Why Five Stroke Engines Are More Efficient But Still a Failure

driving 4 answers
driving 4 answers
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Published 2024-06-23
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As you probably know internal combustion engines are not very efficient. On average modern gasoline engines in passenger cars manage around 35% whereas diesel versions can do a bit above 40% but need complicated and expensive emissions control equipment to be as clean as their gasoline counterparts.

An efficiency of 35% means that of the energy present in the fuel only 35% gets converted into useful work. The rest is lost. Some of it is lost to internal friction but most of it actually escapes as heat and noise out through the exhaust.

So why is so much energy lost? Why can’t we efficiently harness more of it?

The problem we have here is that all four strokes of a four stroke engine are of equal length and duration and of those four strokes it is only the combustion stroke that produces significant energy. The remaining three strokes mostly just consume energy. This means that an engine would be more efficient if it was given more time to actually harness the energy.

One of the ways to increase engine efficiency is to increase the compression ratio of an engine. A compression ratio is simply the ratio between the smallest and largest cylinder volume. But the positive effects of increasing the compression ratio are limited because we are limited in the amount of how much we can increase it. At some point space for combustion becomes so small that combustion occurs so close to the piston that too much energy is transferred too quickly which makes it hard for even the most robust engines to handle these shocks.

So we are limited in what we can do with the compression ratio. That means that we must look for other ways to increase efficiency the ideal thing to do would be to make the strokes unequal. What we actually want to do is have the combustion aka the expansion stroke somehow be longer than the other strokes.

Of course, the conventional rotating assembly does not permit different lengths for different strokes which is why James Atkinson decided to forego the traditional engine anatomy and created a new different engine anatomy that enabled the engine to have a noticeably longer combustion or expansion stroke. Even the inventor of the of the four stroke engine himself Nikolaus Otto saw the limits of his design and wanted to increase the time and space for the expansion and energy harnessing but Otto together with Gottlieb Daimler decided to take a different approach. Instead of creating a novel and unproven rotating assembly they decided to rely on existing engine anatomy. They simply added another cylinder to harness the remaining energy of the exhaust gas.

Instead of letting exhaust gas go out into the atmosphere the high pressure cylinders would send it into the low pressure cylinder where the pressure remaining in the exhaust gas was used to drive the larger middle piston. So the outer cylinders operate like normal four stroke cylinders.

Well all of that sounds great in theory but Otto and Gottlieb’s five stroke engine was a failure. It was commercialized but it suffered from poor performance and production was quickly discontinued. Probably because Gottlieb and Otto were working with technology from late 1800s.

And so the design was abandoned but not forgotten. It laid dormant for 124 years until 2003, when it was awakened by Belgian engineer and inventor Gerhard Schmitz who patented a three-cylinder five-stoke engine which was virtually identical to Otto and Daimler’s design.

Of course getting a patent for a theoretical concept is one thing. Getting that concept materialized into a working prototype is another. But here Gerhard Schmitz managed to convince a very serious company to turn his idea into reality. Ilmor engineering. Maybe you haven’t heard of them but Ilmor is nothing like any the newly sprung-up companies created around novel engine designs. Founded in 1983 by Mario Illien and Paul Morgan Ilmor engineering has been successfully designing and developing engines for Chevrolet in Indycar racing, for Sauber and Mclaren in Formula 1, they even competed in MotoGP.

So when a company like this takes on the development of a novel engine design it definitely gives the design credibility and high hopes of reaching mass production. So Ilmor got busy and just 4 years later in 2007, we got a running prototype.

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#d4a #fivestroke
All Comments (21)
  • @CaseyW491
    Driving 4 Answers manages to make videos on engine topics I've never heard of with pretty regular frequency. That's so rare on YouTube and I love it.
  • @ssattanen
    Hello from finland. I am mechanical engineer, and I most love your clear explanations and great videos. Most of things are clear for me, but you still can educate me. I am more than happy to learn from you. For example the EGR: I never thought about “dirtyness” in intake manifold caused by piston rings! As you explained it, it was completely clear. Of course Your videos are most relaxing and professional and clear as far as I know. Excellent work!
  • @justcarcrazy
    5:07 Diesel engines don't rev as high because of the flame propagation speed in the cylinder, not because of heavier internals. Top fuel dragster engines rev plenty high, yet they too have heavy internals to cope with the boost pressures.
  • @terryuland6502
    Sounds like a generator operated at a constant load and RPM would be a better use for the modern 5-stroke engine than a passenger car.
  • @russpayne6808
    This video is spot-on : a really good explanation of the basics, but also some deeper knowledge that is needed to really understand why these "improvements" on the basi cycle never got anywhere. I love the final teaser comments around "what would Otto say about his invention today?" .....I think he would be crushingly proud of that contribution, and in the same way that Mozart would play synthesizers, Otto would really appreciate variable valve-timing, turbos, fully digital control systems etc. Well done!
  • @fisharmor
    It wasn't abandoned - I instantly recognized this as a double expansion engine and steam engines in ships were using even triple expansion engines for decades until they got replaced with diesels.
  • @rightwingsafetysquad9872
    When I was in college in 2014, a group of 3 of us did a feasibility sudy on this concept. We determined that there was no design goal for which a 6-stroke engine was the optimum solution (terminology we used, but it was the same thing). If power density was desired, a bigger conventional engine is the best choice. If efficiency is desired, a turbocharger or turbine generator (for a hybrid system) on a smaller engine is best. It's a very interesting concept and has the potential to do what proponents claim. But it's just not better than alternatives.
  • @paulalcock6735
    Bro my Captions said Sad vacuum cleaner noises when he revved the car.
  • @tsbrownie
    17:50 Letting you know... steam turbine technology is just a few years behind ICEs having been invented in 1884. Electric motors were invented in 1832, so they are 192 years old. ;)
  • @alexguest9937
    Makes me think the best 'enhancement' of the 4 stroke engine ever designed was actually Honda's Variable Valve Timing. Rather than 're-inventing the wheel', Honda very wisely took one single aspect of it and applied new thinking (and technology) to produce something genuinely useful. Honda truly is a visionary company.
  • @toyotaprius79
    Just call it what it is, a compound engine. Steam cars, tractors and locomotives used it the most.
  • @OutsideTheTargetDemographic
    I come to this channel for the wrinkles in my brain, but I stay for the delicious diatribes you close the videos out with. 😂 "Don't tell me ICE is dead : Read the room!"
  • @barry7608
    For me an extremely interesting and very well presented video. My father was an aero engineer with RR and DeHavilland, back in war WW1 he was among the first to join the Royal Flying Corps. As a youngster he taught me much about 2 and 4 stroke engines but alas as my feisty years approached ‘life’ took a greater part and so much of what he knew was last. But whenever I would tell him about new advances, at least new to me, he would reply it’s all been tried before !! And he would tell me who where and why it failed, or was successful in some cases. I am eternally indebted to him for his efforts, but I think we may have missed the 5 stroke, but I’ll also bet he knew of the process. Thanks again I will forward to my son, take care
  • @MaximumBan
    *Harnessing the Power of Exhaust Gases: Balancing Efficiency and Emissions* In the quest for more efficient automotive engines, engineers continually seek ways to extract every possible bit of energy from the combustion process. One promising approach involves harnessing the power of exhaust gases, a strategy that, while potentially very effective, must be carefully balanced to maintain emissions standards. *Understanding the Ideal Gas Law* To appreciate the challenges and opportunities in harnessing exhaust gases, it's useful to revisit the ideal gas law: PV = nRT. In this equation, P represents pressure, V represents volume, n is the amount of gas, R is the gas constant, and T is the temperature. This relationship highlights that in a given volume, a reduction in pressure results in a decrease in temperature. This principle is critical when considering the use of exhaust gases to generate additional power. *Turbocharging and Turbines* One well-known method of utilizing exhaust gases is the turbocharger. Turbochargers use the exhaust gases to drive a turbine connected to a compressor, which then increases the pressure of the air entering the engine. This increased air pressure allows for more fuel to be burned, resulting in more power from the same engine displacement. However, turbocharging must be carefully managed to ensure that the exhaust gases remain hot enough to keep the catalytic converter functioning effectively. Another concept involves placing a turbine in the exhaust stream, similar to a turbocharger but designed to directly generate mechanical or electrical power from the exhaust gases. This approach can potentially convert a greater portion of the exhaust energy into useful work, but it also poses challenges. As exhaust gases expand through the turbine, their pressure drops, which according to the ideal gas law, also causes a drop in temperature. *Balancing Efficiency and Emissions* The challenge with using exhaust turbines lies in balancing the need to extract energy from the exhaust gases with the necessity of maintaining sufficient temperature for the catalytic converter. If the exhaust gases cool too much before reaching the catalytic converter, the converter's effectiveness in reducing harmful emissions such as CO and NOx is compromised. One potential solution is to carefully manage the design and placement of the turbine. By optimizing the turbine's efficiency and controlling the flow of exhaust gases, it may be possible to harness significant power without excessively reducing the gas temperature. Additionally, advances in materials and catalytic converter design could allow these components to operate effectively at lower temperatures, providing more flexibility in how exhaust energy is utilized. *Conclusion* Harnessing the power of exhaust gases represents a significant opportunity for improving engine efficiency and reducing fuel consumption. However, this approach requires a delicate balance to ensure that emissions control systems, particularly catalytic converters, continue to operate effectively. As automotive technology continues to advance, innovative solutions will be needed to maximize the benefits of exhaust energy recovery while maintaining strict emissions standards. By carefully managing the interplay of pressure, temperature, and catalytic reaction dynamics, engineers can unlock new levels of efficiency and performance in modern engines.
  • @petergerdes1094
    The Porsche approach of just using a turbine to turn the energy in the exhaust gas into electricity seems better. That approach naturally deals with the fluctuations and turbines are a well developed low weight way to harness energy.
  • @artysanmobile
    “..read—the—room!” What perfect delivery of that old chestnut. 👏🏽
  • @LJSpit
    Great show. Informative and entertaining. Hard to get both. And you do it!