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Experimental engine

Posted by mike t 
Experimental engine
May 22, 2015 11:13PM
Hi, I have been building an experimental engine on which the valve timing and configurations can be easily changed. Initial testing is to be done with compressed air. The engine is mounted on a dynomometer and the rpm, torque, supply pressure and flow rate are recorded. The load on the dyno can be varied by altering the field current and a series of switchable 50 W halogen bulbs form a load dump. The data is to be recorded on an Arduino based datalogger then put on a spreadsheet for analysis. The engine itself displaces 30 cc and is single acting, I have not tryed to dress it up as it is purely for collecting data on engine efficiency. Care has been taken with the internal tollerances to ensure consistant results. I have primarily used poppet valves for inlet and exhaust plus an optional uniflow exhaust. The following things can be changed: 1. inlet timing via cam keyed to crank, + or - 5 deg, fixed duration, 2.poppet exhaust timing via cam keyed to crank, 3.uniflow exhaust timing via shims on cylinder. 4.can use poppet exhaust or uniflow exhaust or both, 5.compression ratio via shims on head gasket, 6.supply pressure. 7. valve configuration, there are currently 4 interchangeable heads with different valve arrangements, I have plans for two more including a piston valve head to set a benchmark. The best performing arrangements will then be tested on steam.
Regards Mike T.


Re: Experimental engine
May 22, 2015 11:31PM
Some more pics of the engine, I am getting some spurious readings on the Tachometer, will have to sort that out. Also testing the effect of exhaust length.


Re: Experimental engine
May 23, 2015 12:43PM
That is some really nice machine work on your parts. I have just gotten into the Arduino micro controllers, it appears you can actually write code, very impressive. Your probably getting some transient feedback on your tach pickup. I use a capacitive pick up with an aluminum flag, its rated to 5000hz.

Jeremy
Re: Experimental engine
May 23, 2015 01:06PM
Here are some pictures of the capacitive proximity sensor im using. It provides a very clean signal and in addition to a tach its used to trigger my injection valve.


Re: Experimental engine
May 24, 2015 01:17AM
Hi, found a program error was causing the wrong tacho reading, approached it from a different angle and now it is all good, confirmed by a non contact tacho. The sensor I am using is optical. I guess hall effect may be more reliable an enviornment where heat and oil may be found. also replaced the torque measuring load cell with a smaller rated one for better sensitivity, yet to be calibrated.
Re: Experimental engine
May 24, 2015 10:25AM
We've had experience with several rpm sensors. Our inertial dyno used a magnetic reed that came with the Performance Trends data logger. It got eratic at high rpm. The optical sensor we tried was worse. We used Hall effect sensors on several boat projects and they worked more reliabily under worse conditions. The only problem we had was sensing rpm near the magnetic field and brush noise on our electric hydro. We moved the sensor to the gear box and solved the problem.

How are you measuring power? Is your electric motor acting as a brake? What do you load it with?

Lohring Miller
Re: Experimental engine
May 24, 2015 06:55PM
Hello all:

I remain a fan of the uniflow engine.

The question here is, has anyone tried a "hybrid" version of a pure uniflow, with a conventional (but separate--NO counterflow allowed here!) exhaust valve in the head, supplementing the uniflow ports.

This would supplement the uniflow exhaust on the upstroke phase of the cycle and reduce or remove the recompression that inevitably occurs. Question is, how badly does this degrade the "ideal" version of the uniflow, and does the elimination of most (or all) of the work input into the recompression that inevitably results from a classic uniflow layout contribute enough to be a worthwhile advantage.

I would encourage mike t to explore this particular combination of design details with an eye toward a possible (but simple!) design detail that may be worth pursuing. The trade-offs between so-called "efficiency" and "power-to-size" may be worthwhile here and the simplicity of including this design detail may be worthwhile.

Just another FWIW.

Bill



Edited 1 time(s). Last edit at 05/24/2015 06:58PM by Bill Hinote.
Re: Experimental engine
May 24, 2015 07:34PM
Lohring, I'am sensing power with the automotive alternator, the housing of which is free to rotate in bearings coaxial with the shaft, a load cell is connected to an arm. I can increase the load by increasing the field current up to the maximum rated output of the alternator (which is not really big enough). The power from the alternator is dumped into some halogen bulbs which can be individually switched on to increase the load. A 200 watt alternator would have been more suitable however I used what I had at hand.
Bill, you will notice that three of the heads have a seperate exhaust valve which when used in conjunction with the uniflow exhaust becomes your auxillary exhaust. I practice it would be nice to thermally isolate the aux exhaust port from the inlet to reduce heat loss, I have some ideas for this. I believe that a pure uniflow while thermally efficient, will produce less power for a given displacement due to recompression than an engine without recompression ( probably with an auxillary exhaust valve) .This will mean that the internal friction losses will take a greater percentage of the power produced, thereby reducing the advantage of the uniflow. It is my aim with this test engine to determine (at least in this particular engine) if the theoretical benefit of a uniflow is real or not. Similarly I will be able to determine the effect of compression ratio. Another feature I wish to test is the power loss due to valve operating forces. Some of the valves have the pressure trying to open them, and some have to be opened against the pressure, I believe the valve operating mechanisim robs the engine of a considerable portion of its power.
Regards Mike T.
Re: Experimental engine
May 24, 2015 07:59PM
Hello again mike t:

Your reply perfectly matches my concept here: The tradeoff is between so-called "efficiency" (which is power produced per lb/hr of steam) and "power density" (which is power produced per lb. or per unit of displacement). These parameters need to be compared to create the best possible power unit.

I have never seen an evaluation of these parameters--much less a possible result of the optimization!

Not simple.

B.
Re: Experimental engine
May 24, 2015 10:55PM
In determining the advantage of a uniflow the should be running the same cycle. That is the counter flow should have the same compression. Ideally compression to near inlet pressure.

In calculating the engine efficiency flow and heat transfer is not considered.

The cycle program I use figures steam at cutoff as a mixture of residual steam and inlet steam. At Vcutoff having 1 unit mass. One pound for example. The unit mass being a mixture of mr and mi. The total being 1 unit mass. I wrote various cycle function taking different parameters. They all figure the residue mass at TDC. We can use the compression pressure, compression ratio, exhaust close.

No mater the cycle parameters we need the compressed steam mass and state. The residual state is calculated from the residual steam state in the cylinder at exhaust close And compressed (or not) into the clearance volume isentropicly. The state at cutoff is then figured by summing the enthalpy. Hr × mr + Hi × mi.

The Ideal Ranking clearance compression cycle is calculated simular to the standard Rankin cycle. Constant pressure admission. Isentropic expansion, isenthalpy drop to exhaust pressure, constant pressure exhaust, and isentropicly compression. There is controversy as to the residual steam state on dropping to exhaust pressure. My old books described the drop as a free expansion. Which is a constant enthalpy process. Some say the residual steam state should be calculated ad an Isentropic process. I changed my program to do a specified combonation. 0 to 1. 0 being totally conatant enthalpy 1 being totally isentropic. 0.5 being equal parts. I question in the case of isentropic pressure drop what work is produced. None the I provided the ability to use either.

The ideal engine cycle does not include flow or heat transfer.

In theory the compression work is returned on expansion. The calculated result of a full expansion, compression cycle is equal to the work of the admitted steam part. The efficiency is the same as the zero clearance full expansion cycle.

That is efficiency is at max having full expansion and compression to inlet pressure. The output power is proportional to the steam admotted.

To really test of uniflow has some efficiency advantage one would need to have identical cycles. Not really possible as a uniflow exhaust is part of the power stroke.

The best is two enginea having identical clearance running the same inlet steam state and having same expansion and exhaust pressure. The counter flow engine should have separate exhaust and inlet paths.

Andy
Re: Experimental engine
May 25, 2015 04:29AM
Hi Andy, I can test this engine as a uniflow or poppet exhaust in head or both. All these configurations have the same compression ratio, and with the poppet exhaust cam timed to suit, all can have the same expansion. A second engine may have slight differences in cam profile or port flow or internal friction etc. My engine removes any unknown variables and should give comparitive results. Whether the results I get will apply to a larger displacement engine is another matter. Also the configuration that shows the best efficiency on compressed air may not be the most efficient on steam, however I hope they will be similar and that I can eliminate the worst performing arrangements, thereby reducing the number of steam tests I need to do. There are 84 different test runs to do with the parts I currently have built, each additional head will add 24 more test runs.
regards Mike T.
Re: Experimental engine
May 25, 2015 11:00AM
Mike, it sounds like you have an excellent setup. My experience is with an inertial dyno, but I plan to test my 23 cc steam engine with a water brake because I have an old kart water brake. You are much farther along. Please keep us up to date on your testing. I am especially interested in your steam results. Are you planning higher pressures?

Lohring Miller
Re: Experimental engine
May 25, 2015 05:36PM
Hi Lohring, I do intend high steam pressure tests later on, will have to do a couple of mods to the engine though, some decent head bolts for a start, and a heat resistant crown on the piston, which is alluminium, I hope the alloy heads will survive short runs. I intend runs at 3 different pressures so I can plot a projected curve of the output and efficiency. I expect each engine configuration will have a different sweet spot where it performs best, from this I hope to be able to predict the best arrangement for an engine of 10 x larger displacement. I know I should have made the test engine larger but it was sized to utilize the materials at hand. What I have not been able to come up with is a suitable method of measuring steam flow as the flow sensor in use on this set up has a plastic rotor and housing. A test boiler will also be required as the monotube boiler I currently have has too small a volume to easily stabilize the steam pressure as required for conducting accurate tests. A water brake sounds like a good idea as it should not be as power limited as the alternator I'm using. The alternator may have to be geared up to increase its ability to absorb the power produced with higher steam pressures, I'm guessing it should be safe to 16,000 rpm (the alternator).
Regards Mike T.
Re: Experimental engine
May 25, 2015 08:40PM
Mike

Measuring steam flow is tricky business. You will find it much easier to measure the water flow into the boiler.

Kerry
Re: Experimental engine
May 25, 2015 10:13PM
I hoped that someone would come up with a good idea, thanks Kerry.
Re: Experimental engine
May 25, 2015 11:36PM
kerry Wrote:
-------------------------------------------------------
> Mike
>
> Measuring steam flow is tricky business. You will
> find it much easier to measure the water flow into
> the boiler.
Hello:

I agree with Kerry here--but the caveat is that transients and inertial effects in the generating system can produce errors.

The only thing I can think of is to allow the system to dynamically stabilize at a delivery rate that is equivalent to the anticipated rate to the test engine. There could be substantial deviations and it may be difficult to ID them so measured results could be put into doubt as a result.

B.
Re: Experimental engine
May 26, 2015 12:18PM
There are two long established ways to measure the water rate of any steam engine.
1) Put a calibrated flowmeter on the inlet to the steam generator.
2) Collect and weigh the condensate coming from the condenser.
Both assume the leaks are eliminated and you run for a reasonable length of time to average out the readings, thus taking care of transients.
Jim
Re: Experimental engine
May 26, 2015 05:22PM
You might consider coating the aluminum piston. Check out Tech Line Coatings.
[www.techlinecoatings.com]

Lohring Miller
Re: Experimental engine
May 26, 2015 07:58PM
I think water rate is incidental, how does one go about measuring efficiency of the of the expander.
Re: Experimental engine
May 26, 2015 09:11PM
I can't think of a better way to measure the efficiency of the expander itself than by measuring water rate, assuming we have basic but proper instrumentation set up on the engine. Once we know inlet temperature and pressure, we know how much power (BTU) went into the engine. Divide the power developed by the admission power and we know how efficient the expander is. Since this is pure input divided by output it takes all the hotel loads and incidental losses into account in one swell foop. Sometimes the old ways are darn good.

Calculating overall system efficiency by measuring water rate would be much more difficult, especially if assuming any kind of thermal regeneration. Fortunately, no one building other types of engines worries about such nonsense. They determine the BTU per pound of fuel and divide power output by the total energy content of the fuel consumed.

Regards,

Ken
Re: Experimental engine
May 27, 2015 12:46PM
Ken spelled it out correctly.
The water rate is the singular most important measurement one makes when developing any steam engine.
It and it alone will tell you the size of the steam generator, feed pump and condenser needed. Plus then the amount of heat input needed to maintain the pressure and temperature to provide that horsepower.
So, you accurately measure the water flow rate, fuel consumption and horsepower output continuously over a reasonable time span.
Anything less is just playing around.
Jim
Re: Experimental engine
May 27, 2015 04:56PM
Quote
Jim
So, you accurately measure the water flow rate, fuel consumption and horsepower output continuously over a reasonable time span.

Sounds simple enough, however I would have to have a flow meter that can at least withstand 1500psi. Fuel consumption would be easy for me to measure. I also have a DC alternator and could measure power using an amp meter its rated to 100 amps continuous.
Re: Experimental engine
May 27, 2015 05:10PM
Jeremy
I’ve done this many times to test my boilers.
I measure the water cold before it goes into the boiler as well as the fuel.
No big deal.
Rolly
Re: Experimental engine
May 27, 2015 05:23PM
On my setup the feed pump uses a regulator valve which dumps excess water to the jet condenser. The only way I can trust the water flow measure is as the feed pump outputs water that to go's into the engine and the pressure of this water is quite high.

edit- the water under pressure is not heated as it leaves the feed pump.-



Edited 1 time(s). Last edit at 05/27/2015 05:37PM by Jeremy Holmes.
Re: Experimental engine
May 27, 2015 07:16PM
Hi Jeremy,

You really want to do steady state tests, this makes water rate calculations easy since you don't have to sweat measuring changes in pumping rate.. Simply measure the water in the feed tank before and after the run, do not recycle feed to the tank as that is only necessary when measuring system rather than expander efficiency. You can measure the water with a graduated dipstick, gage glass or stick the tank on a scale. The two former methods require finding the weight based on change in tank level, the latter is a direct measurement.

Regards,

Ken
Re: Experimental engine
May 27, 2015 07:24PM
Hi, I have the same problem Jeremy, in that I bleed off excess water from the feed pump before the boiler, so it seems that an efficient condensor and measuring the condensate over a precise time span when running at a steady setting is the best method open to me. I had visions of an internally tapered sight glass containing a ball mounted vertically to indicate the steam flow rate, however it would be limited to lower pressures and temps. I have been looking at the pistons used in big diesel trucks, many are using steel pistons or a composite of steel crowns and alloy skirts, my intention was to rivet a thin stainless crown to the current piston. Thanks for all your comments, Mike T.
Re: Experimental engine
May 28, 2015 03:22PM
I found this site flow meters
Im thinking some where around 5 gpm at the high end.
Re: Experimental engine
June 09, 2015 01:53AM
Hi there, time for an update. Got the sensors all calibrated, then had lots of fun getting the sensors to read when the engine was running. The main culprit was vibration and operating the flow meter outside its recommended range. The load cell would not hold its calibration, may be drifting with temperature changes. I am currently reading the torque from a spring scale. Next problem, the alternator is not capable of providing sufficient load to restrain the engine from over-revving when above 1500 rpm or 110 psi supply pressure. I will have to put some step up gearing between the engine and the alternator, so it can absorb greater loads. Another problem is the bash valve does not seat consistently, it has a tapered seat and is not guided, either a hemispherical seat or a guide or both should solve this, however preliminary tests do not favour the bash valve, or any of the heads in uniflow exhaust configuration, they are difficult to start, produce barely sufficient power to run themselves let alone any usefull output, whilst still consuming a considerable quantity of air. The head with the inlet valve that is trying to be opened by the supply air has valve float problems at medium rpm, and supply pressure above 120 psi opens the valve, clearly heavier inlet valve springs are required. The two poppet valve heads that have the supply pressure trying to close the valves have performed well. At pressures up to 110 psi and revs up to 1500 the following observations have been made: 1. higher compression ratio gives best economy (8.7% better), lower compression ratio gives best power (2.5%). (obvious really) 2. Best power (1.2% better) and efficiency (2.4%) were using the poppet exhaust valve only followed by poppet and uniflow exhaust combined and worst by far was uniflow exhaust only. 3. Retarded inlet and retarded exhaust valve timing gave the best power (50% improved over advanced inlet and exhaust) (showing no signs of dropping off as the revs increased) And retarded inlet with advanced exhaust timing gave the best economy (16% better than advanced inlet and exhaust). ( effects of recompression?)
High compression head = 13.26 :1 ratio
Low compression head = 6.42 : 1 ratio
Inlet valve timing retarded = 1* atdc open 55* close
Inlet valve timing advanced = 355* open 49* close
Exhaust valve retarded = 173* open 351* close
Exhaust valve advanced = 141* open 319* cose
Uniflow exhaust open = 130* open 230 * close
Will post more data as it comes available. Remember these results are from compressed air not steam and at low pressure and rpm. the engine has run up to 5000 rpm when lightly loaded.
Regards Mike T.
Re: Experimental engine
June 25, 2015 07:41PM
All very interesting, but (and I don't want to start a war here) a steam engine is a heat engine, not a pressure engine, until you start using steam this means nothing, and I mean NOTHING, sorry
Re: Experimental engine
June 25, 2015 09:02PM
Chris is right, unfortunately. Compressed air isn't going to condense in the middle of the stroke and rob you of power like steam can. The advantages of uniflow engines are typically stated in terms of delaying "initial condensation" since the cold exhaust isn't being pushed through the same passages as the hot incoming steam as in a traditional slide valve. Counterflow engines with separate exhaust and admission typically fare better because the passages aren't shared but uniflow tends to separate the two even better. Of course, uniflow has the offsetting disadvantage of compression which can be quite problematic depending on admission pressure ... the reason for aux exhaust valves.

Air testing is a great way to debug the hardware and ensure that it is functioning but the numbers aren't really meaningful until steam is admitted.

Regards,

Ken
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