HOME

TheInfoList



OR:

The Bourke engine was an attempt by Russell Bourke, in the 1920s, to improve the two-stroke internal combustion engine. Despite finishing his design and building several working engines, the onset of World War II, lack of test results, and the poor health of his wife compounded to prevent his engine from ever coming successfully to market. The main claimed virtues of the design are that it has only two moving parts, is lightweight, has two power pulses per revolution, and does not need oil mixed into the fuel. The Bourke engine is basically a two-stroke design, with one horizontally opposed
piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...
assembly using two pistons that move in the same direction at the same time, so that their operations are 180 degrees out of phase. The pistons are connected to a Scotch Yoke mechanism in place of the more usual crankshaft mechanism, thus the piston acceleration is perfectly sinusoidal. This causes the pistons to spend more time at top dead center than conventional engines. The incoming charge is compressed in a chamber under the pistons, as in a conventional crankcase-charged two-stroke engine. The connecting-rod seal prevents the fuel from contaminating the bottom-end lubricating oil.


Operation

The operating cycle is very similar to that of a current production spark ignition
two-stroke A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes (up and down movements) of the piston during one power cycle, this power cycle being completed in one revolution of t ...
with crankcase compression, with two modifications: # The fuel is injected directly into the air as it moves through the transfer port. # The engine is designed to run without using spark ignition once it is warmed up. This is known as auto-ignition or dieseling, and the air/fuel mixture starts to burn due to the high temperature of the compressed gas, and/or the presence of
hot metal ''Hot Metal'' (1986–88) is a British sitcom produced by London Weekend Television about the newspaper industry. Written by David Renwick and Andrew Marshall, it is very much a continuation in style from their previous sitcom '' Whoops Apoc ...
in the combustion chamber.


Design features

The following design features have been identified:


Mechanical features

* Scotch yoke, and linearly sliding connecting rods. * Fewer moving parts (only 2 moving assemblies per opposed cylinder pair) and the opposed cylinders are combinable to make 2, 4, 6, 8, 10, 12 or any even number of cylinders. * The
piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...
is connected to the Scotch yoke through a slipper bearing (a type of hydrodynamic tilting-pad fluid bearing). * Mechanical
fuel injection Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of an injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines. All comp ...
. * Ports rather than
valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...
s. * Easy maintenance ( top overhauling) with simple tools. * The Scotch yoke does not create lateral forces on the piston, reducing friction and piston wear. *
O-ring An O-ring, also known as a packing or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more pa ...
s are used to seal joints rather than
gasket Some seals and gaskets A gasket is a mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression. It is a deformable material that is used to ...
s. * The Scotch yoke makes the pistons dwell very slightly longer at top dead center, so the fuel burns more completely in a smaller volume.


Gas flow and thermodynamic features

* Low exhaust temperature (below that of boiling water) so metal exhaust components are not required; plastic ones can be used if strength is not required from exhaust system. * 15:1 to 24:1
compression ratio The compression ratio is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values. A fundamental specification for such engines, it is measured two ways: the stati ...
for high efficiency and it can be easily changed as required for different fuels and operation requirements. * Fuel is vaporised when it is injected into the transfer ports, and the turbulence in the intake manifolds and the piston shape above the rings stratifies the fuel–air mixture into the combustion chamber. * Lean burn for increased efficiency and reduced emissions.


Lubrication

* This design uses oil seals to prevent the pollution from the combustion chamber (created by piston ring blow-by in four-strokes and just combustion in two-strokes) from polluting the
crankcase In a piston engine, the crankcase is the housing that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, resulting in the fuel/ ...
oil, extending the life of the oil as it is used slowly for keeping the rings full of oil. Oil was shown to be used slowly, but checking the quantity and cleanness of it was still recommended by Russell Bourke, its creator. * The lubricating oil in the base is protected from combustion chamber pollution by an oil seal over the connecting rod. * The piston rings are supplied with oil from a small supply hole in the cylinder wall at bottom dead center.


Claimed and measured performance

*Efficiency - 0.25 (lb/h)/hp is claimed - about the same as the best diesel engine, or roughly twice as efficient as the best two strokes. This is equivalent to a thermodynamic efficiency of 55.4%, which is an exceedingly high figure for a small internal combustion engine. In a test witnessed by a third party, the actual fuel consumption was 1.1 hp/(lb/hr), or 0.9 (lb/hr)/hp, equivalent to a thermodynamic efficiency of about 12.5%, which is typical of a 1920s steam engine. A test of a 30 cubic inch Vaux engine, built by a close associate of Bourke, gave a fuel consumption of 1.48 lb/(bhp hr), or 0.7 (lb/hr)/hp at maximum power. * Power to weight - The Silver Eagle was claimed to produce 25 hp from 45 lb, or a power to weight ratio of 0.55 hp/lb. The larger 140 cubic inch engine was good for 120 hp from 125 lb, or approximately 1 hp/lb. The Model H was claimed to produce 60 hp with a weight of 95 lb, hence giving a power to weight ratio of 0.63 hp/lb. The 30 cu in twin was reported to produce 114 hp at 15000rpm while weighing only 38 lb, an incredible 3 hp/lb However a 30 cu in replica from Vaux Engines produced just 8.8 hp at 4000 rpm, even after substantial reworking. Other sources claim 0.9 to 2.5 hp/lb, although no independently witnessed test to support these high figures has been documented. The upper range of this is roughly twice as good as the best four-stroke production engine shown here, or 0.1 hp/lb better than a Graupner G58 two-stroke. The lower claim is unremarkable, easily exceeded by production four-stroke engines, never mind two strokes. *Emissions - Achieved virtually no hydrocarbons (80 ppm) or
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...
(less than 10 ppm) in published test results, however no power output was given for these results, and NOx was not measured. *Low Emissions - The engine is claimed to be able to operate on hydrogen or any hydro-carbon fuel without any modifications, producing only water vapor and carbon dioxide as emissions.


Engineering critique of the Bourke engine

The Bourke Engine has some interesting features, but the extravagant claims for its performance are unlikely to be borne out by real tests. Many of the claims are contradictory. # Seal friction from the seal between the air compressor chamber and the crankcase, against the
connecting rod A connecting rod, also called a 'con rod', is the part of a piston engine which connects the piston to the crankshaft. Together with the crank, the connecting rod converts the reciprocating motion of the piston into the rotation of the crankshaf ...
, will reduce the efficiency. # Efficiency will be reduced due to pumping losses, as the air charge is compressed and expanded twice but energy is only extracted for power in one of the expansions per piston stroke. # Engine weight is likely to be high because it will have to be very strongly built to cope with the high peak pressures seen as a result of the rapid high temperature combustion. # Each piston pair is highly imbalanced as the two pistons move in the same direction at the same time, unlike in a
boxer engine A flat engine is a piston engine where the cylinders are located on either side of a central crankshaft. Flat engines are also known as horizontally opposed engines, however this is distinct from the less common opposed-piston engine design, wh ...
. This will limit the speed range and hence the power of the engine, and increase its weight due to the strong construction necessary to react the high forces in the components. # High speed two-stroke engines tend to be inefficient compared with four-strokes because some of the intake charge escapes unburnt with the exhaust. # Use of excess air will reduce the torque available for a given engine size. # Forcing the exhaust out rapidly through small ports will incur a further efficiency loss. # Operating an internal combustion engine in detonation reduces efficiency due to heat lost from the combustion gases being scrubbed against the combustion chamber walls by the shock waves. # Emissions - although some tests have shown low emissions in some circumstances, these were not necessarily at full power. As the scavenge ratio (i.e. engine torque) is increased more HC and CO will be emitted. # Increased dwell time at TDC will allow more heat to be transferred to the cylinder walls, reducing the efficiency. # When running in auto-ignition mode the timing of the start of the burn is controlled by the operating state of the engine, rather than directly as in a spark ignition or diesel engine. As such it may be possible to optimize it for one operating condition, but not for the wide range of torques and speeds that an engine typically sees. The result will be reduced efficiency and higher emissions. # If the efficiency is high, then combustion temperatures must be high, as required by the
Carnot cycle A Carnot cycle is an ideal thermodynamic cycle proposed by French physicist Sadi Carnot in 1824 and expanded upon by others in the 1830s and 1840s. By Carnot's theorem, it provides an upper limit on the efficiency of any classical thermodyna ...
, and the air fuel mixture must be lean. High combustion temperatures and lean mixtures cause nitrogen dioxide to be formed.


Patents

Russell Bourke obtained British and Canadian patents for the engine in 1939: GB514842 and CA381959. He also obtained in 1939.


References


External links


Running engine and Cad modeling
{{DEFAULTSORT:Bourke Engine Proposed engines Piston engines Engine technology Two-stroke engine technology