Design of Reciprocating Piston Expanders

Hi Dan,

It isn't just that you have counterweights, the counterweights must have the precise moment of inertia required to offset the forces generated by the reciprocating masses. In a typical engine this mass is calculated and the crankshaft is manufactured with counterweights that are a bit too heavy, then the crankshaft is precisely balanced in a dynamic (two plane) balancer. The typical counterweight will produce inertia equal to the mass of the rotating component added to the crankpin plus half the reciprocating; this either accomplished by adding precisely that much mass to the crankpins and then balancing the crank to zero or by using a balancer calibrated with a master crankshaft already precisely balanced to the same inertia.

Simply using an inline 3 crank won't work, you will need to add very dense metal to the counterweights sufficient to compensate for all the additional mass moving up and down the cylinder. This can be accomplished by adding Mallory metal (a tungsten alloy) to the counterweights....if you haven't made the added reciprocating mass so great that you can't add enough metal to the counterweights.

An inline 4 cylinder engine is typically inherently balanced for primary unbalance forces, meaning that the primary balance is always correct no matter the mass added to or subtracted from the crankpins. The secondary forces are not balanced and can only be compensated for by the use of balance shafts. An inline 6 is inherently balanced for primary and secondary forces. V-8s are not inherently balanced because changing the masses affects the balance, but when balanced to the correct masses they are fully compensated for both primary and secondary forces.

Even inherently balanced cranks usually have relatively accurately calculated counterweights, the counterweights might cancel themselves along the length of the crank but locally they cancel out bending forces applied to the crank by the reciprocating mass. This reduce bearing wear and crank fatigue.

Needless to say, this isn't the sort of thing you can do on a typical workshop bench; took me quite a while to figure out all the ins and outs on the job.

Hey Tim,

Yep, I've seen that patent, but I had to have no social life in order to compile 6000 odd steam related patents on disc. Harry Ricardo certainly had an on again, off again interest in steam engines and some interesting notions on engine balance as well. Have you see 2,103,389 issued to Allen C. Staley? At the time Staley was a Chrysler engineer working on early automotive air conditioning systems. He worked on early automotive gas turbines and supercharging before and during WW2. What makes the patent interesting is that he was an engineer working on the Doble Detroit, the Scott Newcomb, Stanley steamers and the Coats steamer. The valve in this patent suggests that maybe he had the idea in the back of his mind while working on steamers, it is opened by cylinder compression and cam closed. It has some interesting features that might make for an interesting steam engine admission valve.

Regards,

Ken



Edited 2 time(s). Last edit at 01/20/2015 09:44PM by frustrated.

I see Stanford has a copy of Engineer's digest vol 2; anyone near stanford?

Dan

Ken:

Where can I learn more about engine balance? Is there a book?

Dan

Hi Dan,

There is quite a bit of information regarding engine balance on the internet, it is generally of the practical "how to" variety with some theory tossed in. The books I have seen specifically on the topic are way, way too detailed and tedious for anyone who isn't interested in pure scholarship; engineers designing cranks certainly don't go into that kind of detail. About 12 years ago I wrote an article on the subject for the Bulletin, I'm sure it could stand a lot of editing but the information should be good; I'd say its a good place to start, anyhow

Balance 2003 PDF

Regards,

Ken

Thanks Ken!

Very interesting paper Ken. So if at all possible if i wanted to turn the engine into a steeple compound, ideally I would try to keep the combined weight of the two pistons and the connecting rod close to the weight of the original piston, or be prepared to add a whole lot of weight to the crankshaft.

It's possible that the LP piston ( bottom one ) could be made lighter than the one it replaces. It seems to me it would not need to be as long, because the two pistons guide each other. At least it would seem that way.

Dan



Edited 2 time(s). Last edit at 01/20/2015 11:57PM by dullfig.

Nope, that's not right. The bottom piston has to cover the exhaust ports or steam will vent into the crankase. So it has to be long.

Dan

dullfig Wrote:
-------------------------------------------------------
> I see Stanford has a copy of Engineer's digest vol
> 2; anyone near stanford?
>
> Dan

PS: There was also a US Coast Guard internal publication called "The Engineer's Digest" published in the 1940s, but it's not where this article is.

Tim: I'm not sure which periodical it is that they have. Trying to find out

Ken: I'm wondering why Doble designed his ultimax as a three cylinder, considering it is not inherently balanced

Dan

This is great information, thanks for sharing. today I feel like an ant looking at Everest. external combustion engines were made before, more recently, and new ones will be built. At least five startups in the decade reflect the solid fundamentals behind it. apart from one, others are stationary.

Notwithstanding the plod, steam lost to diesel once, wondering if supercritical pressures and higher temps can make it go mainstream again, if ever. guess Atkinson cycle diesel will still always be cheaper with die casting tech, but heaviest; miles cleaner. only a good experiment can settle it, one already claims equality to diesel efficiency.. so it's only a question of time, i hope, i hope

Rahul

Given the akinson is used in these gas hybrids:

Ford C-Max (front wheel drive / US market) hybrid & plug-in hybrid models
Ford Escape/Mercury Mariner/Mazda Tribute electric (front- and four-wheel drive) with a compression ratio of 12.4:1
Ford Fusion Hybrid/Mercury Milan Hybrid/Lincoln MKZ Hybrid electric (front-wheel drive) with a compression ratio of 12.3:1
Honda Accord Plug-in Hybrid[5]
Honda Accord Hybrid (front-wheel drive)
Hyundai Sonata Hybrid (front-wheel drive)
Infiniti M35h Hybrid (rear-wheel drive)
Kia Optima Hybrid (front-wheel drive) with a compression ratio of 13:1
Lexus CT 200h (front-wheel drive)
Lexus ES 300h (front-wheel drive)
Lexus GS 450h hybrid electric (rear-wheel drive) with a compression ratio of 13:1
Lexus HS 250h (front-wheel drive)
Lexus RX 450h hybrid electric (four-wheel drive)
Mazda 3 SkyActiv (front-wheel drive) with a 13:1 compression ratio (12:1 for North America)
Mazda 6 SkyActiv-G 2.5L (front-wheel drive) with a 14:1 compression ratio (13:1 for North America)
Mazda CX-5 (front- and all-wheel drive) with a 14:1 compression ratio (13:1 for North America)
Mercedes ML450 Hybrid (four-wheel drive) electric
Mercedes S400 Blue Hybrid (rear-wheel drive) electric
Toyota Camry Hybrid electric (front-wheel drive) with a compression ratio of 12.5:1
Toyota Highlander Hybrid (2011 and newer)[6]
Toyota Prius hybrid electric (front-wheel drive) with a (purely geometric) compression ratio of 13.0:1
Toyota Yaris Hybrid (front-wheel drive) with a compression ratio of 13.4:1
Toyota Auris Hybrid (front-wheel drive)
Toyota Tacoma V6 (beginning in 2015 for the 2016 model year)
You wonder how long it will be before they go to diesel akinson cycle engines in hybrids....maybe even a steam version of that engine.

I spend a lot of time reading 100+ year old engineering texts and trade publications. They are free (and I am cheap) and it is surprising how often we reinvent the wheel.

The modern "Akinson" cycle engines bear very little in common with the engine that Akinson developed and have nothing in common with his design goals.

The Akinson engine, like all engines of its time was large and slow moving, berift of the benefit of a crank case and lubricated by oil cups on bearings. Like many other bizzare engines of its time, its primary goal was to side step the Otto cycle patents. When Otto's patents expired, so did most of these engines.

Yes, Akinson was aware of the potential benefit of having the expansion stroke longer than the compression stroke. This was a secondary benefit. More important was the benefit of having a power stroke every crank revolution- this was important for large low specific output single cylinder engines. Of primary importance were Otto's patents. By the way, Akinson also experimented with engines that had the compression stroke longer than the expansion stroke. It was just a matter of readjusting the "crank" linkage.

I remember reading about a guy who modified a street going compact Ford car in the 1980's that was supposed to deliver 80 miles per gallon. He kept the intake valves open part way up the compression stroke, (and also used a heat exchanger that preheated the charge with exhaust gas). He was generally dismissed as a crack pot.

Don't get me wrong. There are advantages (and disadvantages) in closing the intake valve late. Is this an Akinson cycle engine? No- regardless of what the PR guys would have you believe.

What we call a "Diesel" engine has little in common with what Dr. Diesel invented. Diesel's primary concern was isobaric combustion, a concept that has been abandoned or is entirely lost on designers of modern "Diesel" engines. There have been a great many compression ignition engines designed, but these days few of them are Diesel engines.

Imagine a steam engine at the end of its power stroke. The piston returns driven by the fly wheel or another cylinder. The exhaust valve closes while the piston is part way on the return stroke. The exhaust steam trapped in the cylinder is compressed until the piston is nearly on center. Then the intake valve opens. Boiler pressure is applied and the cylinder pressure is constant until the cut off point- and this is critical (more later). The intake valve closes and steam trapped in the cylinder expands.

Diesel, like all of his contemporaries was familiar with indicator cards produced by steam engines. Diesel was trying to produce a similar card. Diesel used a long duration fuel injection to continue combustion and maintain relatively constant pressure until the piston had traveled some distance down the expansion stroke. The duraton of injection and therefore the peroid of isobaric combustion was equivalent to the period of a steam engine between the opening and cut off of the intake valve.

Now consider the card produced by spark ignition or modern "Diesel" engines. The piston ascends the cylinder compressing fuel and air (or air only in the case of a modern "Diesel" engine). The piston nears dead center and the spark ignites the charge or the fuel is injected. The cylinder pressure sky rockets (this is exactly Diesel was trying to avoid) and the piston returns on the expansion stroke.

Do modern "Akinson" or "Diesel" engines have their atributes? Yes- although the environmental chickens have definately come home to roost with regards the "Diesel" engines. Do modern "Akinson" or "Diesel" engines have anything in common with the design goals of their proported inventors? No. Are modern marketing people exploiting the name of venerable engineers of yesteryear to hawk their products? Definately!

Kerry



Edited 2 time(s). Last edit at 01/23/2015 11:48PM by kerry.

Hi Kerry

I agree with the sentiment of your last paragraph but would like to point out that modern direct injection compression ignition engines can have up to 5 injection events so that a progressive combustion takes pace rather than one large bang. Purpose is noise and emission reduction.

Brian

Catching up on these posts is interestimg. I think we could use a terminology page.

For example the difference between in indicator chart and a PV chart. Ken what become of the pages you started.

There are some basics of engine size that apply to any configuration. You need to use x amount of steam per unit time to make y hourse power. If two engines have equal expansion and inlet stean states they use equal amounts of steam to produce the same power at the same RPM . So in this case the ending volume of steam is the same.

That would mean the last stage of a compound would need to be equal in displacement to the non compound engine. The compound would be a larger engine and have little or no advantage. It would not have a good smothe torque operatoring power range. Using more cylinders in the single expansion engine can give you smother torque. Higher engine RPM (lower gearing) can get smother torque. A higher expansion throttle controled compound is at a disavantage. It has a nerrow efficient power range. The efficient power range is wide open down to the point of over expansion. (end of expansion pressure below exhaust pressure)

A compound would only have an efficiency advantage if the design parameters are radicaly different. Using a much higher pressure, never over expanding, and using a higher expansion ratio.

Andy

Andy,

If you over expand on a unaflow, whether compound or not, it quits running. No exhaust will come out. Air might even go in the exhaust ports. So, I imagine that the engine would start braking.

I am wondering if anyone knows exactly how a steam engine does engine braking?

Hope the world is finding you well, Andy,

Bill G.

Bill Gatlin Wrote:
-------------------------------------------------------
> I am wondering if anyone knows exactly how a steam
> engine does engine braking?
>
> Bill G.

Dear Bill, With our Stanleys, we do engine braking most of the time on long downhills where the brake lining has to be saved. Unless one knows all the pitfalls of engine braking, do not do it. Thomas Marshall of Delaware will not do it at all to his Stanleys. Engine braking would take a whole another thread to explain. I will try to fit it in when I have the time. Engine braking would be a good article to do for the the SACA Bulletin.

Bill,
Very simple. Steam car engines in forward gear have only their friction to help and it isn't anything usable.
You put the engine into reverse and it then acts like a compressor, sucking from the exhaust line and compressing against the closed throttle. Like running into a big sponge wall, it really works.
Problems are that the cylinders then get really hot, no oil is going into the cylinders and you can easily suck in a slug of water from the exhaust line and either blow out a cylinder head of bend a crosshead guide.
Watched two Stanleys get their engines wrecked this way. Dobles too along with a broken crankshaft once.
With the White, you stop at the top of the hill, shift into low gear, crack the throttle so the engine gets oil and safely trundle down the hill at 10 mph.
Jim

Jim Crank Wrote:
-------------------------------------------------------

> You put the engine into reverse and it then acts
> like a compressor, sucking from the exhaust line
> and compressing against the closed throttle. Like
> running into a big sponge wall, it really works.
> Problems are that the cylinders then get really
> hot, no oil is going into the cylinders and you
> can easily suck in a slug of water from the
> exhaust line and either blow out a cylinder head
> of bend a crosshead guide.

> Jim

Wow that is good to know!

On the Locomobiles, if I understand correctly, the muffler holds condensation - entry in to the side of the can and the exit is at the top. Then there is a feedwater preheater coil inside. I thought they did that because hot water would transfer heat better than exhaust steam. The muffler being full of water, if the engine is reversed it would pull the condensate right back. Or maybe these mufflers had a drain on them?

-Ron

Hi,

Well an I.C. engine brakes just by going to low or idling throttle. It must be inhaling a bit of air mixture, compressing it and putting the heat out the exhaust or coolant. More so with a Diesel engine.

So, for a Diesel engine; air would go into the cylinder on intake, be compressed and give up some heat to the cylinder walls on compression, expand and cool somewhat on expansion and be pushed out the exhaust on the exhaust stroke. This engine braking then is a combination of pumping losses and some heat loss to the cylinder walls.

Jim, do you think that the White having the throttle just cracked was providing just the right amount of steam for something similar? If the throttle was dead shut would the engine brake as much?

Best,

Bill G.

Bill,
No, it was to get oil into the cylinders. The friction in low gear did most of the braking. Dead shut made no difference.
There was no pumping loss because no one with any brains would even try to put a White into reverse going down hill. The drive shaft would be laying on the ground and you would be in real trouble
Jim.

Well, There has got to be some good way to get nice engine braking out of a steam engine. My compound design is more for trucks and it doesn't reverse due to the way it is laid out. I really hadn't thought of braking very much. Mountain roads need it.

Some way of sucking air in through a straw and blowing it out again might be an equivalent, but I would be hesitant to let air into a closed system.

Best,

Bill G.

Bill if you over expand simply going below pressure it is indeterminate what would happen with out exactly knowing the specifics. It could be insignificant not creating enough vacuume to create any significant inflow. Or catastrophic sucking condensate into the cylinder combined with possable condensate from over expansen and crunch.

In my engine simulations I have the cylinder pressure at least 5 psi above the external cylinder to insure some pressure difference to make outward flow. Usually 15 to 20 psi. I am not to conserned with that paremmeter till I get flow simulation working. Then I will be interested in actual numbers. There is the expansion tube exhaust we have talked about before. Of course we need flow for that to be effective.

Good point on over expansion being worse then just lowering efficiency.

Andy

Thanks Andy,

I am still wondering about various ways to effect engine braking. I don't think engine friction would be enough. Any ideas?

What do you think about Jerry's inlet valve in this last bulletin? I am thinking of possibly in a double acting poppet valve uniflow engine. It would save a lot of cam mechanisms.

Best Regards,

Bill G.

I'm also very interested in the valve design. The whole topic of steam pressure operation and steam springs should be a great area for new thought. Springs immersed in steam are an obvious weak point. I keep thinking that the Hemick/Crank "bashless" valve idea could be combined to give a non contact opening with a steam spring return.

The system has obviously been tested. I would be very interested in the details of that testing. My engine would run at a much higher rpm but with a variable pressure monotube boiler. I am interested in the simulation details as well to investigate higher rpm operation. The flash steam model engines have issues with their cam to valve interface at the 10,000 to 15,000 rpm they run.

Lohring Miller

Lohring,
In forward gear a steam expander has no compression. Putting it into reverse turns it into a potent compressor and it pulls from the exhaust line and pumps up against the closed throttle. It also generates a LOT of heat quickly, insulated cylinders remember, so oil has to go in or you will destroy the rings. If there is any water in the exhaust line, then bang goes the cylinder, cylinder heads or connecting rod. Seen two Stanleys have their engines destroyed this way, One blown off head actually bent the tie rod on a Mountain Wagon. One Doble broke the crankshaft and another one, due to owner ignorance, split the crankcase completely in half and I have photos of that one. In a car, huge power disk brakes, in a truck good luck, perhaps some water cooled brake or absorption unit like a dyno?

If you want to learn about springless valve gear, research the pneumatic valve systems used in Formula One cars, they can and have gone to 20,000 rpm which means 10,000 rpm on the camshafts.
What intrigued Ken and I to investigate using dry steam in place of the nitrogen they use. There seems to be a very good potential there. Ken refined my first concept into one that would be usable. Try it out in a simple test engine and let us know.
This fascination with model steam racing boats has no relationship to vehicle use. Scaling the clearances and taking the parts inertia and wild superheat into consideration makes them light years apart. There is an active model boat bunch here, fascinating to watch.
Jim

If there is an electrical system on the vehicle, employ regenerative braking? Recover the energy. If no 12volt system (this is a crazy idea) use a generator for braking like regenerative braking does, then take that across braking resistors (big ones) use the heat from the resistors to warm the combustion air and cool the resistors.

-Ron

Inlet Valve:

High speed, needing light weight. High superheat, needing cooling. Opens upward into the steam port, spring closes valve by pushing downward. Saturated steam from the Lamont tank at say 1,000 -1,500 psia and about 550 to 600 deg F.

This source of steam could supply the spring pressure to close the valve and also cool it. The small leakage around the valves piston goes to the inlet port. Valve spring eliminated. This could also work as the return spring for a piston valve configuration.

My piston valve (if I used one, inlet only) would be such, with cam operation and a Knight sleeve. The piston valve would open the inlet and the Knight sleeve, being lighter and faster, would close it. Again variable, or at least independent, advance and cutoff.

Best,

Bill G.

Jim Crank Wrote:
-------------------------------------------------------
> If you want to learn about springless valve gear,
> research the pneumatic valve systems used in
> Formula One cars, they can and have gone to 20,000
> rpm which means 10,000 rpm on the camshafts.
> What intrigued Ken and I to investigate using dry
> steam in place of the nitrogen they use. There
> seems to be a very good potential there. Ken
> refined my first concept into one that would be
> usable. Try it out in a simple test engine and let
> us know.
> This fascination with model steam racing boats has
> no relationship to vehicle use. Scaling the
> clearances and taking the parts inertia and wild
> superheat into consideration makes them light
> years apart. There is an active model boat bunch
> here, fascinating to watch.
> Jim

I have become a student of valve gear. Modern steam (is there such a thing?) seems to be stuck at cam operated poppet valves in high performance engines. An exception is the Gelbart engine with its bash valve held open by a magnet. There is a lot of interest in computer controlled and other variable valve actualion systems in IC engines. The Pattakon systems looked interesting. The simple variable lift system would make a good throttle for an engine. It would also work for a variable output feed pump. His desmodromic systems would allow variable cutoff as well as variable lift.

I'm also familiar with the formula one valve systems. A very simple spread sheet indicated that the pressure generated forces involved were a lot greater than the inertia forces, even at 10,000 rpm, for the Hemick/Crank valve. It just remains to design a variable closing delay to get a great camless valve mechanism. Jerry's system is one method, but it needs a high temperature spring and low pressure in the cylinder on the up stroke so there will be low pressure above the valve on opening. That's the opposite of the Hemick/Crank valve. At 10,000 rpm the delay needed is on the order of tenths of a milisecond. The valve in the article had a delay ten times as long. I'm not particularly interested in steam rate. The engines I'm interested in open their intake valve 7 degrees before TDC and have an open duration of 54 degrees. That's tough on the cam and lifter at 10,000+ rpm. It would be nice to duplicate this in a camless system.

Lohring Miller

another consideration of very fast and infinitly variable valve gear is one developed and tested by brilliant Hal Fuller when he was at Skinner.
He developed a hydraulic valve gear based upon diesel fuel injector technology that was extremely fast in lift and totally variable in admission, he made a two cylinder auxiliary steam engine while there and was told it worked extremely well.Its only problem is that without a small side pump to keep the valves in place when the engine was stopped, an easy problem to solve. I would think with very high hydraulic pressure to lift the poppet valve stems that stem lubrication would move up the stem and prevent steam leakage. Possibly Hal would car to comment on this.
GeorgeN

Bill Gatlin Wrote:
-------------------------------------------------------
> Inlet Valve:
>
> This source of steam could supply the spring
> pressure to close the valve and also cool it. The
> small leakage around the valves piston goes to the
> inlet port. Valve spring eliminated. This could
> also work as the return spring for a piston valve
> configuration.
>
> Bill G.

It's tough to design a steam operated valve that would close with the same pressure (steam inlet pressure) on both sides. That's why Jerry's valve needs a spring. The obvious way is to use a larger piston on the upper side of the valve actuating cylinder. However, you need to have low pressure on the bottom of the valve actuating piston on closing. This means a fairly leak resistant rod seal and a valving system to operate the valve actuating piston. You might as well run a completely mechanicat valve actuation mechanism. Cam operated poppet valves have been around a long time and are well proven. So far, none of the electrohydraulic systems can compete. I would think the problem would be even harder at superheated steam temperatures.

Lohring Miller

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File Name	File Size		Posted by	Date
Surface area and clearance % to bore and stroke.xls	333 KB	open | download	Caleb Ramsby	01/13/2015	Read message
XSteam_Excel_v2.6_US.xls	397 KB	open | download	Caleb Ramsby	01/14/2015	Read message
X_Steam_Tables.bas	153.6 KB	open | download	Caleb Ramsby	01/14/2015	Read message
Uniflow Engine Section Details.png	218.8 KB	open | download	lohring	01/19/2015	Read message