Holding the valve open for a longer period allows more time to push more air and fuel into the chamber. During the compression stroke in an Otto cycle engine, the intake valve is closed as the piston compresses the fuel-air mixture against the cylinder wall. This type of engine was first used in ships and stationary power-generating plant, but has recently late 1990s been adapted by Mazda for use in the Mazda Millennia which is also known as a Eunos 800 in some countries. Pictured above; The Mazda Millenia Find great prices on similar books below In engineering, the Miller cycle is a combustion process used in a type of four-stroke internal combustion engine. The Miller cycle has the same four strokes intake, compression, power, exhaust with one key difference. The best mechanic in town and now the Mazda dealer have been unable to fix.
Using a higher octane fuel would in this case make combustion more difficult. With this new engine, however, Mazda further cements its reputation as an automaker with a penchant for alternative forms of internal combustion. Eventually there will be some type of convergence between diesel and gasoline engines, with the ultimate goal to bring homogeneous charge compression ignition into the equation. The auto maker says it has about 150 patents on every detail of what makes its Skyactiv engine work. Miller cycle has been implemented in both diesel and gasoline engines. Production for the Millenia ended in 2002, without replacement.
Delaying the closing of the intake valve in the Miller cycle in effect shortens the compression stroke compared to the expansion stroke. Our top priority is to radically improve this technology. Mazda is doing something nearly every auto-manufacturer has thought about, researched, and certainly desired, but they did it all with the help of a spark plug. It was also sold as a Eunos 800 in Australia, as both the 800M, with the Miller Cycle engine and the base 800, with the 2. The Miller cycle engine has a compression ratio of around 14:1.
Occasionally, engines with late intake valve closings are referred to as Atkinson cycle engines. This includes the ongoing desire to create captivating design, to provide our customers with continual driving pleasure and to develop improved safety and environmental technologies. The Millenia was available in the U. The idea is to leave the intake valve open for a portion of the compression stroke, pushing some of the air and fuel out of the cylinder back where it came from. In a typical Spark Ignition Engine however the miller cycle yields another benefit. Ralph Miller patented his Miller-cycle engine in the 1940s, and for the last several years Mazda has been using this type of engine in some of its cars.
The engine may be or and may be run on , gases, or dual fuel. However, multiple tradeoffs on boosting system efficiency and friction due to the larger displacement need to be balanced for every application. Because the stroke is limited to that of the compression, still some work could be extracted from the gas. The piston gets all the compression for 70% of the work. With clever balancing of these compromises, overall fuel efficiency can be increased over the conventional Otto cycle. This includes the ongoing desire to create captivating design, to provide our customers with continual driving pleasure and to develop improved safety and environmental technologies. The car was launched in in 1995 as the Mazda Millenia and in July 1997 the market Eunos 800 was also renamed to Mazda Millenia as Mazda discontinued the brand.
The name implies a unique operating cycle that, in essence, is like variable valve timing in reverse. 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. However since less work was expended during the compression stroke, overall efficiency may be increased. The Miller cycle engine solves this problem by using forced induction typically a Roots-style supercharger to maintain compression while increasing the expansion ratio, or the rate at which the fuel-air mixture expands after ignition. Or perhaps you could think of intake tract resonance as a very simple form of supercharger. Since residual exhaust gas is very hot, even a small amount will dramatically increase the temperature in the cylinder. The rich mixture adjacent to the spark plug gets started, and the ball of burning fuel ignites the lean mixture, Coleman says.
In the Miller-cycle engine, the piston begins to compress the fuel-air mixture only after the intake valve closes; and the intake valve closes after the piston has traveled a certain distance above its bottom-most position: around 20 to 30% of the total piston travel of this upward stroke. This type of engine was first used in ships and stationary power-generating plants, and is now used for some railway locomotives such as the. The Atkinson cycle engine holds the intake valve open during a portion of the piston's rise, so that instead of compressing the entire intake charge, some of the charge is blown back out. The key, however, is that at low compressions the supercharger is better than the piston. The less lean area of air near the plug combusts, creating a tiny expanding flame front. It was a long time ago but the 14:1 kinda stuck in my mind since most engines at that time were about 8:1. During the compression stroke, the piston moves upward towards the cylinder head, increasing the pressure, and consequently the temperature, of the air-fuel mixture contained within.
The pressure-charger shown in the diagrams is a , not a positive-displacement supercharger. The main drawback to the Atkinson cycle engine is that the lower compression ratio makes it less powerful than an Otto cycle engine. 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. The pressure raises so high, and the temperature gets so hot, that even without a spark plug the vaporized gasoline combusts as the piston nears the top of its stroke. In other words the compression stroke is only 70 to 80% as long as the physical motion of the piston. In fact, it was the first mass-produced passenger car engine to run on the Miller cycle.
But since the combustion chamber volume is getting smaller while the piston is rising up, a supercharger is required to keep the air-fuel mixture flowing into the chamber. 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. Many of these early applications were motivated by the potential for increased power density and efficiency. It seems like the guy who designed it made his first engine out of a Chevy small block. When full power is desired, the duration of the intake valve's opening can be a limiting factor. The basic idea stems from attempting to accomplish the ideal engine: instantaneous combustion, no heat losses, and zero friction.
In the press release after the jump, Mazda makes a big deal about how efficient its new Miller engine is, but fails to mention how much power it makes. Thus the Miller cycle uses the supercharger for the portion of the compression where it is best, and the piston for the portion where it is best. Having been developed for a separate market from typical Mazda customers, the Millenia boasted myriad finer details. Higher expansion ratios capture more combustion energy, a fundamental engine characteristic. Other key technologies include direct multi-hole gas injection, dual variable-valve timing, new-design pistons, shorter combustion duration and delayed ignition during startup. If we can lower the temperature of the fresh-air charge enough, we can raise compression a calculable amount.