The Bourke Engine 4

[SBBlue]

Okay, kids, here's your assigment: To learn all about the Bourke Engine.

Go visit this website and watch the animation;

http://bourke-engine.com/ani.htm

Supposedly this engine has superior fuel economy and emissions characteristics. As far as I can tell, it is a two stroke engine. Instead of using crankcase scavenging, it uses the lower portion of the cylinder to pump the air necessary for charging the combustion chamber.

It is also claimed that the "Balanced Precision Reverse Cam Effect Roller Crankshaft" did good things too, although from the animation it looks to me that it just results in the piston spending more time at TDC and BDC, and I'm not sure the advantage of that. It apparently is also known as a "Scotch Yoke." The engine is also supposedly "self supercharging."

It is also claimed that the exhaust gas temperature is 190 to 240 deg F, the compression ratio varies from 8:1 to 20:1, and that the air/fuel ratio is 30:1 to 50:1.

I have spent some time looking at the animation, and while I would believe the engine would run, I just don't see how it is "self supercharging", I don't see the advantage of the "Scotch Yoke", and I don't quite understand how it would operate with a 30:1 to 50:1 fuel/air ratio.

If you could get ignition at an air/fuel ratio of 50:1 I could understand why the exhaust gas temperature would be quite low. In addition, the combustion temperature at an A/F ratio of 50:1 would be quite low, which would explain low nitric oxide production, and the PM's might be low by virtue of the excess oxygen present in such a lean condition. But it looks to me that the power density of such an engine would be absymal.

More information on the engine can be found at:

http://www.constant-pressure.com/Home.htm

I must also confess that I don't quite see how this would be a "constant pressure" engine, since it looks to me closer to a "constant volume" engine.

An interesting and somewhat different view of the history of the Bourke Engine can be found at:

http://www.niquette.com/books/sophmag/bourke.htm

Does anybody have any insight about this that I am missing?

 

[GraviMan]

Looks basically like a 2-stroke, but with the fuel injected in the transfer ports. Not sure why this is environmentally friendly, since 2-strokes main problem is allowing uncombusted fuel out the exhaust. Admittedly CFD has improved this in recent years, and if fuel is injected after scavenging situation is better.

Self supercharging is a misnomer - they are really self scavenging engines. Nice bit of design, but I'm not sure why it should have higher sfc than most engines. A 2-stroke diesel, now theres an engine to hanker after - especially if it is matched to a turbo for scavenging.

This unit will still have the old problem of allowing the last bit of exhaust pressure to escape untapped. At first I wondered if the Bourke cycle was a piston brayton cycle. This would be very efficient, since the expansion could be greater than compression. Cool exhaust would also result. I think these units just use the coolant to keep the whole combustion cycle at a controlled temperature.

The scotch yoke may wear prematurely too. I prefer the epicycloidal mechanism (rotary engines are one example), although this would require an X-4 config. There have been some nice demos of this, but I'm not aware of any actual engines.

I'm interested to hear a thermodynamic explanation of why this engine is meant to be so good though!

Mart

 

[GraviMan]

By the way, if the engines main advantage is that it is leanburn, it must be commented that this is the way Rover was heading before BMW blundered in. Nice one, Bernd...

Mart

 

[rmw]

SBBlue, The need for the scotch yoke mechanism is to enable the piston rod to seal the backside of the cylinder for the scavenging cycle. A rotary crankshaft with the rod going through angular motion would not permit this sealing.

Graviman, Detroit Diesel in the USA built 2 cycle diesels for years, and still builds them for non automotive applications.

If you are hankering for one, the junkyards are full of them, and a few of us who have old motorcoach size busses to deal with still have to endure them. And, the latest series, the 92 series (displacement per cylinder, not a year model) was turbo'd and aftercooled, as were some of the older 71's.

Since it still has to have a roots blower to move air to crank, as well as operate when the turbo is not spooled up, the blower can be an impediment to the turbo, unless the "freight truck" option is used, which is basically a by-pass port which diverts turbo air around the blower, which, of course, is volume limited, and straight into the airboxes.

This Bourke engine is interesting. Thanks for the link, SBBlue.

rmw

 

[GraviMan]

"Detroit Diesel in the USA built 2 cycle diesels for years, and still builds them for non automotive applications"

Must admit, I'm very impressed with the engineering in DD engines. Guess they've tried everything...

Mart

 

[rmw]

Are you referring to the current version, which started with the Series 60, and if you are, then we share mutual admiration. I stood at the unveilling at a national truck show some years back, and stated that if I would have been a Cummings or Caterpillar engine salesman, I would be quakeing in my boots, to the hoots and derisive laughter of those around me who heard my remarks.

I only wish I had been as right about everything in life as I was that one. If I were to go back into the trucking industry, (God forbid) I would only go with DDA, (Detroit Diesel Allison.

They knew enough to start over with a clean sheet of paper, and abandon the two cycle concept.

rmw

 

[GraviMan]

"Are you referring to the current version, which started with the Series 60..."

Yup! Waiting to see what Tier4 emissions standard brings...

"If I were to go back into the trucking industry, (God forbid) I would only go with DDA, (Detroit Diesel Allison)."

Both seem to know their stuff very well.

Mart

 

[WGJ]

Just for interest/info, during the late '50's and the '60's in the UK, the 'Commer' truck brand (acquired by Chrysler I believe) marketed small trucks under the name 'Karrier' which were powered by a 3-cylinder, supercharged, 2-stroke diesel which featured 6 horizontally opposed pistons.

Have a look at

http://www.topolino.demon.co.uk/ts3.htm

for a description.

They wee also fitted in some smaller coaches/buses.
The sound these made was something else.

 

[GraviMan]

Me likey! Heavy though with that crank mech. Maybe OPOC deserves another chance...

Mart

 

[dunno]

When I was a teenager, I had a ride in one of those three cylinder Commer TS3 trucks, and although it had a noisy exhaust, it ran extremely smoothly.
Seems that they were very economical engines for their time and many of them found their way into boats.

I believe that this design of this engine was heavily inspired by an earlier German design (Sultzer). - feel free to correct me if I'm wrong.

 

[modesign]

The Commer TS3 was a great engine and a 4 cylinder the TS4 was developed (But not produced). While heavy the crank mechanism gave very low wear rates and I overhauled 2-3 engines with over 100,000 miles on the clock.We just rotated the pins by 180 and put them back in! This gave a low running cost. The weak point was the blower drive which would break if the air cleaner was not fully effective (serviced) and let dirt in. Very smooth power delivery with reasonable economy but always noisy with its Burgess silencer.

 

[Bourke30]

Hello group, Having found this group listed #2 on a Google search for "Bourke engine", I offer my site on the Bourke engine. I have researched and run O.E.M. Bourke 30 C.I.D. engines, as well as my own homebuilt prototype powering a 15 Kw Hobart generator. At <

http://bourke-engine-project.com>

you will find an excellent Solid Works animation and video of my working proto. There is a ton of bogus info about Bourke and I have published this stuff to show how it really works. To my knowledge, none of the other sites has a running engine. I think you will find my site worth your time. Six pre-production prototypes are being built.

 

[SBBlue]

Nice site.

When you talk about "lean combustion" -- just how lean are you talking?

And why should the exhaust gas temperature be any lower than for a normal two-stroke engine?

 

[GregLocock]

Wouldn't you get a lot of NOx from that combustion process?

People are working on NOx traps, but they aren't easy.

Am I right in thinking that the underside of each piston acts as a compressor for the opposing combustion chamber? or does each piston compress its own charge?

Balance wise, as shown, the two cylinder is going to be a bit of a basket case. Increasing the weight of the counterweights will get rid of the first order in the axis of piston movement, at the expense of causing a vertical vibration. A flat 8 would be nicely balanced.

A twin crankshaft version of this would be interesting, as it would eleimnate the balance problem, and the thermal losses through two cylinder heads.

Are you going to measure the fuel consumption soon?

Cheers

Greg Locock

 

[crysta1c1ear]

Greg Locock:
Am I right in thinking that the underside of each piston acts as a compressor for the opposing combustion chamber? or does each piston compress its own charge?

CC:
My interpretation of the pictures was that each piston underside was acting as a compressor for its own charge. That way the pressure is available when it is needed (large cylinder volume).

If a piston underside compressed for the opposing piston, the pressure would be available while the other was firing which is not much use.

I have seen another engine where the backstroke of the piston is used to supercharge the intake. I was going to say 'so its nothing new', but the Bourke engine predates the alternative engine I have seen, and the Bourke is quite old. Maybe I should say 'it might have been new'!

 

[Bourke30]

Obviously lots of questions about the Bourke Cycle.
Oxides of nitrogen are avoided by not being produced in the first place. Combustion chamber temperature is lower than that needed to produce NOx.
F/A ratio as lean as 24/1. Excess air.
Low E.G.T is the result of the expansion of the spent charge for a longer time in the cylinder due to the faster burn rate of the charge. Charges are detonated, producing a flame rate of 5000'/sec., whereas a conventional burn rate is around 150'/sec. Expansion causes cooling. Bourke allows more time for this to happen. Bourkes will not "ping" under detonation, due to zero side load component on the piston skirt. All forces are to center and always compressional.
Each cylinder being tuned carefully, a "null" is achieved where each pulse is cancelled by an equal and opposite pulse. Balance is achieved by an exchange of momentum. Bourke uses the destructive detonations to cancel eachother out. Tuning for this null is where most other Bourke experimenters fail. I developed a simple method to show which cylinder is out of phase. Please view the running video posted on
<

http://bourkeengine.net>

Viewing the running engine should convince the skeptics that Bourke's "100% dynamic balance" is a fact. Previous researchers' failings have muddied the waters for the Bourke design in this area. They simply failed to find the "null".
Fuel consumption is lower than anything currently on the market. They can be set-up to use almost any fuel, as long as it is 63 octane or less. Remember, we are trying to induce a timed detonation. Currently, fuel is "doctored" to suppress detonation and keep the burn rate within limits.
Russ Bourke's work is "old", but was never fully understood. Careful examination of each function will lead ti insight as to why it does combustion to the higher order. Bourke let's us use higher pressures and produces them "earlier" in the cycle.
We all have seen holed pistons. Bourke presents factual answers as to why conventional rods/pistons are "not suited to the task".
I was trained at Embry-Riddle, and hold a commercial pilot ticket.

 

[SBBlue]

With such a slow burn rate, what is the maximum rpm for the engine?

I'm assuming that the maximum cylinder temperature is less than 2500 deg F, since that is roughly the range where you start havin NO2 issues. Is that correct?

And as far as "more time" for expansion; it appears to me that the longer you stretch out the burn rate the less efficient the engine will become. The idea situation, at least as far as efficiency is concerned, would be for all of the fuel to be combusted just a hair short of top dead center.

 

[patprimmer]

SBBlue

I would think that complete combustion, and therefore peak pressure just on TDC would result destructively high pressures, or excessively heavy engine components.

Also, unless the combustion was virtually instantaneous, there would be some efficiency lost to overcome the pressure build up before TDC.

I would think the best efficiency would be obtained if it were possible to ignite the fuel at just before TDC, so there was nil force trying to run backward, then the pressure instantaneously built up to the optimum then the burn rate adjusted proportionally to piston speed so as to maintain that pressure for the longest possible part of the power stroke.

I think optimum pressure might be just below the point where NOx emissions are a problem, or the point where more efficiency is lost to overcome inertia in reciprocating weight than is gained by increasing the maximum cylinder pressure.

Obviously this level of control on burn rate is currently impossible. The only method I envisage to work toward it is by sophisticated control of charge movement in the chamber and or sophisticated control over the phasing of multiple ignition points.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

Sorry, unless there are large lumps of metal involved not present in that video then I am afraid I am unconvinced by your 'momentum transfer' theory.

The two pistons move in the same direction at the same time. Therefore they cannot cancel each others motion. The addition of counterbalance to the crankwebs can be used to cancel out the forces imposed by this, at the expense of introducing out of plane forces equal in magnitude.

Unless I have missed something?

Cheers

Greg Locock

 

[SBBlue]

Pat wrote about ignition combustion timing and efficiency:

"Also, unless the combustion was virtually instantaneous, there would be some efficiency lost to overcome the pressure build up before TDC."

I guess I'm missing something here. What are you talking about when you mention overcoming the pressure built up before TDC?

"I would think the best efficiency would be obtained if it were possible to ignite the fuel at just before TDC, so there was nil force trying to run backward, then the pressure instantaneously built up to the optimum then the burn rate adjusted proportionally to piston speed so as to maintain that pressure for the longest possible part of the power stroke."

Any heat added to the cylinder past top dead center will be converted into mechanical energy less efficiently than heat introduced right at top dead center. I can run some numbers on this for you, but right now I'm tired.

"I think optimum pressure might be just below the point where NOx emissions are a problem, or the point where more efficiency is lost to overcome inertia in reciprocating weight than is gained by increasing the maximum cylinder pressure."

NOx emissions are much more a function of temperature than pressure. And for engines that have stoichometric combustion (both spark ignition and compression ignition), the peak temperature is fairly well set. This isn't true for HCCI engines, of course.

"Obviously this level of control on burn rate is currently impossible."

Boy, that would be a real good trick!!