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]

I'm puzzled about the Beare head. Basically it is a 4-stroke, but with a different valve mechanism. I presume the main advantage is that using the reed valve, and piston head, you get very high volumetric efficiency with very low pumping losses. How do these compare with a poppet valve design? Does the Beare head offer better working fluid replacement across rpm range, without the complexity of VVT?

Mart

 

[malbeare]

GraviMan (Automotive)
you are right in that you get very high volumetric efficiency with very low pumping losses especially at low rpm low throttle settings. we setup a good stratification with the ignitable mixture swirling towards the outside close to the spark plugs in the combustion chamber side wall.
The head actually produces power this is fundimental to a gain in mechanical efficiency aprox 8 to 10%.
The rate of change in combustion chamber volume is less than a fourstroke during combustion so that it is closer to the ideal of constant volume during combustion. but the rate of change in volume during the rest of the expansion stroke is faster and larger than a fourstroke. so there is a gain similar to the atkins or miller cycle.
Coupled with our air assisted fuel injector that produces dropplet sizes of 5 micron and the ability to induce a premix of 20% intake volume thruogh the injector. we efectivly have all the advantages of direct injection without the nozzle being in the combustion chamber and subject to cylinder temps and pressure.
It is still very much work in progress so I cannot diclose all . But I hope this gives you an overview of the advantages

http://www.jack-brabham-engines.com/

A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare

 

[GraviMan]

"...good stratification with the ignitable mixture swirling towards the outside close to the spark plugs in the combustion chamber side wall."

OK, so the flame starts from outside in? Does this produce any flame quenching?

"The rate of change in combustion chamber volume is less than a fourstroke during combustion so that it is closer to the ideal of constant volume during combustion."

And you avoid cams and valves...

"Coupled with our air assisted fuel injector that produces dropplet sizes of 5 micron and the ability to induce a premix of 20% intake volume thruogh the injector."

This alone is a nice line of endeavor. Can this be fitted to other engines, or is it part of the Beare package?

Mart

 

[btrueblood]

Ok, I've resisted this post twice now, but once again we have a claim of "a gain in mechanical efficiency aprox 8 to 10%." We've seen similar statements that the Bourke engine and others have very high efficiency/low BSFC. So far, I've not seen anything that substantiates these claims.

Can anybody measure the fuel consumption of their engine, under a load (say, a generator operating a bank of light bulbs) and report it?

If there is some confusion about how to rig such a test, post your query here and we can all kick some ideas around.

 

[NickE]

btrueblood- read SBBlue's first post, click on his last link, that gives a good method for measuring torque. (Of course you have to remember your engineering mechanics)

nick

 

[btrueblood]

NickE - that's exactly what I'm talking about. There are claims made on various websites and various postings; none of these are substantiated with test data (including descriptions of the test rig). I could care less HOW the output power is measured (tie a rope to a weight and measure velocity, pump liquid, generate electricity, do whatever, but just MEASURE IT!). And then report it. If your claims match test data, then we can talk. Until then, this whole thread is just so much exhaust.

 

[malbeare]

ROAD SPEED MPH 4STROKE RUN TIME SECONDS 100cc FUEL 6STROKE RUN TIME SECONDS100cc FUEL LOADED RPMIn 5th GEAR % LONGER RUN TIME
30 159 216 2000 35.8%
35 138 184 2500 33%
40 107 134 3000 25.2%
45 89 101 3500 13%
YAMAHA TT 500cc
Test by Malcolm Beare, Elliot Munro, Grant Guy, July 1995
The dyno used was an old motorbike dyno with the rear wheel driving a large fan with a speed readout dial. The throttle was opend enough to maintain the designated speed.
The sixstroke head was designed to as closely match the fourstroke as possible compression ratio , valve timing , port sizes.
The sixstroke would run happily at lower revs(1000) than the fourstroke in 5th gear. The fourstroke would pull 4000 RPM at full throttle the sixstroke 3500.I think that the maximum horsepower is in the region of 18 HP for the sixstroke and 22HP for the fourstroke
Same gearing same carburetor.
Fuel was gravity fed to the carb from a long clear tube with two level marks to indicate 100cc


A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare

 

[btrueblood]

Malbeare,

THANK YOU! That's a nice, brief, concise test report. It's nice to see somebody making the effort, taking the time, measuring some data, and having the guts to report it.

Now - I'm impressed by the numbers, but I'm not sure if we aren't looking at two different engine "sizes"... i.e. I wonder what happens when each engine is run at near-stall conditions. I'd expect the 4-banger is actually giving more peak h.p. and probably has a higher top end. Having a way to modulate and measure the output power, to run the motor up against its stall limit, would allow a better comparison than just the run time at a fixed power setting. What I'm saying is that the BSFC of the 6-stroke motor may or may not be better than the 4-banger at reduced throttle settings, without measuring power we just don't know (but your numbers certainly look good, and make me curious to find out!) Could you not couple the motor's output shaft to a generator, or a brake, and vary the load to map the power-specific fuel consumption?

 

[patprimmer]

Malbeare

Would you like to start a new thread on this as it is technically off subject, not being a Bourke engine, but more to the point, this thread has become VERY long and it takes quite a time for the page to load and allow me to scroll to the end.

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.

 

[malbeare]

btrueblood (Mechanical)
The laod or power output is the same for each engine at the designated speed because the fan is absorbing the same X horspower or requires the same torque to turn it at the same speed . only the throttle settings must have been different.
It would be a good debating point whether the reed valves alone accounted for the superior performance by not allowing any spittback and therefore making carburation cleaner and more precise. Or how much the mechanical construction added to the gain in fuel efficiency. I suspect a little of both.
I have come to the conclusion that to obtain good gas flow at higher RPM the a combination of reed and rotary disk is needed on the intake. Reeds tend to fall over above 6000 and flutter.
If you look at the change in volumes for each engine then the 4 stroke is 500cc for each stroke , but the sixstroke is smaller on the intake and larger on the compression and expansion but smaller again on the exhaust. This varies depending on the phasing relationship between the upper and lower main crankshaft.
At 2000 rpm the 4 banger is at its stall limit in 5 gear
The practical result is that on the road the sixstroke would save fuel.

http://www.jack-brabham-engines.com/

A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare