The thermal efficiency of the Atkinson cycle will be more than the Otto cycle. The only question is the one I originally posed: Is this behavior adjusted for altitude. In simple terms, the Atkinson cycle was designed to minimise the use of fuel during the intake stroke yet exploit the part of the cycle that generates power. I know some cars have variable lift and other have variable duration of valve openings. The intake air is first compressed by the supercharger and then cooled by an.
This allows more work to be extracted from the expanding gases as they are expanded to almost atmospheric pressure. Pumping work is the difference between the work done during exhaust stroke and the work done during intake stroke. On the intake stroke, the piston doesn't move all the way down the cylinder. The black arc is the exhaust timing and duration, which is fixed. The final return stroke of the cycle evacuates the spent gases via the exhaust valve so that the process can begin again. Using an electric motor to assist the petrol engine addressed the shortfall of power characteristic of the Atkinson cycle, but also provided an independent source of motivation in order that the engine could be shut off when possible.
This forms the basis of an Atkinson cycle-based drivetrain. But the uneven strokes of the piston in his -powered combustion engine fit our modern hybrid systems pretty neatly. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed. This modification of the Atkinson cycle allows the use of alternative fuels such as diesel and hydrogen. Battery-fed electric motors were used to assist the petrol engine when necessary but also provide an independent source of motivation. But in order to understand where we're at today, we first have to know where we've been.
After all, the most effective method of fuel-saving is not to have the engine running in the first place! While originally seen exclusively in applications such as the earlier-generation , later hybrids and some non-hybrid vehicles now feature engines with , which can run in the Atkinson cycle as a part-time operating regimen, giving good economy while running in Atkinson cycle, and conventional power density when running as a conventional, engine. The pressure-charger shown in the diagrams is a , not a positive-displacement supercharger. See below for more information. But even with a symmetrical timing, at low speed if the opening duration is long, a reversion of the fresh charge into the intake ducts also happens; the volumetric ratio can then be increased because the effective compression ratio is thus reduced precisely where the pre-ignition and detonation propensity is the strongest. Typically, this loss of charge air would result in a loss of power.
Modern Atkinson-cycle engines do away with this complex energy path. So in the Miller cycle engine, the piston actually compresses the fuel-air mixture only during the latter 70% to 80% of the compression stroke. Compression does not actually begin until this point, effectively shortening the compression stroke to match the shortened intake stroke. The cycle begins with a downward piston stroke, which draws a mixture of air and vapourised fuel through the intake valve opening into the combustion chamber. The payoff comes after ignition when the piston begins descending on the expansion also called power stroke. Atkinson wins on efficiency because its expansion ratio is significantly larger than its compression ratio.
Thus, in each revolution, one piston provided a compression stroke and a power stroke, and then the other piston provided an exhaust stroke and a charging stroke. While Atkinson deserves credit for perhaps being the first to recognize the benefits of having different compression and expansion ratios, Miller should be credited for devising a recipe for achieving a set of objectives that remains relevant even to modern internal combustion engines. Most spark ignition engines since the dawn of motoring have employed a four-stroke thermodynamic cycle developed in the late 19th Century by a German engineer named Nikolaus Otto. The goal of the modern Atkinson cycle is to make the pressure in the combustion chamber at the end of the power stroke equal to atmospheric pressure. In the latter example, the particular nature of the Miller cycle permits the supercharged version to not only be moderately more powerful, but also claim better, almost diesel-like fuel economy with lower emissions than the simpler, cheaper suction-intake one - in contrast to the usual situation of supercharging causing significantly increased fuel consumption. However since less work was expended during the compression stroke, overall efficiency may be increased.
My illustration shows only an exhaust cam. The effect is to produce an engine with a. The force sends the piston back down the shaft of the cylinder in the power stroke, this time all the way down to take advantage of every last bit of force generated by the combustion. Due to a smaller portion of the compression stroke being devoted to compressing the intake air, an Atkinson-cycle engine does not take in as much air as would a similarly designed and sized Otto-cycle engine. The efficiency results in the 1.
The disadvantage of the four-stroke Atkinson-cycle engine versus the more common Otto-cycle engine is reduced power density. The British patent is from 1892, 2492. Atkinson's third and final engine, the utilite engine, operated much like any two-stroke engine. The expansion ratio of a conventional reciprocating engine is determined by the kinematics its crank drive mechanism, which implies identical geometric expansion and compression strokes. There is no definite limit in response to this question, which in fact amounts to asking at which age an animal is old, at what height a tree is tall or what is the temperature limit between warm and cold! During the initial part of the compression stroke, the piston pushes part of the fuel-air mixture through the still-open intake valve, and back into the intake manifold. After the exhaust port is covered the piston begins to compress the remaining air in the cylinder.
You are correct that they both hold the intake valve open for a longer period, but there is a difference. Though effective and incredibly clever, the design was not cost-effective for mass production. It was adapted by for their , used in the sedan, and in their Eunos 800 sedan Australia luxury cars. The Otto Cycle Four-stroke engines have four separate phases within a traditional Otto cycle, produced by two revolutions of the crankshaft and precise valve and ignition timing. Even though the piston is allowed to travel further down on the power stroke than it does on the intake stroke, it's not going to generate as much power as it does in an engine with higher compression and a richer gas mixture. I really noticed it when driving my manual transmission cars high up in Colorado. About 15 to 20% of the power generated by a supercharged engine is usually required to do the work of driving the supercharger, which compresses the intake charge also known as boost.
Compression and expansion ratios are the same in an Otto engine. For example, it is 8:1. The Isentropic Expansion of this Otto cycle is further allowed to proceed to the lowest cycle pressure in order to increase the work output. In reality, the ideal cycle does not occur and there are many losses associated with each process. His cycle was intended for use with two- and four-stroke engines running on gasoline, diesel, or gaseous fuels such as propane.