The Lyons-Knight was an American automobile manufactured from 1913 until 1915 in Indianapolis, Indiana .
76-627: Three brothers, James W., William P. and George W. Lyons purchased the Atlas Engine Works and reorganized as the Lyons-Atlas Company. The previous Atlas Company manufactured two-stroke gasoline and diesel engines, and had developed a line of gasoline engines using the Knight sleeve-valve design. The Lyons-Knight featured Knight sleeve-valve engines and worm-drive rear axles , that were designed by Harry A. Knox who had previously worked at
152-598: A Model K-6, six-cylinder engine was offered with the same wheelbase in either a five or seven passenger touring sedan for $ 3,200 (equivalent to $ 97,340 in 2023). In 1915 only the K-4 model was offered but with the addition of limousine and roadster bodies. Automobile manufacturing ended in 1915 soon after Harry Knox resigned from the company. Lyons-Atlas Company continued building engines and manufactured Standard marine engines for Britain during World War I . Two-stroke A two-stroke (or two-stroke cycle ) engine
228-408: A combined cycle plant, thermal efficiencies approach 60%. Such a real-world value may be used as a figure of merit for the device. For engines where a fuel is burned, there are two types of thermal efficiency: indicated thermal efficiency and brake thermal efficiency. This form of efficiency is only appropriate when comparing similar types or similar devices. For other systems, the specifics of
304-406: A heat engine is the percentage of heat energy that is transformed into work . Thermal efficiency is defined as The efficiency of even the best heat engines is low; usually below 50% and often far below. So the energy lost to the environment by heat engines is a major waste of energy resources. Since a large fraction of the fuels produced worldwide go to powering heat engines, perhaps up to half of
380-410: A heat engine , thermal efficiency is the ratio of the net work output to the heat input; in the case of a heat pump , thermal efficiency (known as the coefficient of performance or COP) is the ratio of net heat output (for heating), or the net heat removed (for cooling) to the energy input (external work). The efficiency of a heat engine is fractional as the output is always less than the input while
456-415: A power-valve system . The valves are normally in or around the exhaust ports. They work in one of two ways; either they alter the exhaust port by closing off the top part of the port, which alters port timing, such as Rotax R.A.V.E, Yamaha YPVS, Honda RC-Valve, Kawasaki K.I.P.S., Cagiva C.T.S., or Suzuki AETC systems, or by altering the volume of the exhaust, which changes the resonant frequency of
532-421: A rotary valve is that it enables the two-stroke engine's intake timing to be asymmetrical, which is not possible with piston-port type engines. The piston-port type engine's intake timing opens and closes before and after top dead center at the same crank angle, making it symmetrical, whereas the rotary valve allows the opening to begin and close earlier. Rotary valve engines can be tailored to deliver power over
608-635: A steam power plant , or the temperature at which the fuel burns in an internal combustion engine . T C {\displaystyle T_{\rm {C}}} is usually the ambient temperature where the engine is located, or the temperature of a lake or river into which the waste heat is discharged. For example, if an automobile engine burns gasoline at a temperature of T H = 816 ∘ C = 1500 ∘ F = 1089 K {\displaystyle T_{\rm {H}}=816^{\circ }{\text{C}}=1500^{\circ }{\text{F}}=1089{\text{K}}} and
684-421: A DKW design that proved reasonably successful employing loop charging. The original SAAB 92 had a two-cylinder engine of comparatively low efficiency. At cruising speed, reflected-wave, exhaust-port blocking occurred at too low a frequency. Using the asymmetrical three-port exhaust manifold employed in the identical DKW engine improved fuel economy. The 750-cc standard engine produced 36 to 42 hp, depending on
760-450: A colder to a warmer place, so their function is the opposite of a heat engine. The work energy ( W in ) that is applied to them is converted into heat, and the sum of this energy and the heat energy that is taken up from the cold reservoir ( Q C ) is equal to the magnitude of the total heat energy given off to the hot reservoir (| Q H |) Their efficiency is measured by a coefficient of performance (COP). Heat pumps are measured by
836-448: A crossflow engine) is always best and support is good. In some engines, the small end is offset to reduce thrust in the intended rotational direction and the forward face of the piston has been made thinner and lighter to compensate, but when running backward, this weaker forward face suffers increased mechanical stress it was not designed to resist. This can be avoided by the use of crossheads and also using thrust bearings to isolate
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#1732858622837912-465: A patent in 1880 in Germany. The first truly practical two-stroke engine is attributed to Yorkshireman Alfred Angas Scott , who started producing twin-cylinder water-cooled motorcycles in 1908. Two-stroke gasoline engines with electrical spark ignition are particularly useful in lightweight or portable applications such as chainsaws and motorcycles. However, when weight and size are not an issue,
988-449: A scavenging function. The units run in pairs, with the lower half of one piston charging an adjacent combustion chamber. The upper section of the piston still relies on total-loss lubrication, but the other engine parts are sump lubricated with cleanliness and reliability benefits. The mass of the piston is only about 20% more than a loop-scavenged engine's piston because skirt thicknesses can be less. Many modern two-stroke engines employ
1064-658: A similar system. Traditional flywheel magnetos (using contact-breaker points, but no external coil) worked equally well in reverse because the cam controlling the points is symmetrical, breaking contact before top dead center equally well whether running forward or backward. Reed-valve engines run backward just as well as piston-controlled porting, though rotary valve engines have asymmetrical inlet timing and do not run very well. Serious disadvantages exist for running many engines backward under load for any length of time, and some of these reasons are general, applying equally to both two-stroke and four-stroke engines. This disadvantage
1140-413: A thermal efficiency close to 100%. When comparing heating units, such as a highly efficient electric resistance heater to an 80% efficient natural gas-fuelled furnace, an economic analysis is needed to determine the most cost-effective choice. The heating value of a fuel is the amount of heat released during an exothermic reaction (e.g., combustion ) and is a characteristic of each substance. It
1216-518: A turbocharger. Crankcase-compression two-stroke engines, such as common small gasoline-powered engines, are lubricated by a petroil mixture in a total-loss system . Oil is mixed in with their petrol fuel beforehand, in a fuel-to-oil ratio of around 32:1. This oil then forms emissions, either by being burned in the engine or as droplets in the exhaust, historically resulting in more exhaust emissions, particularly hydrocarbons, than four-stroke engines of comparable power output. The combined opening time of
1292-400: A wider speed range or higher power over a narrower speed range than either a piston-port or reed-valve engine. Where a portion of the rotary valve is a portion of the crankcase itself, of particular importance, no wear should be allowed to take place. In a cross-flow engine, the transfer and exhaust ports are on opposite sides of the cylinder, and a deflector on the top of the piston directs
1368-413: Is 90% efficient', but a more detailed measure of seasonal energy effectiveness is the annual fuel use efficiency (AFUE). The role of a heat exchanger is to transfer heat between two mediums, so the performance of the heat exchanger is closely related to energy or thermal efficiency. A counter flow heat exchanger is the most efficient type of heat exchanger in transferring heat energy from one circuit to
1444-421: Is a type of internal combustion engine that completes a power cycle with two strokes of the piston (one up and one down movement) in one revolution of the crankshaft. (A four-stroke engine requires four strokes of the piston to complete a power cycle, in two crankshaft revolutions.) In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with
1520-413: Is accepted in most cases where cost, weight, and size are major considerations. The problem comes about because in "forward" running, the major thrust face of the piston is on the back face of the cylinder, which in a two-stroke particularly, is the coolest and best-lubricated part. The forward face of the piston in a trunk engine is less well-suited to be the major thrust face, since it covers and uncovers
1596-472: Is an active area of research. Due to the other causes detailed below, practical engines have efficiencies far below the Carnot limit. For example, the average automobile engine is less than 35% efficient. Carnot's theorem applies to thermodynamic cycles, where thermal energy is converted to mechanical work. Devices that convert a fuel's chemical energy directly into electrical work, such as fuel cells , can exceed
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#17328586228371672-422: Is attributed to Scottish engineer Dugald Clerk , who patented his design in 1881. However, unlike most later two-stroke engines, his had a separate charging cylinder. The crankcase -scavenged engine, employing the area below the piston as a charging pump, is generally credited to Englishman Joseph Day . On 31 December 1879, German inventor Karl Benz produced a two-stroke gas engine, for which he received
1748-590: Is being phased out. Honda , for instance, ceased selling two-stroke off-road motorcycles in the United States in 2007, after abandoning road-going models considerably earlier. Due to their high power-to-weight ratio and ability to be used in any orientation, two-stroke engines are common in handheld outdoor power tools including leaf blowers , chainsaws , and string trimmers . Two-stroke diesel engines are found mostly in large industrial and marine applications, as well as some trucks and heavy machinery. Although
1824-454: Is called the Carnot cycle efficiency because it is the efficiency of an unattainable, ideal, reversible engine cycle called the Carnot cycle . No device converting heat into mechanical energy, regardless of its construction, can exceed this efficiency. Examples of T H {\displaystyle T_{\rm {H}}\,} are the temperature of hot steam entering the turbine of
1900-565: Is common in on-road, off-road, and stationary two-stroke engines ( Detroit Diesel ), certain small marine two-stroke engines ( Gray Marine Motor Company , which adapted the Detroit Diesel Series 71 for marine use ), certain railroad two-stroke diesel locomotives ( Electro-Motive Diesel ) and large marine two-stroke main propulsion engines ( Wärtsilä ). Ported types are represented by the opposed piston design in which two pistons are in each cylinder, working in opposite directions such as
1976-559: Is consumed. The desired output is mechanical work , W o u t {\displaystyle W_{\rm {out}}} , or heat, Q o u t {\displaystyle Q_{\rm {out}}} , or possibly both. Because the input heat normally has a real financial cost, a memorable, generic definition of thermal efficiency is η t h ≡ benefit cost . {\displaystyle \eta _{\rm {th}}\equiv {\frac {\text{benefit}}{\text{cost}}}.} From
2052-432: Is fixed by the environment, the only way for a designer to increase the Carnot efficiency of an engine is to increase T H {\displaystyle T_{\rm {H}}} , the temperature at which the heat is added to the engine. The efficiency of ordinary heat engines also generally increases with operating temperature , and advanced structural materials that allow engines to operate at higher temperatures
2128-535: Is measured in units of energy per unit of the substance, usually mass , such as: kJ/kg, J / mol . The heating value for fuels is expressed as the HHV, LHV, or GHV to distinguish treatment of the heat of phase changes: Which definition of heating value is being used significantly affects any quoted efficiency. Not stating whether an efficiency is HHV or LHV renders such numbers very misleading. Heat pumps , refrigerators and air conditioners use work to move heat from
2204-432: Is that the two-stroke's crankcase is sealed and forms part of the induction process in gasoline and hot-bulb engines . Diesel two-strokes often add a Roots blower or piston pump for scavenging . The reed valve is a simple but highly effective form of check valve commonly fitted in the intake tract of the piston-controlled port. It allows asymmetric intake of the fuel charge, improving power and economy, while widening
2280-409: Is under every circumstance more efficient than cross-flow scavenging. In a uniflow engine, the mixture, or "charge air" in the case of a diesel, enters at one end of the cylinder controlled by the piston and the exhaust exits at the other end controlled by an exhaust valve or piston. The scavenging gas-flow is, therefore, in one direction only, hence the name uniflow. The design using exhaust valve(s)
2356-607: The Atlas-Knight Automobile Company in Springfield, Massachusetts . Beginning in 1913, the Lyons-Knight Model K-4 offered a four-cylinder engine that produced 50- hp and was installed in a choice of five or seven passenger touring car , sedan , or berline bodies, using a 130-inch wheelbase . Prices started at $ 2,900 for the five passenger touring sedan while the berline sedan was $ 4,300. For 1914
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2432-458: The Junkers Jumo 205 and Napier Deltic . The once-popular split-single design falls into this class, being effectively a folded uniflow. With advanced-angle exhaust timing, uniflow engines can be supercharged with a crankshaft-driven blower, either piston or Roots-type. The piston of this engine is "top-hat"-shaped; the upper section forms the regular cylinder, and the lower section performs
2508-506: The expansion chamber , such as the Suzuki SAEC and Honda V-TACS system. The result is an engine with better low-speed power without sacrificing high-speed power. However, as power valves are in the hot gas flow, they need regular maintenance to perform well. Direct injection has considerable advantages in two-stroke engines. In carburetted two-strokes, a major problem is a portion of the fuel/air mixture going directly out, unburned, through
2584-494: The first law of thermodynamics , the energy output cannot exceed the input, and by the second law of thermodynamics it cannot be equal in a non-ideal process, so 0 ≤ η t h < 1 {\displaystyle 0\leq \eta _{\rm {th}}<1} When expressed as a percentage, the thermal efficiency must be between 0% and 100%. Efficiency must be less than 100% because there are inefficiencies such as friction and heat loss that convert
2660-447: The ideal gas law . Real engines have many departures from ideal behavior that waste energy, reducing actual efficiencies below the theoretical values given above. Examples are: These factors may be accounted when analyzing thermodynamic cycles, however discussion of how to do so is outside the scope of this article. For a device that converts energy from another form into thermal energy (such as an electric heater, boiler, or furnace),
2736-473: The oil reservoir does not depend on gravity. A number of mainstream automobile manufacturers have used two-stroke engines in the past, including the Swedish Saab , German manufacturers DKW , Auto-Union , VEB Sachsenring Automobilwerke Zwickau , VEB Automobilwerk Eisenach , and VEB Fahrzeug- und Jagdwaffenwerk , and Polish manufacturers FSO and FSM . The Japanese manufacturers Suzuki and Subaru did
2812-528: The 1960s due in no small way to the increased power afforded by loop scavenging. An additional benefit of loop scavenging was the piston could be made nearly flat or slightly domed, which allowed the piston to be appreciably lighter and stronger, and consequently to tolerate higher engine speeds. The "flat top" piston also has better thermal properties and is less prone to uneven heating, expansion, piston seizures, dimensional changes, and compression losses. SAAB built 750- and 850-cc three-cylinder engines based on
2888-407: The 1960s, especially for motorcycles, but for smaller or slower engines using direct injection, the deflector piston can still be an acceptable approach. This method of scavenging uses carefully shaped and positioned transfer ports to direct the flow of fresh mixture toward the combustion chamber as it enters the cylinder. The fuel/air mixture strikes the cylinder head , then follows the curvature of
2964-499: The COP can be greater than 1 (100%). Therefore, heat pumps can be a more efficient way of heating than simply converting the input work into heat, as in an electric heater or furnace. Since they are heat engines, these devices are also limited by Carnot's theorem . The limiting value of the Carnot 'efficiency' for these processes, with the equality theoretically achievable only with an ideal 'reversible' cycle, is: The same device used between
3040-408: The COP of a heat pump is more than 1. These values are further restricted by the Carnot theorem . In general, energy conversion efficiency is the ratio between the useful output of a device and the input, in energy terms. For thermal efficiency, the input, Q i n {\displaystyle Q_{\rm {in}}} , to the device is heat , or the heat-content of a fuel that
3116-439: The Carnot efficiency. The Carnot cycle is reversible and thus represents the upper limit on efficiency of an engine cycle. Practical engine cycles are irreversible and thus have inherently lower efficiency than the Carnot efficiency when operated between the same temperatures T H {\displaystyle T_{\rm {H}}} and T C {\displaystyle T_{\rm {C}}} . One of
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3192-448: The German inventor of an early form in the mid-1920s, it became widely adopted in Germany country during the 1930s and spread further afield after World War II . Loop scavenging is the most common type of fuel/air mixture transfer used on modern two-stroke engines. Suzuki was one of the first manufacturers outside of Europe to adopt loop-scavenged, two-stroke engines. This operational feature
3268-528: The achieved COP to the Carnot COP, which can not exceed 100%. The 'thermal efficiency' is sometimes called the energy efficiency . In the United States, in everyday usage the SEER is the more common measure of energy efficiency for cooling devices, as well as for heat pumps when in their heating mode. For energy-conversion heating devices their peak steady-state thermal efficiency is often stated, e.g., 'this furnace
3344-395: The ambient temperature is T C = 21 ∘ C = 70 ∘ F = 294 K {\displaystyle T_{\rm {C}}=21^{\circ }{\text{C}}=70^{\circ }{\text{F}}=294{\text{K}}} , then its maximum possible efficiency is: It can be seen that since T C {\displaystyle T_{\rm {C}}}
3420-423: The bore diameter for reasonable piston ring life. Beyond this, the piston rings bulge into the exhaust port and wear quickly. A maximum 70% of bore width is possible in racing engines, where rings are changed every few races. Intake duration is between 120 and 160°. Transfer port time is set at a minimum of 26°. The strong, low-pressure pulse of a racing two-stroke expansion chamber can drop the pressure to -7 psi when
3496-443: The calculations of efficiency vary, but the non-dimensional input is still the same: Efficiency = Output energy / input energy. Heat engines transform thermal energy , or heat, Q in into mechanical energy , or work , W out . They cannot do this task perfectly, so some of the input heat energy is not converted into work, but is dissipated as waste heat Q out < 0 into the surroundings: The thermal efficiency of
3572-459: The combustion chamber, and then is deflected downward. This not only prevents the fuel/air mixture from traveling directly out the exhaust port, but also creates a swirling turbulence which improves combustion efficiency , power, and economy. Usually, a piston deflector is not required, so this approach has a distinct advantage over the cross-flow scheme (above). Often referred to as "Schnuerle" (or "Schnürle") loop scavenging after Adolf Schnürle,
3648-453: The crankshaft commonly spins in the same axis and direction as do the wheels i.e. "forward". Some of the considerations discussed here apply to four-stroke engines (which cannot reverse their direction of rotation without considerable modification), almost all of which spin forward, too. It is also useful to note that the "front" and "back" faces of the piston are - respectively - the exhaust port and intake port sides of it, and are not to do with
3724-415: The cycle's potential for high thermodynamic efficiency makes it ideal for diesel compression ignition engines operating in large, weight-insensitive applications, such as marine propulsion , railway locomotives , and electricity generation . In a two-stroke engine, the exhaust gases transfer less heat to the cooling system than a four-stroke, which means more energy to drive the piston, and if present,
3800-415: The efficiency with which they give off heat to the hot reservoir, COP heating ; refrigerators and air conditioners by the efficiency with which they take up heat from the cold space, COP cooling : The reason the term "coefficient of performance" is used instead of "efficiency" is that, since these devices are moving heat, not creating it, the amount of heat they move can be greater than the input work, so
3876-460: The energy into alternative forms. For example, a typical gasoline automobile engine operates at around 25% efficiency, and a large coal-fuelled electrical generating plant peaks at about 46%. However, advances in Formula 1 motorsport regulations have pushed teams to develop highly efficient power units which peak around 45–50% thermal efficiency. The largest diesel engine in the world peaks at 51.7%. In
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#17328586228373952-400: The engine from end loads. Large two-stroke ship diesels are sometimes made to be reversible. Like four-stroke ship engines (some of which are also reversible), they use mechanically operated valves, so require additional camshaft mechanisms. These engines use crossheads to eliminate sidethrust on the piston and isolate the under-piston space from the crankcase. On top of other considerations,
4028-415: The exhaust port in the cylinder, the hottest part of the engine, where piston lubrication is at its most marginal. The front face of the piston is also more vulnerable since the exhaust port, the largest in the engine, is in the front wall of the cylinder. Piston skirts and rings risk being extruded into this port, so having them pressing hardest on the opposite wall (where there are only the transfer ports in
4104-409: The exhaust port, and direct injection effectively eliminates this problem. Two systems are in use: low-pressure air-assisted injection and high-pressure injection. Since the fuel does not pass through the crankcase, a separate source of lubrication is needed. For the purpose of this discussion, it is convenient to think in motorcycle terms, where the exhaust pipe faces into the cooling air stream, and
4180-470: The factors determining efficiency is how heat is added to the working fluid in the cycle, and how it is removed. The Carnot cycle achieves maximum efficiency because all the heat is added to the working fluid at the maximum temperature T H {\displaystyle T_{\rm {H}}} , and removed at the minimum temperature T C {\displaystyle T_{\rm {C}}} . In contrast, in an internal combustion engine,
4256-413: The fresh intake charge into the upper part of the cylinder, pushing the residual exhaust gas down the other side of the deflector and out the exhaust port. The deflector increases the piston's weight and exposed surface area, and the fact that it makes piston cooling and achieving an effective combustion chamber shape more difficult is why this design has been largely superseded by uniflow scavenging after
4332-491: The fuel, but is generally close to the air value of 1.4. This standard value is usually used in the engine cycle equations below, and when this approximation is made the cycle is called an air-standard cycle . One should not confuse thermal efficiency with other efficiencies that are used when discussing engines. The above efficiency formulas are based on simple idealized mathematical models of engines, with no friction and working fluids that obey simple thermodynamic rules called
4408-444: The inherent irreversibility of the engine cycle they use. Thirdly, the nonideal behavior of real engines, such as mechanical friction and losses in the combustion process causes further efficiency losses. The second law of thermodynamics puts a fundamental limit on the thermal efficiency of all heat engines. Even an ideal, frictionless engine can't convert anywhere near 100% of its input heat into work. The limiting factors are
4484-741: The intake and exhaust (or scavenging ) functions occurring at the same time. Two-stroke engines often have a higher power-to-weight ratio than a four-stroke engine, since their power stroke occurs twice as often. Two-stroke engines can also have fewer moving parts , and thus be cheaper to manufacture and weigh less. In countries and regions with stringent emissions regulation, two-stroke engines have been phased out in automotive and motorcycle uses. In regions where regulations are less stringent, small displacement two-stroke engines remain popular in mopeds and motorcycles. They are also used in power tools such as chainsaws and leaf blowers . The first commercial two-stroke engine involving cylinder compression
4560-443: The intake and exhaust ports in some two-stroke designs can also allow some amount of unburned fuel vapors to exit in the exhaust stream. The high combustion temperatures of small, air-cooled engines may also produce NO x emissions. Two-stroke gasoline engines are preferred when mechanical simplicity, light weight, and high power-to-weight ratio are design priorities. By mixing oil with fuel, they can operate in any orientation as
4636-469: The model year. The Monte Carlo Rally variant, 750-cc (with a filled crankshaft for higher base compression), generated 65 hp. An 850-cc version was available in the 1966 SAAB Sport (a standard trim model in comparison to the deluxe trim of the Monte Carlo). Base compression comprises a portion of the overall compression ratio of a two-stroke engine. Work published at SAE in 2012 points that loop scavenging
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#17328586228374712-399: The oil pump of a modern two-stroke may not work in reverse, in which case the engine suffers oil starvation within a short time. Running a motorcycle engine backward is relatively easy to initiate, and in rare cases, can be triggered by a back-fire. It is not advisable. Model airplane engines with reed valves can be mounted in either tractor or pusher configuration without needing to change
4788-483: The other - the inlet pipe having passage to the crankcase only when the two cutouts coincide. The crankshaft itself may form one of the members, as in most glow-plug model engines. In another version, the crank disc is arranged to be a close-clearance fit in the crankcase, and is provided with a cutout that lines up with an inlet passage in the crankcase wall at the appropriate time, as in Vespa motor scooters. The advantage of
4864-434: The piston covering and uncovering the ports as it moves up and down in the cylinder. In the 1970s, Yamaha worked out some basic principles for this system. They found that, in general, widening an exhaust port increases the power by the same amount as raising the port, but the power band does not narrow as it does when the port is raised. However, a mechanical limit exists to the width of a single exhaust port, at about 62% of
4940-440: The piston is at bottom dead center, and the transfer ports nearly wide open. One of the reasons for high fuel consumption in two-strokes is that some of the incoming pressurized fuel-air mixture is forced across the top of the piston, where it has a cooling action, and straight out the exhaust pipe. An expansion chamber with a strong reverse pulse stops this outgoing flow. A fundamental difference from typical four-stroke engines
5016-550: The power band. Such valves are widely used in motorcycle, ATV, and marine outboard engines. The intake pathway is opened and closed by a rotating member. A familiar type sometimes seen on small motorcycles is a slotted disk attached to the crankshaft , which covers and uncovers an opening in the end of the crankcase, allowing charge to enter during one portion of the cycle (called a disc valve). Another form of rotary inlet valve used on two-stroke engines employs two cylindrical members with suitable cutouts arranged to rotate one within
5092-466: The principles remain the same, the mechanical details of various two-stroke engines differ depending on the type. The design types vary according to the method of introducing the charge to the cylinder, the method of scavenging the cylinder (exchanging burnt exhaust for fresh mixture) and the method of exhausting the cylinder. Piston port is the simplest of the designs and the most common in small two-stroke engines. All functions are controlled solely by
5168-544: The propeller. These motors are compression ignition, so no ignition timing issues and little difference between running forward and running backward are seen. Thermodynamic efficiency In thermodynamics , the thermal efficiency ( η t h {\displaystyle \eta _{\rm {th}}} ) is a dimensionless performance measure of a device that uses thermal energy , such as an internal combustion engine , steam turbine , steam engine , boiler , furnace , refrigerator , ACs etc. For
5244-806: The same in the 1970s. Production of two-stroke cars ended in the 1980s in the West, due to increasingly stringent regulation of air pollution . Eastern Bloc countries continued until around 1991, with the Trabant and Wartburg in East Germany. Two-stroke engines are still found in a variety of small propulsion applications, such as outboard motors , small on- and off-road motorcycles , mopeds , motor scooters , motorized bicycles , tuk-tuks , snowmobiles , go-karts , RC cars , ultralight and model airplanes. Particularly in developed countries, pollution regulations have meant that their use for many of these applications
5320-400: The same temperatures is more efficient when considered as a heat pump than when considered as a refrigerator since This is because when heating, the work used to run the device is converted to heat and adds to the desired effect, whereas if the desired effect is cooling the heat resulting from the input work is just an unwanted by-product. Sometimes, the term efficiency is used for the ratio of
5396-517: The temperature at which the heat enters the engine, T H {\displaystyle T_{\rm {H}}\,} , and the temperature of the environment into which the engine exhausts its waste heat, T C {\displaystyle T_{\rm {C}}\,} , measured in an absolute scale, such as the Kelvin or Rankine scale. From Carnot's theorem , for any engine working between these two temperatures: This limiting value
5472-418: The temperature of the fuel-air mixture in the cylinder is nowhere near its peak temperature as the fuel starts to burn, and only reaches the peak temperature as all the fuel is consumed, so the average temperature at which heat is added is lower, reducing efficiency. An important parameter in the efficiency of combustion engines is the specific heat ratio of the air-fuel mixture, γ . This varies somewhat with
5548-408: The thermal efficiency is where the Q {\displaystyle Q} quantities are heat-equivalent values. So, for a boiler that produces 210 kW (or 700,000 BTU/h) output for each 300 kW (or 1,000,000 BTU/h) heat-equivalent input, its thermal efficiency is 210/300 = 0.70, or 70%. This means that 30% of the energy is lost to the environment. An electric resistance heater has
5624-511: The top or bottom of the piston. Regular gasoline two-stroke engines can run backward for short periods and under light load with little problem, and this has been used to provide a reversing facility in microcars , such as the Messerschmitt KR200 , that lacked reverse gearing. Where the vehicle has electric starting, the motor is turned off and restarted backward by turning the key in the opposite direction. Two-stroke golf carts have used
5700-458: The useful energy produced worldwide is wasted in engine inefficiency, although modern cogeneration , combined cycle and energy recycling schemes are beginning to use this heat for other purposes. This inefficiency can be attributed to three causes. There is an overall theoretical limit to the efficiency of any heat engine due to temperature, called the Carnot efficiency. Second, specific types of engines have lower limits on their efficiency due to
5776-530: Was used in conjunction with the expansion chamber exhaust developed by German motorcycle manufacturer, MZ, and Walter Kaaden. Loop scavenging, disc valves, and expansion chambers worked in a highly coordinated way to significantly increase the power output of two-stroke engines, particularly from the Japanese manufacturers Suzuki, Yamaha, and Kawasaki. Suzuki and Yamaha enjoyed success in Grand Prix motorcycle racing in
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