Steam rate required for the Surrey

Please lend your expertise and tell me if I am on the right track. I am trying to size a boiler for my 1959 Surrey which is a full scale replica of a 1903 Olds. It currently has an 8 hp IC engine in and I am going to convert the vehicle to steam.

So here is the question. What steam rate do I need to go 15 mph on the flat. Driving over that speed with the suspension, steering and brakes is best left to a younger man as they have more time to heal. Here is how I came up with my numbers. The results are 28 lbs/hr. Sound OK?

All help/laughs appreciated, Roger

Inputs to calculate the required steam rate
Speed 15 mph
Vehicle weight 760 lb
Passengers 330 lb
mu 0.020
Cd 0.7
Density of air 0.003 slug/cubic ft
Frontal area 25.0 sq-ft
Assumed engine steam rate 20 lbs/hp-hr

Intermediate calculations
Speed 22.0 ft/sec
Total weight 1090 lb
Frictional resistance 21.8 lb
Wind resistance 13.4 lb

HP requirements
Rolling friction 0.87 hp
Wind resistance 0.54 hp
Total to-the-road hp 1.41 hp
Theoretical HP required 1.41 hp

Steam required 28 lbs/hr

The steam rate/hp is likely low; if this is a double simple or similar I'd expect at least 30lbs/hp-hr.

You can live w/ a smaller boiler if the boiler has a tank to permit drawing more steam for acceleration,
etc; you'll need to manage the use by watching the pressure drop.

- Bart

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Bart Smaalders [smaalders.net]

Bart, I am envisioning an external bash valve single acting engine with uniflow and auxiliary exhaust and a torque converter (like they use in go-karts). The best I have ever gotten out of Katie Ann Too's engine (double acting/slide valve) was indeed 30 lbs/hp-hr as you suggest. And that was with 600 F steam. With saturated steam, it was 60 lbs/hp-hr.

Roger

Roger,

If you solved this question on the basis of an assumed steam rate, your answer will have no more fidelity than assuming the answer at the outset. Steam rate depends upon pressure, temperature, clearance, cutoff, engine friction, pump work and exhaust conditions. Actually, there is insufficient information to get an acceptable answer.

However, you can get to steam demand by assuming engine efficiency and enthalpy change in the generator: divide horsepower by engine efficiency and enthalphy change. Depending upon engine efficiency I get a minimum rate of 16 lb/hr and a maximum of 24 lb/hr.

No one is laughing here, This is serious stuff. Never the less I do smile when air density is given on the basis of slugs. This is the old Gravitational system with English units. I prefer the engineering system where density is pounds/cubic foot.

Jerry

Thanks Jerry. Steam demand is a much better way to put it.
Roger

Roger
Decided on the engine you are going to use to achieve the HP required.
Take the cylinder volume X the RPM X 60 and you will have total Cu feet per Hr. Go to your super heated steam tables for the pressure and temperature you intend to use. Should be at least 200 degrees over saturated, and convert it Lb/Hr. add 25% for maximum boiler output. A Lb of steam is a Lb of water.
Don’t start subtracting cut off and all the other stuff you will have enough lose with ring blow by and
Packing glands.
By the way the hydraulic cylinder shafting is nice stuff for the piston rods and valve rod if you can get it in short lengths. Ground 440C SS is also nice stuff. I use to use a lot of monell but the price now is way up there.
Rolly

I would look at an antique Locomobile or the recent Modelworks Likamobile replica - about the same size as and speed as your project - then aim for similar steam output. That's probably as close as you'll get.

Mike

1.4 Gross Horsepower for an 1100 pound vehicle is a bit too minimal I would think. Also, as others indicate, 20 pounds of steam per horsepower-hour is way too optimistic. Mike Clark has the right answer, copy what works if available.

Hey Rolly,
Sounds like a good approach to starting on an engine once I get the hp requirement nailed down. Thanks.

Hey Mike,
I have taken a cursory look at the Likamobile and can talk with Harry Hibbler for more details.

Fred, which item do you think is too optimistic. The .9 hp for friction or .5 for drag? The numbers do seem low to me but I can't figure out where I might have gone wrong. I assumed a Cd of .7 and a coefficient of friction of .02. Also, what do you think the number should be? It is pretty easy to imagine that the steam rate is too optimistic but I do need to nail down the hp requirement.

Roger

Well, what happens on a 3% grade? I think your hp requirements more than double.... You have both immediate and average hp requirements.... the engine has to be able to handle the immediate power needs; the boiler needs to be able to do the same, but if you have a drum type boiler you can overdraw for a little while so your heating surface & fire need to match the average, not peak, power requirements. The big challenge in driving a rig w/ more engine than boiler is not using too much steam and dropping the pressure too far.

- Bart

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Bart Smaalders [smaalders.net]

Bart--3% grade? You think I live in Florida or something? This is all jumping ahead of the HP requirement on the flat question, but I have a 10% grade to climb here and fortunately I don't need to go up it fast as it is not on a busy road (3 mph is fine). So I realize I will have to address that issue pretty soon.

Roger

To all,

We finally got a warm enough day in GA that I could take the Surrey out and measure the power requirement by measuring the time it takes to coast from 17.5 mph to 12.5 mph. The results--the force on the car was 31 lbf. I had calculated 35 so was pleasantly surprised. So for now I have a solid piece of information--I need about 1.5 HP to go 15 on the flat. Now to the next step. Hill climbing.

Roger

Seeing that reference to slugs brought back memories of one professor with a rather warped sense of humor, that wanted answers converted into units such as slug-furlongs per fortnight. Ah, the English system of units! Metric is boring!

Tom

I had an incident a few years ago where they were putting some really big cutters into an obscure CNC machine and the German builders had put some placards on the machine specifying all sorts of limits as to moments of inertia for the tools...no one had seen stuff like that before. The tooling engineers spent a couple of days on the phone and didn't get any answers, so they copied all the data down and dumped it on my work bench on the theory that the balance guy deals with more weird measurements than anyone else. After a couple hours I realized the problem was that the machine was in metric and the tools were in english and they had just used the straight "conversion" of 2.2 pounds per kilogram---which usually works for most purposes except when inertia is involved and you need actual mass. This sort of thing is a lot easier to spot when you aren't constantly converting EVERY single stinking variable. A quick conversion into slugs, a bit of algebra to cancel out all the different units and the answer was pretty simple....we could have just dropped the tool into the machine and I can't even imagine a tool that can fit in the holder that would exceed those limits, which sort of begged the question why they were posted on such an obvious placard. I did want to call my old high school physics teacher up and thank him, obviously he was more alert to this sort of thing back when he taught us back in the 70s than the professors were when the engineers went to the university in the 90s....

Regards,

Ken

I've been reading your posts on your conversion, and I may be able to supply some info since I own a Modelworks Likamobile that I built and completed 2010. There was a steep learning curve on the car from the original Locomobile. The car came with the Model Works engine which was suppose to be a copy of the Mason/Locomobile engine. But it had its problems with the redesign. The engine was removed, modified and just sold. It was replaced by a 1899 mason engine that I rebuilt and installed.The Mason engine was first used in the Locomobile from 1899 to 1900. Then the Locomobile company designed there own engine which was a copy of the mason engine. The car has been running with that engine for about a year (not much time on it), I just purchased another engine, its a 1901 mason engine with improved cross head guides (latter design). This engine is not in the car yet, it will be rebuilt and be installed this spring. Then the 1899 engine will be sold. What was found in driving the car was 8 Hp had its limits on hills. The boiler was a Model Works design, which is a water tube type with a 12 volt oil type burner the kind used in steam cleaning equipment. The Locomobile used a fire-tube type with a vapor burner. The control system used for the Likamobile is a modern type which uses a electronic control circuit board. This makes things very automatic so its easier to drive. The burner has a 1.75 g/hr nozzle in it, at times I will have to wait for the pressure to come back up when climbing a hill. I will be changing the nozzle to a 2.0 g/hr. The boiler is safety for 250 psi and the operating pressure is at 245 psi. I have the technical books on the original Locomobile and use them for reference when making any changes. What is occurring is the Likamobile is becoming a Likamobile/Locomobile.

Nice looking Likamobile, thank you for sharing your experience with the engines.

Thanks for the info on the Likamobile. I see that it has the same shape fenders as the Surrey I have.
Roger

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