• Aug 11, 2009
English engineering firm Ilmor knows all about engine design, having produced powerplants for Formula One, IndyCar, and NASCAR. But its latest internal combustion creation, in contrast to those racing engines, is designed to burn fuel more frugally: a gas-powered five-stroke with diesel consumption.

It starts with a three-cylinder, 700cc, turbocharged engine with 130 hp and 122 lb-ft. There are two overhead camshafts: a high pressure shaft turning at half the crank speed working on the two high pressure cylinders, and a low pressure shaft running at crank speed for the third cylinder. The two outside, high-pressure cylinders work like a normal four-stroke, but alternate their exhaust flow into the third, central low-pressure chamber. That cylinder's expansion and compression strokes aren't fixed, so it can be selectively tuned for the best expansion ratio.

The principle is that extra work gets done for the same amount of gas, and Ilmor claims increased fuel efficiency over conventional gas engines. The five-stroke is made with current, in-use technology so there'd be no extra costs for exotic materials or processes, and it's said to be "relatively compact." Ilmor says the next step is to build another working prototype with targets of 10 less engine weight compared to an equivalent four-stroke engine.

[Source: Ilmor via Motor Authority]


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    • 1 Second Ago
  • 38 Comments
      luvmybeama
      • 4 Months Ago

      The Herreshoff Manufacturing Company, the largest yacht builders in the country (and maybe the world) prior to WW II, built and tested a compound-expansion (5 cycle) gasoline engine more than a hundred years ago. It had overheating problems so it was not developed commercially. It can still be seen at the Herreshoff Museum in Bristol, RI.

      • 5 Years Ago
      This is similar to what has been being done with turbines for quite some time - utilize the "waste heat" from the first expansion process in a lower pressure system.

      The fifth "stroke" is effectively the introduction of the exhaust gas through the center piston.
      • 5 Years Ago
      suddenly BMW's 3-series with 3-cylinder engines don't sound so far-fetched.
      • 5 Years Ago
      Did I just see super-100 hp, super-100 lb-ft numbers from a sub-1 L, sub-4 cylinder engine?
      Holy engineering Batman!
      • 5 Years Ago
      The number of prototype ICEs never ceases to amaze me. It will just become a matter of making a large-scale business justification and you'll start seeing many more alternative-cycle engines on the market (quasi-turbine, etc.)
      Prasanta Kundu
      • 2 Years Ago
      its amazing to world automobile industries.....i'm really surprised............
      • 5 Years Ago
      Mercedes was buying their Formula 1 engines, maybe they will also buy this design from Ilmor.
      • 5 Years Ago
      Well, that would be 185hp 174tq per liter. So a 5.0L V8 might be producing around 925hp 875tq? Those numbers are impressive for a diesel motor, especially in its infant stage of development!

      I understand a 5.0L V8 probably might not make that kind of power, but I just posted it for comparison to the 3 cylinder. Hopefully it can come to fruition and with better fuel economy figures. A few extra MPG is not going to be enough for manufacturers to adopt. It'd probably be cheaper to turbocharge a smaller engine, but I might be wrong.
      • 5 Years Ago
      Just 10% better fuel efficiency? That doesn't seem like a big enough increase to me... wouldn't it be simpler and more effective to just develop diesel engines further?
        • 5 Years Ago
        @Tourian

        You can't make a 4 cyl design with this far as I can see unless you route 3 smaller pistons' exhaust all into one big cylinder. I don't think there's the valve space for it to work terribly well, plus all the heat energy lost during routing of the exhaust just leaves via the radiator. So that means less efficiency and probably a minimal power increase despite the extra piston. Basically, to make a super clean I4 equivalent would mean making a V6 which is a big issue since space is at a premium for small cars.
          luvmybeama
          • 4 Months Ago

          You can make a 4 cylinder design, the large center cylinder of the 3 cylinder engine is replaced by two normal sized cylinders. The path length from the outer, active cylinders to the expansion cylinder that is farthest away gets a little long, resulting in losses.

        • 5 Years Ago
        But look at the power, that's only 700cc and 3 cylinders. What if it were 2.0L/2.4L and (3)/4 cylinders like a typical small car engine?
      • 5 Years Ago
      Engineers amaze me.
        • 5 Years Ago
        And that's exactly how I feel and why I tend to banish the pencil necks from my lab or the floor.
        • 5 Years Ago
        @lets

        "all they need is a problem to solve" - AND for everyone to stay out of their why while they solve it.
        • 5 Years Ago
        All an engineer needs is a problem to solve. Their capacity for creative thought is a boon to all mankind.

        Hey, if it keeps the ICE around that much longer, I'd be happy!
      • 5 Years Ago
      http://paultan.org/2006/03/14/bruce-crowers-6-stroke-crower-cycle-engine/

      I read this in PopSci a few years ago. Basically, this guy (also a former race engineer) takes a regular 4 stroke and right after the exhaust stroke, water would be injected into the hot cylinder. This would create a second power stroke with high pressure steam with no additional fuel. It also has the added benefit of cooling the engine from the inside as well as reducing knocking from forced induction and high compression applicatons. Rather brilliant concept. 40% more efficiency and a lot of weight reduction due to the cooling effect.
        • 5 Years Ago
        @Noah, it wasn't a big breaktrought, but mazda also use the miller cycle engine back in the 90's.
        • 5 Years Ago
        I wonder how much water the car would have to carry to match a tank of gas? I like that idea too. A free powerstroke.

        I agree with another poster above, seeing new ideas for the ICE engine. I wonder why its always been just the reciprocating piston engine that has been used (well, the rotary to a very small extent), and only OHV and OHC the main difference. How come we haven't seen greater variety in ICE? Opposed pistion engines, quasi-turbine, etc.? There are so many ways to make ICE better, yet we've only improved on reciprocating pistons, and then most of the variety there has to do with the camshafts.
      • 5 Years Ago
      I seem to recall steam engines in ships that used the steam three times in progressively larger cylinders.
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