• Jan 22nd 2010 at 7:00PM
  • 25
Omnivore [(om-nuh-vawr)]: An animal whose normal diet includes both plants and animals. Human beings and bears, for instance, are omnivores.

So says Dictionary.com, at least. Ask the engineering boffins from Lotus, though, and they'll tell you than an Omnivore is an engine that can operate on just about any combination of gasoline or alcohol at equally optimum efficiency and power. An impressive feat, to say the least. But how does it all work?

As they say, a picture is worth a thousand words. So far, we've used nearly a hundred of 'em and we haven't even touched the surface on how Lotus' Omnivore engine works. That said, we highly suggest you take a gander at the firm's very own Flash animation of the process, which allows you to make all sorts of cool adjustments to see how it impacts the operation of the powerplant. Cool stuff. Thanks for the tip, Chris!

[Source: Group Lotus]

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    • 1 Second Ago
      • 5 Years Ago
      Am I the only person here who feels that every performance manufacturer should release one of these animations with each new engine? It would be awesome.
      • 5 Years Ago
      Hey if it really works ill take a car with one.
      • 5 Years Ago
      Yes, what I'm looking for is a really complex piece of British machinery, please.
        • 5 Years Ago
        Yep. Very complex, but also very cool.

        I wonder how much efficiency this thing gives up compared to a conventional I-6 burning pump gas.
        • 5 Years Ago
        Well its just as well we british are working on modern engine technology.

        Leave it up to the USA and what do you get? The Mustang with a big old pushrod engine and leaf springs. Yep thats progress...
      • 5 Years Ago
      1:Anyone who knows Corvair engines knows that O-rings don't stand high temps for long, even the Viton ones, rated at only 400 degrees F.
      2:There's about 30% less energy in alcohol than gasoline, so the efficiency has to be different depending on which is used.
      3:It's British
        • 5 Years Ago
        Higher compression means higher loads and temps in the combustion chamber. This means heavier components within similar cost restraints. More weight=less efficient overall. This rig must be built to use any fuel, so the elegance is partially wasted using lower grades of gasoline. Higher test grades are more expensive, therefor perhaps less efficient overall. Stationary engines don't have to be concerned with weight. Every vehicle must weigh as little as possible to be be efficient. Adding weight underhood means more weight to support it in the chassis, thus less efficient.
        And two stroke engines have been bigger polluters, meaning more sophisticated and expensive downstream controls. Less efficient, again.
        It's tragic that the best engine around only gets half the use of its fuel.
        • 5 Years Ago
        Please read my post further down... Diesel engines are inherently more efficient than gasoline engines simply because they have higher compression ratios. The higher weight only has a marginal effect on efficiency (it does have considerable effect on responsiveness though).
        I worked on the worlds largest engine (with the heaviest components) and that is just about the most efficient engine you will ever find (49% total thermal efficiency without waste heat recovery, 53% with WHR). Efficiency does not depend on weight, but on friction - and if you can keep your oil film going, friction isn't a problem (and it doesn't depend on weight either).

        The big thing here is whether they are going to be able to make the compression shift plunger reliable enough, but I'm not worried that they will. It is a slow moving component, and if they can make an engine which can revolve at 6-7000 RPM, they should be able to produce a plunger which moves once or twice a second...
        • 5 Years Ago
        This is the biggest problem with developing a two-stroke for cars - peoples' attitude towards them as being dirty fart machines!

        The reason why two-strokes WERE more pollutive was because of the fuel being mixed with air before injecting. This resulted in unburnt fuel in the exhaust. Furthermore, you had lub oil in the gasoline which gave a very "dirty" burn - hence the pollution.

        Now, this engine has no fuel in the intake air, and it has a regular lubrication system - thus eliminating both emission issues. Actually, as the engine is far more efficient than a regular four-stroke, it will be much cleaner. If they can achieve an efficiency around the 40% mark, it will reduce it's emmision compared to gasoline engine by more than a third. And since you have a better thermal efficiency, the burn will be cooler and you'll have less NOx too...

        As to weight, don't forget that thought the components have to be heavier, the effective output will be a third higher than a comparable gasoline engine, so you can make the engine a third smaller with the same output. So the question is: will this engine weigh 33% more than a comparable gasoline engine - I don't think so! So it will be smaller and lighter thus further increasing fuel efficiency!
        • 5 Years Ago
        1. I just sold my last Corvair; been under and around them for decades, won't flog another one.
        2. The most common alcohol available is ethanol. Doubtful you'd see much grain or other corrosive racing fuels . The corn lobby's too tight to use anything else, and even with tax subsidies, farmed alcohol's an energy wash.
        3. They didn't teach about rocks in engineering school. I have been accused of having lead elsewhere.
        • 5 Years Ago
        1. The Corvair is a dead horse. Stop flogging it.

        2. Which alcohol are you talking about? Different alcohols, different energy content. Some of them *way* higher than similar weights of petroleum.

        3. That must be a nice rock you're living under.
        • 5 Years Ago
        Hope you're right. Taking the oil out of the mixture would eliminate the coking that has plagued two-stroke ports. Direct injection has to be better than reed valves, eliminating valve trains and their many parts. Excellent.
        • 5 Years Ago
        If you can change the effective compression ratio depending on the fuel somehow, it's worth a try. That would be really cool. Or hot. Added compression means heavier components (think diesel), all of which add weight and lessen efficiency. Didjer think this would be easy? Doing it in the lab under clean test is one thing. Out in the field with poor maintenance, salt eating grounds, extreme temps, no warmups, etc. is another.
        • 5 Years Ago
        So... Did you take the greater thermal efficiency at higher compression ratio into account before writing that post? Because experts agree that the generally lower energy content of alcohol compared to gasoline is offset by the better thermal efficiency of using alcohol at a higher compression ratio!
      • 5 Years Ago
      Would it work on diesel? I wonder how high the compression is in this engine if it can run on just about anything.
      • 5 Years Ago
      So, how exactly does the top part of the engine move up and down without breaking a seal or something?

      Do they just use a rubber gasket, or some sort of magically expanding gasket? Either way, this all sounds great and all...but more parts usually just means more things that break, and expensive repair costs.

      However, it IS Lotus, and they usually know what they are doing. So who knows. I'll buy into it when they've done extensive long duration testing.
      • 5 Years Ago
      Pardon my ignorance but how's that different than the flex fuel engine available in Brazil for several years now?
        • 5 Years Ago
        My recollection is that the design above is two-stroke; yours a four-stroke. See the Sailor's posts.
      • 5 Years Ago
      This has very little to do with anything seen today in a car! It isn't "just" a flexi fuel engine. It isn't just a 4-stroke without an intake valve. And no, it doesn't come with a reed valve. The reed valve becomes redundant when you mix the fuel in the chamber after exhaust has been completed.

      I'm a marine engineer and work with two-strokes on a daily basis. It might come as a surprise to many, but the largest piston engines in the world are actually two-strokes (Google the Sulzer 14RTflex96 - I worked with one of those for three months).

      I'll try to explain this for anyone interested:

      A "regular" car engine works in four strokes;

      - Intake (intake valve open and air/fuel mix is sucked in),
      - Compression (air fuel mix is compressed by piston)
      - Combustion (air/fuel mix burns causing it to expand)
      - Exhaust (burnt fuel and air is ventilated using the piston and open exhaust valve).

      This corresponds to two full rotations of the engine for each time one piston produce power (during combustion).

      A two stroke engine combines intake, exhaust and compression into one single stroke. In a regular 2-stroke engine, this means that you are bound to get some fuel into the exhaust or have a very bad atmosphere in the combustion chamber as the exhaust gas is only partially vented.

      I'll break the process into a few more steps than two strokes:

      - Intake, the piston moves down, exposing the intake port.
      - The exhaust valve opens exposing the exhaust port. The engine will have forced induction (turbo- or supercharged) and therefore, the intake air pressure is greater than the outside pressure, since the intake port is still exposed, the clean air will force exhaust gas out through the exhaust port venting the combustion chamber.
      - The exhaust valve closes. The combustion chamber is now filled with clean air (and nothing else)
      - The fuel injector injects fuel into the chamber as the piston compresses the air/fuel mixture)
      - The compression ratio is adjusted so that you will reach critical pressure at the pistons top dead center. The air/fuel mixture ignites (due to the heat developed because of the rising pressure in the chamber).
      - The mixture combusts thus forcing the piston down and power is produced.

      What all this means, is that the engine produce power during each cycle, not only every other cycle.

      As to efficiency, well according to Lotus, the engine will have a specific fuel consumption of between 225 and 275 g/kWh(presumeably on gasoline) depending on mean pressure (ideally, the pressure should be 1 bar as this would mean that no energy is wasted), this translates into a theoretical fuel efficiency of between 40 and 50% which is basically the same as the largest ships engines. This is theoretically possible as modern two stroke diesel engines in ships have similar efficiency, however, I think it is highly unlikely that we will see that in real life - but the engine will be much more efficient than regular gasoline engines for sure!

      Sorry for the long post, but I hope it will help a few people to understand this concept!
      • 5 Years Ago
      variable compression.... impressive.

      but how do you get air in and out of it?

      I understand the wobbly bit for the exhaust
      valve.... I just never imagined a motor that
      would pump air in such a wild way.

      NO intake valves? it just gets locked off
      as the piston rises.... then after the boom
      the downstroke and that wobbly bit opens
      for the exhaust.... I just thought that there MUST
      be a valve on the intake side... but maybe not.

      looks soo complicated but if we're headed toward
      efficiency running all sorts of fuel.... I guess you have
      to achieve variable compression and I think this is
      the only way to do it.... WOW.
        • 5 Years Ago
        oh my ....

        it's a 2 stroker, you don't need regular intake valves, but rather carbon fibre reed panels

        the intake is directly on the crank case, when the piston goes down, the reed valve closes due to over pressure.
        when the piston rises, the reed valves open and draws in air.

        very old 2 strokers, prior to the 90ties, didn't had reed valves, only exclusive modern models.
        in the case the piston had an extra function, namely being also the intel valve.
        but this was bad, because fuel could drop right into the exhaust, unles you had a superduper expention exhaust.

        you could say, the reed valve somewhat quadruppled the power output.

        in the past there was a truck brand called FTF, they had 2 stroke turbo diesel, they needed intake valves, to maintain the presure.
      • 5 Years Ago
      These types of two strokes with "isolated" crank case oil *must* use a scavenge roots-type blower in order to function. Think of the old detroit-diesel two strokes.

      The variable exhaust port and two-stroke direction engine is nothing new however. The Rotax E-TEC two strokes engines have that as well. Newer Johnson and Evinrude two stroke boat motors (owned by BRP, who also owns Rotax) may also use the same technology.

      The variable compression thing seems new however.
        • 5 Years Ago
        yep, you're right, when i toke a second look, i figured, this only works with boost.

        older rotax engines found on jetskies, use a disk with a wurm screw drive.
        i had a very old (can't remember the brand, prior 90ties) trail bike, it has a disk right on the crank and very funnily curved inlet manifold.
      • 5 Years Ago
      So, what will its miles per steak be?
        • 5 Years Ago
        There is no reason for this comment to have any fewer than three stars.
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