All About the Bourke Engine and How it Works - Part I
"If my engine were in general use
we would never hear of monoxide deaths or smog caused by these
Excerpt from All About the Bourke Engine and How it Works
By Russell Bourke as told to Bob Whittier, July 1968
A FEW YEARS ago Atlantic Monthly magazine published an article by automotive writer Ken W. Purdy.
Many of you probably read a condensation of it in the September, 1960 issue of
'Readers Digest'. It told about
the new Wankel engine, and in the comparing that power-plant with the conventional automobile engine, Purdy
said: "The standard internal combustion reciprocating engine is basically so unsuited to its task that its universal
acceptance and success are a source of wonderment....the true nature of the animal reveals itself when it is
operating at optimum design efficiency, as in a racing automobile, in the howling of gears, roar of exhaust, wild
clattering and bone jarring vibrations. A reciprocating engine seems always to be trying to destroy itself. And so it
The word 'reciprocating' is the key. A reciprocating engine is. In effect, a multi-barreled cannon, with the fuel
charge the gunpowder, the piston the projectile and the spark plug the primer or trigger. The charge explodes; the piston,
driving its connecting rod, starts to fly out the barrel; but after only two or three inches of flight it must stop, reverse
itself, and come flying back toward the breech. It is this repeated reversal of movement, taking place thousands of times
a minute, that is at the root of the savagery.
How true! But this was not news to me. I became fully aware of these facts some 40 years previously and
my whole life has revolved around them and their implications.
In 1918 I was an instructor of the internal combustion engine theory and maintenance at the Air Service
Mechanics School, Kelly Field, Tex. From daily discussions with students and fellow instructors I came to the
realization that four-stroke engines were basically inefficient with three dead strokes and too many moving parts.
And the fact that many of my flying friends were lost when their planes crashed, and spilled gasoline caught fire,
made a deep impression on me. I was determined to find a way to make internal combustion engines simpler,
more efficient and safer.
At that time our engines were really only a few years out of the
inventors laboratories and we were closer to the
ideas and writings of men who had conceived the internal combustion engine. Today, the textbooks young designers
study are much more sophisticated - and also farther removed from fundamentals. My reading soon took me deep
into the works of the 19th century pioneers and please
do not sneer at that old hat stuff. Remember, gravity had
been operating for eons and nobody noticed it. Today, the law of gravity seems so obvious, but Sir Isaac Newton won
eternal fame for merely noticing the obvious and describing it concisely. Once he had done that, the laws of gravity
and other physical forces, as expounded by Newton, became basic tools for science and technology.
I read Sir Humphrey Davy, Sir Dugald Clark, Sir Frederic Abel, R. W. Bunsen, and other greats who had laid
down the principles which sparked the 20th century scientific advances. I also studied the works of lesser known
but equally capable and original investigators into hydrocarbon chemistry such as Mallard & Le Chatelier, Berthelot &
Vielle, Andrews, Favre & Silberman, Beau de Rochas and Dr. Otto. To my mind they are without peer; I wish young
technicians would build better foundations for their careers by becoming familiar with them. It is not enough to read
of them, however, one must read them!
Here I must comment on theory. Modern engineering courses concentrate on giving students a firm grounding
in theory, knowing that they will obtain the practical experience when they graduate into some profitable specialty.
But Webster defines theory as a more or less plausible or scientifically acceptable general principle offered to
explain a phenomenon . . . which sounds alarmingly like
speculation to me! Funk and Wagnall says the word
means a proposed explanation designed to account for any phenomenon.
I, however, call it a
crutch to support a lame idea. I do not mean to sound hypercritical, but wish only to stress that since the
engines have been designed by blindly following the wording of
somebody's theory rather than by considering
the nuances of the principle it attempts to state. This path has led designers to the point where they feel they can
go no farther with piston engines and have become involved with the awful noises, smells, temperatures, fuel
appetites and rotational speeds of turbine engines. I tried to show the world another path 10 long years ago
but fate decreed that engineers should refuse to listen to my logic. They knew their theory, and upon that pillar they
were determined to stand firm! Pistons, cylinders and rods are not at fault, just the arrangement and cycle.
One hundred years ago, in 1862, a Frenchman named
Alphonse Beau de Rochas, considered the possibility of
constructing internal combustion engines to extract energy from burning fuel. He stated that to develop power in
that manner it would be necessary to build four functions into an apparatus
- intake, compression, power and
exhaust. It is worth noting that he also said that a good internal combustion engine should have these attributes:
- The greatest possible cylinder volume with the least possible cooling surface. (i.e. Large bore, short stroke).
- The greatest possible rapidity of expansion of the fuel. (i.e. High compression and lean mixture).
- The greatest possible amount of expansion of the fuel. (i.e. Low temperature of exhaust).
- The greatest possible pressure at the commencement of expansion. (i.e. total extraction of energy, complete
combustion at T.D.C).
- Minimum of moving parts.
And in 1872 Germany's Dr. Otto based his Otto four-stroke cycle engine on de
Rochas' theory. He interpreted
de Rochas' list of four functions to mean that the piston must make four strokes to complete one cycle. His engine
was a success not because it was theoretically brilliant but because it was tractable, versatile and readily
constructed of available materials. Its compactness enabled it to compete with steam and suited it to vehicular use.
Otto knew it had shortcomings when evaluated against de
Rochas' list of five desirable attributes, but it did a job.
Others seized upon it eagerly, and it got completely away from him. Entire industries have since been built up
around four-stroke cycle engines.
The first Otto engine had a three to one compression ratio, to suit the available fuel. The intake compression
power exhaust cycle resulted in three wasted (intake -
compression - exhaust) strokes for each productive (power)
stroke. Valve mechanisms added cost and complications. Much
fuel and heat went out the exhaust ports, and more went to waste in the cooling system via the
flame-bathed cylinder walls. There was a bad noise and vibration. Since that time vast effort has gone into developing
fuels that won't knock by deliberately doping it against hydrogen-oxygen reaction,
increasing valve and bearing
durability, more elaborate vibration control, better output through higher revolutions and shorter strokes, better
lubrication and ignition to stand higher speeds and so on.
What would you say if I stated that engineers are wrong in trying to stop detonation, and that the path for progress
should be along the line of using it as a means of extracting more energy from each pound of fuel?
Long ago I freed my mind of the shackle of thinking of gasoline as the right fuel. I wanted to get away from it for
aviation safety's sake; it has no place in aircraft! It is, after all, but one of many derivatives of crude oil. I thought of
fuel as being a hydro-carbon found in fluid form deep in the earth, and delved deeply into the subject of
hydrocarbons. How best to squeeze maximum power from each pound of hydrocarbon fuel?
The burning of fuel is a chemical process, for which precise chemical equations can be written. Given a
hydrocarbon fuel and the air which surrounds us, one has only hydrogen, carbon and oxygen to work with in
devising combustion equations. Books of early basic researchers state clearly that one pound of carbon burned
with oxygen will heat 8,000 pounds of water one degree Centigrade, but one pound of hydrogen similarly burned will
heat 34,170 pounds of water a like amount. Also, the rate of expansion of burning hydrogen-oxygen is far greater
than that of carbon-oxygen. One authority wrote, "Hydrogen expands at a rate of 5,000 feet per
second", but this is of no
interest to a design engineer for no known engine is capable of utilizing such a violent force.
See how our teachers sometimes unwittingly erect barricades to imaginative thought!
In conventional internal combustion engines fuel does not really explode, it burns progressively. Touch a
match to some guncotton standing in open air and it will burn harmlessly in a progressive manner. But ignite it with
a percussive primer, as in a rifle cartridge, and a violent explosion results. Far more energy is released. A shock
wave passing through a fuel makes it burn differently, more powerfully. Ask any atomic bomb scientist! But no, for
generations now power plant engineers have been schooled to regard detonation as bad, and their work revolves
around avoiding it.
Furthermore, designers have been following a line of false reasoning while trying to make conventional engines
more suitable for aviation use. All the effort has gone into reducing engine weight. Listen to the boasting about the
low weight per horsepower of a particular engine! The magic figure of one pound per horsepower is worshipped,
which may be all right for some applications and would be commendable for aviation if the fuel consumption curve
fell off instead of soaring out the top of the graph.
Take an airplane engine weighing one pound per horsepower. If 200 hp output is wanted, the engine will weigh
200 lbs. Standard figuring calls for fuel consumption of half a pound of fuel per horsepower hour, or 100 pounds of
fuel per hour. In 10 hours such an engine will burn 1,000 pounds of fuel. Take-off weight for the power producing
system is thus 1,200 pounds. If fuel consumption were halved, though, weight reduction could be spectacular. If
engineers had neglected the engine's weight in favor of better fuel utilization and had been able only to produce an
engine weighing two pounds per horsepower, this 200 hp power-plant would weigh 400 pounds. But if it burned its fuel
more effectively and consumed only one-quarter pound of fuel per horsepower hour, it would burn 50 pounds per hour,
or 500 pounds in 10 hours of flight. Take-off weight of the power producing system would then be 900 pounds, or a
saving of 300 pounds! Translate that into carrying capacity, or into a lighter airframe, or any combination of the two, and
the savings are obvious!
Once any engine has been selected to power an airplane, it represents a fixed weight. Surely airplane
designers ought to give priority, therefore, to means of substantially reducing fuel consumption! The most obvious
way I can think of is through use of leaner fuel-to-air mixtures.
Today's gasoline engines run on a mixture of
about 15 parts air to one part fuel. The common diesel engine shows us clearly that increasing the compression
ratio allows the use of leaner mixtures. All diesels run leaner than gasoline engines, and when idling the mixture in
some may be as lean as 1,000 parts of air to one of fuel. In the past, diesel engines have blown up from the explosive
power that resulted from momentarily leaning out the mixture when tapering off the fuel to stop. For that reason some
of them are today fitted with kill devices that eliminate that brief period of danger.
Lean mixtures can develop vastly more power for a simple reason. The leaner the mixture, the more oxygen there
is in the combustion chamber in relation to the amount of carbon and hydrogen. The richness of the conventional
gasoline engine's mixture automatically limits the combustion process to a carbon-oxygen reaction. There is not
enough oxygen for a hydrogen-oxygen reaction. Doping of fuel with tetraethyl lead plus careful tailoring of temperature
and pressure prevents unwanted detonation that takes place in gasoline engines when limits are exceeded. In
diesels, fuel is injected and burns as the piston moves away from top dead center, increasing cylinder volume and
keeping heat and pressure within limits.
A gas has two specific heats, depending on whether it is kept at a constant volume or constant pressure. During
a power stroke in any conventional engine, combustion space volume steadily increases and the burning of fuel does
not build up the pressure required to burn a very lean mixture. If combustion took place in a closed vessel so that
volume did not increase, only pressure can increase and that can raise temperature high enough to cause a
hydrogen-oxygen reaction in a lean mixture.
The Bourke Cycle is based on all of these scientific facts. It is nothing more than an apparatus to obtain a
hydrogen-oxygen reaction. It releases far more energy from each pound of hydrocarbon fuel. It is simple, light, durable
Otto, as has been noted, developed his four-stoke cycle from de
Rochas' theory. Apparently his mechanical
thinking was influenced by steam engines of his day and caused him to adopt the connecting rod and crankshaft
method of converting reciprocating into rotary motion. So, unwittingly, he started the internal-combustion engine out
onto a dead-end road. Today designers realize they have reached its end. Mentally
straitlaced by the fixed ideas and
statements of their teachers, they can think only of the wasteful turbine as a means of escaping the limitation of the
uncontrolled reciprocating motion. I saw the blank wall long ago.
It took 14 years of study, 1918 to 1932 for me to develop the mechanism of my engine. Realizing that the
connecting rod and crankshaft arrangement as used is stupid, I looked through volumes of mechanical movements
and eventually devised a refined version of the common scotch yoke
which in its original form would have been
useless for high speed engines.
Everything seems against the connecting rod and crankshaft. At the end of every stroke piston movement is
reversed by the rod. Tension and compression forces in the rod are transmitted through the crankshaft support
bearings to the engine as a whole, to strain the
vehicle's structure and bother occupants. Piston reciprocating
vibration can't be counterbalanced out 100 percent because if crankshaft counterweights were heavy enough to
neutralize the force of piston reversal, they would shake the crankcase when the piston was
mid-stroke and the
counterweight force at right angles to the cylinder centerline.
The best that can be done is to settle for some
suitable percentage of counterbalancing and then go into multiple cylinders which blur out the remaining
reciprocating vibration. The angularity between connecting rod and cylinder bore puts a heavy side load on the
piston during the power stroke and from the beginning conventional engines have progressed only as oils were
developed to stand higher pressures. The ping heard when a gasoline engine knocks is caused by metal-to-metal
contact when excessive pressure crushes the oil film between piston and cylinder.
Rate of piston travel, hence the
period spent at T.D.C., is a direct and unalterable function of crank-pin rotation and the designer must program his
combustion process to suit. As for the gas turbine, I think it is all right for very fast airplanes where propeller blade
tip velocity is a barrier to higher air speed, but quite nonsensical for any subsonic vehicle. It is in the same class as
burning guncotton in open air to achieve fractional energy release.
The refined scotch yoke solved everything for me. Its geometry is such that the twin pistons remain at T.D.C. longer,
long enough for the extremely rapid hydrogen-oxygen combustion process to burn all of the fuel before the down
stroke really begins. I use compression ratios up to 24-1, which gives the high pressure and temperature needed
to trigger the explosive combustion. When a cylinder fires, its piston acts as a projectile and the entire piston and
rod assembly moves. As it moves, kinetic energy is transmitted to the crankshaft.
Initial combustion temperature is
higher than poppet valves could stand, but as the piston moves on its down stroke, cylinder volume increases. All
the fuel has burned, however, and cylinder walls are not seared with flame. Instead, the expanding gases act just as
scientific laws say they should - as a refrigerant. The pressure of still-burning fuel is not suddenly valved out to the
atmosphere to make a loud noise. There is no exhaust flame throwing heat energy to waste.
My engines exhaust
is so cool that a man can hold his hand close to the ports without harm.
The straight-line motion of the pistons eliminates piston slap, there is no valve clatter or gear whine, the exhaust
is muted. The hydrogen-oxygen combustion does not produce carbon monoxide.
If my engine were in general use
we would never hear of monoxide deaths or smog caused by these engines. As the pistons are interconnected the
crankshaft never feels their reciprocating forces and counterbalancing is not needed. The action of the yoke is such
that 100 percent balance is possible for the crankshaft; it spins as smoothly as a flywheel. You might guess that the
engine would shake from piston action but it does not, because the twin piston assembly is
free as it can't transmit its
reciprocating forces to the body of the engine, and also absorbs those forces within itself. It is simply thrown back
and forth, explosion forces reacting against momentum forces so that things are cancelled out, as in a free piston
engine, which it is.
The engine burns straight fuel like any four-stroke cycle machine. As can be seen in the drawing, the crankcase is
separated from the cylinders. Piston blow-by does not go into the crankcase but is re-circulated via incoming charges.
Oil in the crankcase is not contaminated and lasts indefinitely. The cylinders and pistons are lubricated by small oil
holes which leave a metered amount of oil between the piston and walls. There is no poor idling or spark plug fouling
such as is experienced when oil is mixed with two-cycle fuel. Each piston produces a power stroke on every revolution
and as twin pistons are the foundation of the idea, there are two power impulses for every revolution. Any number
of twin-piston power units can be bolted to a variety of bases to give power clusters of any desired output.
There is a reason for each and every detail. The engine can stand detonation pressures because there is no
connecting rod angularity or crankpin bearings to suffer intolerable shock loads. Pistons have turbulating fins on
them to impart tornado action to the incoming charges.
This makes unburned charges rush past open exhaust
ports without going out through them. Piston skirts are split and preloaded against the cylinder walls so there is
heat transfer when the engine first starts. If pistons were a loose fit their heads would overheat from detonation
before the rest of the metal expanded enough to dissipate
heat into the cylinder walls. Connecting rods are
bored out to help dissipate any heat into the crankcase oil, this, along with the coolness of incoming charges under
the pistons, keeps the national leather seals from scorching. Slipper-type bearings in the yoke have large area and
are made of shock resistant alloy, so they withstand detonation easily.
I have run my engines up to 2,000 hours without noticeable wear. They respond to the throttle without
faltering. I have had them reach speeds of over 20,000 rpm without harm and the only apparent speed limitation is in
the ability of an ignition system to produce sparks that fast. They run well on cheap fuels such as brown distillate,
and as for economy, my little 38 pound 30 cubic inch job gave 76 hp at 10,000 rpm and at an easy 6500 rpm burned
only one gallon per hour. The Bourke Cycle engine comes closer than anything else that I am aware of to completely
fulfilling the five desirable attributes for an efficient internal combustion engine laid down by the unfettered mind of
de Rochas a century ago.
Part II of All About the Bourke Engine and
How it Works may be purchased.
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