Can someone explain, simply, the " Miller cycle" gas engine design?
Miller cycle gas engines
- Thread starter MAJA
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So, the "Miller cycle" can simply be described as modified valve timing, coupled with forced induction, to increase power through reduced friction losses, correct?
yeah i got miller wankel mixed up.
sorry about that folks!
Miller cycle gas engine is a "tricked" 4-cycle engine with supercharger. The tricking part involves intake/exhaust valve operlapping during the intake/exchaust stage ....*quite technical to explain*
In layman's terms: Miller-cycle engine is basically a tricked supercharged gas engine...
This engine has not only technical merits in modern day EFI engine designs but also historical perspectives as well.
The Miller Cycle that Mazda used is a V6. The way it works the intake valve is opened to let air and fuel in the exhaust valve is also opened for a period of time, just like a normal engine. As the piston starts its compression stroke the intake valve remains opened. This basically reduces the effective displacement of the engine as part of the compression volume is lost since the intake valve doesn't fully close until the piston is partially up the compression stroke. A supercharger is needed to work against the compression stroke of the piston while the intake valve is still opened. So you have an engine that equals 3 litres physically but in reality is 2.3 litres with a supercharger on it. There's a reason it was not very successful for Mazda.
When Mazda started advertising their 'Miller cycle", I found out what the cycle is and just started laughing.
Using the "expansion ratio is greater than the compression ratio" argument, and then supercharging it (which must be added to the compression part of the equation) is silly.
I think that it would be relatively easy to make any supercharged 2.3 engine out power a N.A. 3 litre...and get better economy at part throttle by virtue of being smaller.
quote:To increase power through increasing the density of the fuel/air charge in the cylinder.
Originally posted by MAJA: So, the "Miller cycle" can simply be described as modified valve timing, coupled with forced induction, to increase power through reduced friction losses, correct?
quote:I agree Shannow. In the mid nineties when Mazda came up with idea they had a great emgine in the 2.5 litre V6. Seems like they could have done a bit of tuning to an already succesfull design to bump up the power output a bit.
Originally posted by Shannow: When Mazda started advertising their 'Miller cycle", I found out what the cycle is and just started laughing. Using the "expansion ratio is greater than the compression ratio" argument, and then supercharging it (which must be added to the compression part of the equation) is silly. I think that it would be relatively easy to make any supercharged 2.3 engine out power a N.A. 3 litre...and get better economy at part throttle by virtue of being smaller.
quote:It's a modification of the traditional Otto 4-cycle in that the intake valves remain open longer than they would with only atmospheric pressure to charge the cylinder with the gas/air mixture. That additional duration allows additional gas/air to enter the cylinder. Ralph Miller patented his Miller-cycle engine in the 1940s. What you get is a high expansion ratio low compression ratio engine (due to the shortened duration of the compression stroke), lower pumping losses, and some reduction in both pre-ignition and nitrogen oxide. This engine was actually developed for the Amati line that was never introduced in the U.S. or Japan. Mazda spent several billion working on an Infinity/Lexus/Accura competitor line-up that finally bankrupted Mazda. Items salvaged from that attempt included the original Millenia and the Miller cycle engine.
thedawk: ..... The way it works the intake valve is opened to let air and fuel in the exhaust valve is also opened for a period of time, just like a normal engine. As the piston starts its compression stroke the intake valve remains opened. This basically reduces the effective displacement of the engine as part of the compression volume is lost since the intake valve doesn't fully close until the piston is partially up the compression stroke. .....
quote:They already did a bit of tuning. The International market 2.5L ("KL03") made 165bhp, the domestic, Japan-only 2.5L ("KLZE") made 200bhp. The only differences are higher compression, different intake manifold, slightly different heads and a different ECU.
Originally posted by thedawk: In the mid nineties when Mazda came up with idea they had a great emgine in the 2.5 litre V6. Seems like they could have done a bit of tuning to an already succesfull design to bump up the power output a bit.
they wobble like a spyrograph. intake, compression, bang, exhaust.
the cool thing is that while 1 rotor is doing 1 thing, like intake, it can also be doing somthing else, like exhaust. this is because a rotor has more than 1 side, so it can do more than 1 thing at a time. it then can do more at once per rotor than a piston can. a piston can only do 1 thing at a time because it only has 1 side.
quote:I think you're confusing a rotary engine with the Miller cycle engine, they are two very different things. The Miller cycle engine has no rotors in it that I'm aware of.
Originally posted by cryptokid: they wobble like a spyrograph. intake, compression, bang, exhaust. the cool thing is that while 1 rotor is doing 1 thing, like intake, it can also be doing somthing else, like exhaust. this is because a rotor has more than 1 side, so it can do more than 1 thing at a time. it then can do more at once per rotor than a piston can. a piston can only do 1 thing at a time because it only has 1 side.
Miller Cycle has been used on a lot of diesel engines for a long time!
JohnBrowning,
too right they have.
We've got a Mirlees straight 8 turbodiesel at workj for back-up generation.
Was commissioned in a sub in 1956 or thereabouts, served duty in Broken Hill, then ended up at a power station in 1975/6.
The manual shows the cam timing for the N.A. and the turbo versions.
Turbo cam timing looks very Miller cycle.
Crower Cams played with the Miller Cycle cam in the Maxi Mouse project in the '80's. Last year I contacted them to see if I could buy one of the cams for a build I was doing. Pimples (the kid on the phone) acted like he never heard of the concept/project and would not try to find out any info. on it.
A heated Smokey Ram would have provided a great place to hold the reversion and the heat would have helped the fuel from falling out of the mix.
KW,
once upon a time I had a concept of heating hydrocarbons and water vapour and passing them over a catalyst, and using the resultant gasses as a fuel.
Heat was to come from the waste heat of the process.
Later found out that "water gas" was produced similarly.
quote:I think Smokey Yunick (sp) had a similar idea that he toyed with. Dont remember his results, or the outcome of it, though.
Originally posted by Shannow: KW, once upon a time I had a concept of heating hydrocarbons and water vapour and passing them over a catalyst, and using the resultant gasses as a fuel. Heat was to come from the waste heat of the process. Later found out that "water gas" was produced similarly.
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