You'll understand everything about Atkinson, Miller and Otto cycle engines after watching this video

A typical four stroke engine or an Otto cycle engine does intake, compression, combustion and exhaust. The Atkinson cycle and the Miller cycle engines also do intake, compression, combustion and exhaust, however they differ in a small but very important detail which allows them to be significantly more efficient than the Otto combustion cycle. And in this video we will dive back into the history of engines in order to see and learn about the evolution of the combustion engine and the difference between four stroke Otto, Atkinson and Miller cycle engines .

The Otto engine as we know it today was invented in 1876 by German Nicolaus August Otto.
Although it doesn't seem that way the 1876 engine has many of the elements we see on engines today and is Otto's first true four stroke engine. There's a crankshaft, a connecting rod and even a camshaft. Inside we have a piston and the engine does intake, compression, combustion and exhaust just like any modern engine.

Of course Otto's first engine was an instant commercial success and of course Otto patented the design. Now this, the patent, is what brings us to Mr . James Atkinson, who like many of his contemporaries, after seeing the commercial success of the Otto engine, started developing his own engine. Now the catch is that in order to be commercially viable such an engine had to be different enough from Otto's design in order to not infringe on the patent rights.

Now Atkinson decided that the compression stroke of the Otto engine was actually something that could be improved upon, and that was to be done by reducing the length of the compression stroke in relation to the length of the combustion stroke, or the expansion stroke as some call it. In other words the engine would spend more time making power than wasting power on compressing the air fuel mixture.

In 1957 US engineer Ralph Miller patented the Miller Cycle engine. Now the Miller Cycle engine relies on the same concept as the Atkinson engine and that is to reduce the power sapping effects of the compression stroke. The big deal is that Ralph Miller chose a much simpler and much more elegant solution compared to the extremely complicated set of rods and linkages from Atkinson's original design.

And the solution is this: keep the intake valve open longer. That's it. The construction of the engine stays absolutely the same as that of a conventional Otto engine, the only thing that differs is the valve timing. A conventional Otto engine closes the intake valve before the compression stroke begins. This is done in order to ensure that the entire length of the cylinder is used to store and compress the air fuel mixture leading to optimal power output. The Miller engine doesn't close the intake valve when the compression stroke begins. The intake valve is kept open during the first 20-30% of the compression stroke. An open intake valve of course means that the upward motion of the piston simply pushes some of the air fuel mixture back into the intake manifold. The piston can't compress anything until the intake valve closes.

In fact in the late 90s Mazda put this exact concept into practice with their KJ-ZEM engine which they installed into the Mazda Millenia / Xedos 9 /Eunos 800. The KJ-ZEM was a supercharger 2.3 V6 running the Miller Cycle.

Right after the Mazda Millenia was discontinued Toyota revived the concept behind the Atkinson/Miller cycle. Toyota's foray into this field started in 1997 with the very first generation of the Toyota Prius and it's 1NZ-FXE engine. But this time instead of a supercharger we have an electric motor which is used to make up for the lack of torque and responsiveness. As we know electric motors produce instant torque and they don't sap the power of the engine like superchargers do which means that hybrid drivetrains and the Atkinson cycle are a match made in heaven which was put into practice in all of Toyota's hybrid vehicles. Now another advantage that modern technology has brought is variable valve timing or VVT. This makes it possible to run the engine in the Atkinson cycle only when this is desirable, which reduced load conditions such as highway cruising.

Now Toyota's usage of the Atkinson cycle is perhaps the most popular to date, but Mazda definitely hasn't given up and they employed the Miller cycle yet again in a fashion similar to what we have seen in the Mazda Millenia. This time it bears the name Skyactiv-X and in addition to a small roots supercharger and the Miller cycle the Skyactiv X is also the first ever commercial engine to have Spark Controlled Compression Ignition or SCCI.

A special thank you to my patrons:
Daniel
Pepe
Brian Alvarez
Peter Della Flora
Dave Westwood
Joe C
Zwoa Meda Beda
Toma Marini
Cole Philips

00:00 The road to compression
08:15 Atkinson
14:05 Miller
18:04 Mazda and Toyota

#d4a #atkinson #enginebootcamp

[seanlovi]

I can't believe am getting this education for free, it's almost illegal.

[chiefdenis]

I dont think I've ever seen a bad video from this guy, been here almost/roughly 3 years, and this guy is the GOAT of mechanical YouTube school, no one explains things quite like him, and I've seen everything.

[_monti]

i needed this video so much, nobody explains engines better than you on youtube, many thanks :D

[nathanaelvetters]

This is exactly what I needed. When I got my Prius, all I knew was "atkinson cycle more efficient less powerful" but was having trouble figuring out why or what the actual difference was. This explained everything and more. I think teaching engineering history is enormously helpful to explaining the concepts themselves.

[ozfugs]

This probably won't mean much to anyone else but I remember finding a Japanese guys personal university webpage back in the mid 1990's. I'm not sure if he was a professor or a student but it was like an encyclopedia for Japanese car technology of the time. He had excellent technical explanations and diagrams for all kinds of things. You could tell the guy loved the topic and loved sharing how it worked. That was part of my introduction to the Internet and even though the site is long gone I still have fond memories. And this channel reminds me of that. It's the same kind of intelligent and passionate effort. The same kind of enthusiasm. And it's cool to see how the delivery format has evolved from basic text to full on edited videos with 3d animations. I really enjoy this channel and appreciate the work that goes into it.

[hoganfan]

Good video. Ralph Miller’s original idea was to close the intake valve well before BDC to increase efficiency. He wrote about this (as I recall) in a 1948 ASME paper. I read his paper 25 years ago while working on VVL/VVT concepts for Chrysler. This works very well for low load efficiency (up to about 8% improvement), due to virtual elimination of the pumping loop by running unthrottled, and is what BMW Valvetronic and Fiat does Multi-air to run “unthrottled.”

A guy at GM named Don Stivender did research on extremely low lift cams in the 60’s, and another GM guy named Tuttle made very short duration cams (with more normal lifts) in the early ‘80’s, testing Miller’s original concept. Tuttle also ran very long duration cams to control load (testing the later miller approach) Stivender claimed a 5% improvement in efficiency, and Tuttle around 8%. Stivender called his very low lift the STIVE cycle (Sonic Throttling Intake Valve Engine). Very clever! I built some very short duration cams with moderately low lifts to verify the blended “Stivender & Tuttle/Miller” with the very early intake valve closing concept in our 1.6l “Tritec” engine in 1999/2000 and verified the concept could deliver about 6-8% lower BSFC unthrottled. Most folks (even engine guys) didn’t understand how this works, but the evidence is right in the P-V diagram, and the virtual elimination of the pumping loop. Here’s are links to Tuttle’s 1980 & ‘82 SAE papers(I couldn’t find Miller’s):



Here’s Stivender’s paper:

[jimosborn]

Excellent explanation. When I was learning I was taught efficiency is related to compression ratio. Later I discovered it is really a matter of expansion ratio. Atkinson/Miller cycles let you have an expansion ratio much larger than an Otto cycle.

[ishtiaquehussain]

Thanks a lot, man! You are unbelievably good at explaining complex engineering topics. Please know that we really really appreciate your channel, your videos and everything that you do for us. Wish you all the best for the future!

[thatguyonpoint]

Another great video. As a mechanical engineering student you've taught me way more than any class ever could!

[kristianhermann]

On efficiency, it's worth mentioning the added power with Otto allowed for engine downsizing too - so on a HP-to-HP basis, added efficiency with an Atkinson required a larger engine - awesome history lesson!

[-Jethro-]

I’ve always thought of this more as increasing the power stroke length to extract more usable energy, rather than decreasing the compression stroke. It’s really the same thing, but I believe it better expresses the intent of increasing efficiency.

Thanks for the video! Good stuff.

[jasperrodrigues]

Goodness GRAVY! You are unbelievably good at explaining and illustrating things. I can only imagine how much time and work you put into honing your skills and knowledge. Thank you so much for posting your videos and sharing your knowledge with the rest of us. - Jasper

[eTiMaGo]

I guess Toyota didn't want people to think "It's Miller time!" about their engines :D

Seriosuly though, thanks again, I knew the basic conceptual differences between these engine types, but you have brought me a new level of understanding :)

[reneneron]

Great video. Not all Toyota hybrids use the Atkinson cycle engine in their hybrids; the 3MZ hybrid engine does not. Further, Toyota will often increase the base compression ratio on an engine used in the Atkinson cycle model so that the effective compression ratio is similar to the Otto cycle version (an example being the hybrid 2AR-FXE versus the standard 2AR-FE). The camshaft profiles and valve timing are different as well. With proper engine management, the 2AR-FXE can be operated as an Otto cycle engine to gain power with a loss of efficiency with higher octane fuel. There is still a loss of power with the Atkinson cycle compensated for by the electric motor, but improved efficiency. Detonation (and octane) limits the practical compression ratio of any gasoline ICE engine.

[vmkkdt]

While browsing\watching automotive and car engineering videos and not looking for any otto, atkinson or miller proces details, I more or less came across this video by chance. Amazed! A very well made (entertaining) video explaining the principles, differences and last but not least the history of the otto, atkinson and miller processes and applications. A million thanks and thumbs up for driving4answers!

[jhaluska]

I have been enjoying the history and engineering lessons you provide on engines. It really helps me understand and appreciate them more.

[asharma]

Dude,

This is Excellent Video.

Full of Information.

[PaulThomas-qovy]

Thank you for the BEST comparative explanation of these 3 piston engine cycle types! Very clear & precise!

[KO-pkdf]

I have known of these engines for a long time but now I actually understand the difference between them! Thanks.

[ISHQEAMEEN]

This type of video i was waiting for
Thank you so much bro
Keep it up