Triple expansion to I6?

[jazz256]

Hello everyone, My name is James Jones and I am trying to build a steam car. For the past year, I have been researching and reading about steam engines, boilers and other systems. In my quest to build my car, I have read about the Doble, White, Stanley, Baker and various other steam cars (and locomotives.) One thing that intrigued me was that the Doble had a four cylinder steam engine, which were two compound steam engines on a common crankshaft. I also read that triple expansion steam engines were efficient engines for their configuration. My question is, is it possible to mate two triple expansion steam engines together on a common crank? I seen the possibilities of the engine being naturally balanced and the engine being efficient, especially if I use a 15%-25% cutoff on both the high pressure cylinders.

 

[RonGinger]

I think triple expansion is only useful when you can work into a condenser to create a vacuum. They were used on boats where the water made a great cooler. I do not believe anyone every made a triple loco and even compound locos were rare. Your idea of two engines sounds like it might be better to make one engine of larger bore to gain more power. Making two engines, besides being a lot more work, would have more friction and losses to surface area.

 

[Mechanicboy]

The single compound or triple expansion steam engine can not self start who is neccesary in the car and make more smoother running with double compound or triple expansion steam engine. In Doble car is the double compound steam engine used. The Stanley steam car had not compound or triple steam expansion steam engine, only 2 cylinder double acting steam engine. The steam car has radiator as condenser to create vacuum in low pressure cylinder and the condensed water is returned to boiler for long duration with less lost of water. In marine compound or triple expansion steam engine is starting with the simpling valve who is sending the steam pressure to middle pressure- or low pressure cylinder to start up steam engine. Cylinder volume in Stanley car was not large, 4" bore and 5" stroke is powerful enough!

 

[Charles Lamont]

One of factors affecting efficiency is the size of the cylinders. Small cylinders
have more surface area in relation to their volume than large ones. This has two consequences, the relatively larger external surface are will lose more heat, and the internal surface, heated by the incoming steam, will then give up more heat to the outgoing exhaust, so thermodynamically your 6-cyl is likely to be less efficient than a triple of the same overal volume.

Mechanical losses would also be almost twice as great. Balance of a 3-cylinder
engine can be pretty good, although there is a 'rocking couple'.

I have never heard of a triple expansion road vehicle, let alone a successful one (though I am not saying there was no such thing).
Compounds tended to be used for road traction engines (road locomotives) mainly because they used slide or piston valves with the limitations of their valve gear, and superheaters were regarded as an over-complication. One of the most successful more modern designs of road steamer were the Sentinel waggons, which had simple expansion engines with poppet valves and sliding camshafts for reversing and cut-off variation and using superheated steam. In particular, the last model, the S-type, had a 4-cylinder single-acting engine, and in 1934 this was a steam lorry comfortably capable of 40 mph (and, reputedly, getting on for 60).

 

[jazz256]

So, its safe to say don't try to mate two triple expansion engines together and put it into a car?

 

[jazz256]

One of factors affecting efficiency is the size of the cylinders. Small cylinders
have more surface area in relation to their volume than large ones. This has two consequences, the relatively larger external surface are will lose more heat, and the internal surface, heated by the incoming steam, will then give up more heat to the outgoing exhaust, so thermodynamically your 6-cyl is likely to be less efficient than a triple of the same overal volume.

Mechanical losses would also be almost twice as great. Balance of a 3-cylinder
engine can be pretty good, although there is a 'rocking couple'.

I have never heard of a triple expansion road vehicle, let alone a successful one (though I am not saying there was no such thing).
Compounds tended to be used for road traction engines (road locomotives) mainly because they used slide or piston valves with the limitations of their valve gear, and superheaters were regarded as an over-complication. One of the most successful more modern designs of road steamer were the Sentinel waggons, which had simple expansion engines with poppet valves and sliding camshafts for reversing and cut-off variation and using superheated steam. In particular, the last model, the S-type, had a 4-cylinder single-acting engine, and in 1934 this was a steam lorry comfortably capable of 40 mph (and, reputedly, getting on for 60).

That was one of my concerns about a regular triple expansion engine, the rocking couple at higher rpm. I would hate to build this engine, use it, then find out the engine shook its self apart. The only way to offset that would be to use counterbalancing shafts; which would add more complexity and cost to the engine.

As far as cylinder size, I wanted my higher pressure cylinder bore to be 1 1/8; middle cylinder 2 1/4, and low pressure 4 1/2. I have no problem with using a simpling valve to start the engine. I just like to be different and try something new. My first car was Volvo s80 t6; twin turbo inline 6. My dad had a 2008 jaguar xj with a v8. Comparing the two, by far, that Volvo and its engine was outstanding in its performance and I was instantly hooked.

In my studies about the Doble car and its engine, I was amazed but perplexed. The four cylinder concept was outstanding, but then, I thought to myself, why not use three cylinders for greater efficiency? Why not make a small inline 6 and stuff it in the car? It seems that it would be powerful using modern materials and design...

 

[Mechanicboy]

. This has two consequences, the relatively larger external surface are will lose more heat, and the internal surface, heated by the incoming steam, will then give up more heat to the outgoing exhaust, so thermodynamically your 6-cyl is likely to be less efficient than a triple of the same overal volume.

Jazz256..
You need a powerful boiler who is too large for a car..

The Doble steam car had a single tube "flash" type 575.74 feet,
Coils of 22 inch diameter stacked 13 inches tall.
Operating pressure 750 lb/in^2
Operating temperature 750 deg. F.
Cold start 30 seconds. And four cylinder, double acting, balanced compound. Two high pressure and two low pressure pistons. Displacement 381.16 cuin. Bore X Stroke High pressure 2.875 x 5.00 low pressure 4.000 x 5.00.

No triple expansion steam engine in steam car.

 

[jazz256]

In that case, would a 2 inch bore, 4.5 inch stroke, single acting, inline 6 steam engine work? I will have the benefit of high rpm, balance, and cut off for steam expansion the cylinder. I've been up all night thinking about this single acting I6. As far as steam generator space is concerned, I designed the car to be fair massive. The wheelbase by its self is 132.75 inches and that is on the small side of things.

 

[Mechanicboy]

In that case, would a 2 inch bore, 4.5 inch stroke, single acting, inline 6 steam engine work? I will have the benefit of high rpm, balance, and cut off for steam expansion the cylinder. I've been up all night thinking about this single acting I6.

6 cyl steam engine + high revolution= more steam consumption = larger boiler = uneconomical to run due more fuel to produce enough heat to boil water.

Steam engine produce more torque than combustion engine from zero revolution. In case the steam engine is loaded, it will produce more torque in lower revolution. More revolution means more amount of steam and pressure ---> large boiler who is to large in the car.

The steam engine in a Stanley turns at quite a slow rate as compared to an internal combustion engine. There is no transmission on a Stanley as the gear on the steam engine crankshaft is directly engaged with the ring gear of the differential. There doesn't need to be a transmission as the engine can be stopped when the car is stopped ~ its just like a steam locomotive. The speed a Stanley engine turns when traveling at a given speed ~ lets say 30 miles per hour ~ is actually more a function of the car's tire diameter than anything else. For a 1918 Model 735 the tires are 36 inches in diameter giving a circumference of 113.112". With 5,280 feet in a mile, that equates to 63,360 inches per mile and thus means a Stanley wheel turns 560.153 times per mile traveled. Thus, if the Model 735 were traveling along at 30 MPH, each wheel makes 16,804.582 revolutions per hour, or is turning at a rate of 280.08 revolutions per minute! The gearing ratio between the differential gear and the engine gear is 40 teeth on the engine gear and 60 teeth on the differential gear giving a 1.5:1 ratio. Thus the engine must turn at a slightly higher rate or 420.1 RPM when the car is traveling at 30 MPH. To look at it slightly differently, a Stanley car traveling at 30 miles per hour has the engine turning over at a slower speed (420 RPM) than an internal combustion engine idles at when at rest (typically 650 RPM)! The steam engine's crankshaft is turning 840 revolutions per mile traveled (the wheels rotate 560.153 times per mile traveled and the engine crankshaft turns 1-1/2 times for every wheel rotation). With that slow speed there's not much opportunity for wear of engine parts.

To produce less steam and enough power to drive a car: 2 cylinder double acting steam engine or double compound steam engine for better economical running with condenser added in car + low revolution from steam engine in correct gear ratio to rotate wheel in average speed in normal traffic/land of road. The Stanley steam racing car ran up to 120 miles/hour in 1909 with 2 cylinder double acting steam engine, also uneccesary to have multiple cylindre steam engine or high revolution from steam engine.

 

[kvom]

The Stanley engine had the capacity to generate a quite enormous HP output. However the water/fuel capacity precluded operating at anywhere near its potential.

 

[lohring]

Answers to a lot of your questions can be found in the Steam Automobile Club of America forum. The early issues of their quarterly, also available on line, has articles by people who actually built steam cars.

Lohring Miller

 

[Mechanicboy]

Forgotten to write in early post.. Do not have too big steam engine is to be believed that it performs best when you do not take the size of the boiler. Horsepower is determined by the boiler that produces steam flow / pressure steam engine will provide the best effect. Thus it is not the steam engine that determines horsepower. Too little steam boiler -> steam engine loses power.

 

[jazz256]

I also have to take into account engine balance so the engine will not shake its self apart.

 

[Charles Lamont]

I also have to take into account engine balance so the engine will not shake its self apart.

What rpm are you expecting to run this thing at? (I think you are worrying far too much about balance). Mechanicboy seems to be confusing engine capacity with number of cylinders.

If you are thinking of a single-acting engine I would go closer to square. The Sentinel S4 engine was 5.5" bore x 6" stroke, and was happy up to about 1500rpm, producing 124 bhp at 800rpm.

I would agree with looking carefully at other people's past work, and not going for much in the way of novelty. You are unlikely to be a significantly better engineer than all your many predecessors.

 

[jazz256]

I was also looking at Jay Carter's bash valve steam engine with the 5% cut off. Supposedly, it is hailed as one of the most efficient steam engines ever.

 

[jazz256]

Better yet, what engine you think will find in this?

 

[MichaelWilliams]

The ideal reciprocating engine for a high performance steam car would be a variable configuration engine with several identical cylinders .

Take a simple example of an engine with three identical cylinders . This can be run as all cylinders high pressure or one cylinder high pressure exhausting into two low pressure cylinders as a compound .

Self starting with maximum torque at lower speeds . Maximum economy at higher speeds .

More cylinders give more combinations . Five or six cylinders is the sensible limit for a practical design .

 

[jazz256]

So a inline six, with all the being 2" and the stroke 4 1/2" with a 5% percent cut off will work? To try and boost the efficiency some keep temps around 500 degrees F and the pressure high, 1000 to 2500 psi? And I will still have the power needed to achieve my goal. I am also running a condenser too.

 

[lohring]

Another resource for all the things steam people have tried is Tom Kimmel's steam museum. It will take several days to look through the various papers on his web site. Chuk Williams converted an old Force 3 cylinder outboard engine to steam for his Bonneville record attempt. Others have converted various Mercury outboards. To get an idea of what the engine for a 150 mph streamliner looks like, see below.

Lohring Miller

 

[MichaelWilliams]

There is no advantage in using steam with a pressure higher than a few hundred psi and with moderate superheat temperature in a piston engine intended for a practical car .