Infiniti's variable compression ratio engine "Could Kill Diesel Forever"
Although people in the comments say Saab actually came out with a variable compression engine first.
The World's-First Variable Compression Ratio Engine Could Kill Diesel Forever Quote:
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Funny I just read about this earlier. Just when you think the internal combustion engine has peaked, this comes along. Clever stuff indeed, no doubt we'll see it in future Renault models too as they are the same company now. I'd be super sceptical about economy figures though, this clever engine tech can often promise so much and deliver very little, but time will tell. I can't imagine it would come close to a diesel for fuel economy.
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Wonder how much extra this variable-compression trick will cost ;)
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They say it costs less than a diesel engine, but it obviously cost more to develop and test it. There may be an initial higher cost to cover recalls, insurances, warranty and maybe the odd premature failures. New tech always costs more, but drops significantly in time.
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I'm sure there will be no confusion whatsoever in conversations with VCT and CVT in the mix. :)
I wonder what fuel it will require and how the same fuel will perform equally well at 8:1 and 14:1 compression. |
As long as it has a good knock sensor strategy, it should be fine. But my guess is it will require high-octane just for the safety net.
My Mustang has an adaptive tune that will run normally on regular unleaded, but actively advances cam- and spark-timing as far as it can, so performance increases as octane goes up. |
Maybe you can half fill the tank with petrol and half diesel, then it has a fuel for each compression! I'm kidding by the way...
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I'm waiting until this is in production and real number and experiences have logged plenty of miles before I get excited.
A gasoline (petrol) engine works on an entirely different principle than diesel. A big difference is that a gasoline engine introduces a calculated fuel-air mix into a cylinder, compresses it (at a fixed or now variable compression ratio), and thenvignites the fuel/air mix using a spark plug. It must always be sure to avoid pre-ignition, or detonation, or risk damaging the engine. A diesel compresses only air at a very high ratio, and to such a temperature that when the injector introduces fuel, it instantly ignites in the hot cylinder (assuming the engine has warmed up and the glow plugs are off). With today's computers, the precise injection of diesel fuel can be varied not only in volume, but in time relative to Top Dead Center (TDC), as well as with multiple pulses at various times throughout the detonation cycle. This gives diesel engines a lot of flexibility in this area, which gasoline engines simply don't have. The other factor is the price of the fuel. Where I live, diesel has been cheaper than regular gas, ever since I got my car. Will the variable-compression engine run on regular, or likely need the much more costly premium gas, which has a higher octane rating to prevent detonation at higher loads and higher compression ratios? MPG is not the only factor. "Cost Per Mile," the more useful metric, takes the fuel price into consideration as well as he fuel economy. As I said, I'm not pooh-poohing this new engine. I'm just regarding it with some cautious skepticism before I conclude that it's the new savior. |
I think Saab's system actually lifted and lowered the head block to vary the compression.
If the engine is direct injected, regular octane will be fine, but it could work with port injection. With VVT, the fuel charge will never see the 14:1 compression pressures for the efficiency mode; it is using an Atkinson cycle. The Prius has a 13:1 ratio with port injection. The intake valves close late during the compression stroke. The fuel charge is seeing a 10:1 CR at most. The higher compression ratio allows for a longer power stroke to extract more energy from the burning fuel. That 14:1 compression ratio should really be called an expansion ration. The question I have is what this system adds that a full range, Otto to Atkinson, VVT doesn't. Such valve timing systems are starting to come to market too. |
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