37 pm

Thank you Fred.

As much as I have been dealing with it for an embarrassing number of years, I still find it sort of weird that superheated steam doesn't obey Boyle's law.

I'm quite thankful that my primitive power plant is largely devoid of such issues. For me the extra fuel consumption is a small price to pay for hassle free operation.
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Re: PDF Book on Triple and Quadruple Expansion engines

Post by DetroiTug » Wed Jan 11, 2017 3:41 pm

Fred,

I've never checked the pressure at the orifice, but it definitely appears to run at more pressure than 50 psi air pressure when vaporizing. When I run out of fuel and there is nothing but air, it appears to be much lower pressure/velocity. Keep in mind, this burner uses two separate fuel sources. The heat impinged on the vaporizer can be controlled independently of the main burner flame. There are times, depending on the amount of heat impinged on the vaporizing coil, the burner does fluctuate between high and low flame. We work to find a balance with amount of heat on the vaporizer and reasonable main burner orifice size for whatever type of driving. .035~ for parades, .040 for general driving and .042+ for racing. :) And of course too much heat on the vaporizer, then the fuels breaks down to carbon and typically clog the orifice, which I remedied by installing a brass screen just before the orifice, works great.

-Ron
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Re: PDF Book on Triple and Quadruple Expansion engines

Post by fredrosse » Wed Jan 11, 2017 5:24 pm

The liquid fuel circuit, I assume, is a pressurized tank, 50 psi compressed air over the water. When you are vaporizing fuel in the coil, a very small volumetric flow (say 1 gallon per hour) of fuel oil enters the coil, where it is boiled away into a much much larger volumetric flow of vaporized fuel, say 30 gallons per hour of vapor. In this case the high volumetric flow of vaporized fuel creates a high pressure drop in the discharge orifice, and the vaporizing coil pressure is close to, but slightly less, compared to the 50 psi driving pressure feeding the vaporizing coil. Pressures thru the system might be: 50 psi in the fuel tank, 49 psi at the inlet to the vaporizing coil (small fuel lines), then 48 psi on the fuel vapor nozzle, discharging to 0 psi in the burner.

When air is passing thru the system, the large change in volumetric flow will not occur. Perhaps 1 cubic foot per hour of cool air from the tank into the vaporizing coil, and, with coil artifically heated, perhaps 2 cubic feet of hot air passing thru the fuel vapor nozzle. This moderate expansion in volumetric flow is only due to heating of the air, no phase change. Under this condition the pressure drops are more evenly divided, perhaps the distrubition as follows: 50 psi in the fuel tank, 20 psi at the inlet to the vaporizing coil (small fuel lines), then 18 psi on the fuel vapor nozzle, discharging to 0 psi in the burner. This lower pressure at the fuel nozzle occurs because there is no boiling (with subsequent large volumetric expandion) in the vaporizing coil. Air does not experience a phase change from liquid to gas.
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Re: PDF Book on Triple and Quadruple Expansion engines

Post by DetroiTug » Wed Jan 11, 2017 10:21 pm

Fred,

Thanks, your explanation makes sense, I see it now. The higher volumetric flow of gas vs liquid or air which is considerably lower gives the appearance of higher pressure. I was visualizing all sorts of phenomenon like raising the pressure in the fuel tank over time etc I'd never need to add air. :D

There are two fuel systems, one for Kerosene (main burner 50 psi) and white fuel for the pilots which is ran at 15 psi. There is a main air tank at ~100 psi and then a regulator for each fuel tank set to the respective pressures, so the fuel pressures remain constant.

Thanks, Ron
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Re: PDF Book on Triple and Quadruple Expansion engines

Post by fredrosse » Thu Jan 12, 2017 4:30 am

Your new vaporizing burner is a fine piece of work, and works very well from what I have seen in your videos. I hope to build something similar, only smaller for a Bolsover Boiler which is only about 10 inches square, 12 inches high.
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Re: PDF Book on Triple and Quadruple Expansion engines

Post by DetroiTug » Fri Jan 13, 2017 4:24 pm

Fred,

"build something similar, only smaller"

Should be able to scale that down. For a vaporizer in one test and it withstood the heat, I used 8mm 5/16" Cunifer brake line. Stainless steel is best.

Burners are a mysterious science, it's mostly trial and error. Just observe some basics plenty of air without restriction in the mixing tube (throat), no flame impinged on the burner chamber or branches as it will ignite the fuel internally and create a "backfire", adequate heat on the vaporizer coil. Fuel type really matters, white fuels are the easiest to vaporize, hexane is even easier but difficult to obtain. The heavier the fuel, the more vaporization surface area/heat is needed. Kerosene and Fuel oil/deezel, require the most. Many of these type burners are touted as multi-fuel and that really isn't true as in the case of the Baker types where the majority of vaporization happens over the main burner flame, it's going to do one fuel type well and another not-so-good or too much, why a lot users mix gasoline and kerosene together to find a balance to eliminate carbon production within the vaporizer. The burner above does 90% of the vaporization independent of the main burner flame, so the heat on the vaporizer can be controlled for fuel type, it really is a multi-fuel burner as it can be adjusted to the fuel type.

-Ron
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Re: PDF Book on Triple and Quadruple Expansion engines

Post by TriangleTom » Thu Jun 22, 2017 10:11 pm

Sorry to resuscitate an old thread, but as I'm getting close to finishing my engine design I thought that I'd clear a few things up when I refer to steam reheat.

In my engine design, which is quadruple expansion, the steam reheat takes place between the LP cylinder on the HP side (second steam expansion) and the HP cylinder on the LP side (third steam expansion) cylinders, at a pressure of about 120 PSI. The pressure of the steam in the line will actually fall by a few PSI between the two due to head losses caused by the routing of the steam back to the flue and then back to the engine, but the volume of the steam will increase tremendously as it goes from saturated 341 F @ 120 PSI to superheated at 450 F at the same pressure. This allows more energy to be extracted from the steam. Essentially, think of it as just increasing the volume of the steam so that it can exert the same pressure over a greater area in the three (see below) cylinders on the low pressure side of the engine.

Three cylinders are used in the LP, reheated section of the engine because as the volume of the steam has increased so tremendously, it would be impractical to have only a single cylinder for the final expansion stage. Therefore, I have decided to use two cylinders running at the same pressure, to make a more manageably sized engine. In order to reduce these cylinder sizes further, all of the sundry uses for steam aside from expanding in the cylinders for propulsion (such as cylinder heating jackets, whistle, etc) will draw from this low-pressure reheated steam.
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