When you thought the modern car was dead...

[retirementguy1]

Nissan revolution: could new petrol engine make diesel obsolete? | Reuters

[pb4uski]

Interesting. We bought a new Subaru Outback last December with a 4-cyl and I have been pleasantly surprised to get almost 30 mpg in mixed driving in the first 12k miles... a bit higher than the EPA fuel economy of 28 mpg.

If this new technology would increase mpg 27% that would be 38 mpg... who needs batteries!

[jazz4cash]

It is interesting but the real value for diesel technology is medium and heavy trucks, but they only discuss cars in the article. They use variable compression technology but typically you would need higher octane gas for higher compression so I wonder how they handle that.

[Big_Hitter]

is this the variable compression engine?

[samclem]

Quote:

Originally Posted by jazz4cash It is interesting but the real value for diesel technology is medium and heavy trucks, but they only discuss cars in the article. They use variable compression technology but typically you would need higher octane gas for higher compression so I wonder how they handle that.

I'm guessing they are using some sort of knock sensor to know if there is a problem with predetonation, as we already do on modern cars. But, instead of retarding the timing of the ignition to address this, they are reducing the compression ratio. In that way they can get the highest CR possible with whatever fuel (octane) and conditions (engine load, combustion chamber temps, etc) exist. If te engine isn't under load and if there are no local hot spots to cause pre-detonation, then higher-than-standard CRs can be achieved in normal driving even with the present fuels. Or at least that's my understanding. IOW, we have lower CRs today because we have to account for the "worst case", this technology allows a smarter tailoring of the CR under various conditions.

[braumeister]

Quote:

Originally Posted by pb4uski I have been pleasantly surprised to get almost 30 mpg in mixed driving in the first 12k miles... a bit higher than the EPA fuel economy of 28 mpg.

Largely related to your driving style IMHO.
I have never in my life gotten average MPG as low as the EPA estimates. Typically about 2 MPG higher.

[ejman]

I've been amazed at the mileage I've been getting with my new Chrysler 300. The EPA says 19/31 with a combined 23 mpg. I've been getting about 25/34 with a combined average (over 2500 miles so far of 30.5 mpg). For a 4,000+ lb car with a powerful V6 that is remarkable (as is the acceleration - have to remember to be gentle with that pedal). In fact the average mileage is better than what I was getting with a 4 cyl 2009 Dodge Caliber and almost as good as the mileage my wife was getting on her Toyota Corolla.

[Koolau]

I'm certain there are still some "tricks" that can be used to get better fuel mileage using ICE cars. The ever increasing sophistication and cost to increase mileage may reach a break-even point - especially if fuel costs remain low. Trust gummint to mandate the fuel mileage without considering whether it makes economic sense to do so. I have no doubt that car co.s can reach the new required CAFE limits. Whether it will save us any money is quite another question. Imagine an aluminum and carbon fiber Chevy sedan with hybrid technology (primarily for the braking regeneration capability). It will get 50+ mpg but cost as much as a current BMW or MB. If fuel remains below $5/gal, it will not likely pay for itself in the car's lifetime. And it will still be just a Chevy.

I love the technology and I'm not a Luddite. In fact, I wish I could have participated in a c@reer that contributed to fuel efficiency (and clean technology). Still, at some point, wringing a few more MPG out of a gallon of gas is going to be very expensive. It's sort of like the current "pollution" standards which tighten every few years, even though there is very little pollution remaining to be reduced. Calculations of cost/benefit seem to go out the window when the gummint decides such things. I have no desire to return to the 60s, but at some point, we may have to say "enough is enough." Naturally, YMMV.

[retirementguy1]

Being in my 30's I still think the ICE will finish its usefulness while I'm still alive but I think this is probably the biggest step forward since fuel injection.

[aja8888]

We seem to work on fuel combustion efficiency but it's that darn friction that keeps getting in the way of increasing MPG in an auto.

[Bamaman]

I just question the quality of engineering on such an engine for a company that has such a poor quality CVT transmission in most of their cars. Nissan CVT has a terrible reputation with service technicians.

[meierlde]

Actually you see start stop engines become more common with a 48v based starter/generator and battery. (Actually then if done right you get regenerative braking).

[jazz4cash]

Quote:

Originally Posted by samclem I'm guessing they are using some sort of knock sensor to know if there is a problem with predetonation, as we already do on modern cars. But, instead of retarding the timing of the ignition to address this, they are reducing the compression ratio. In that way they can get the highest CR possible with whatever fuel (octane) and conditions (engine load, combustion chamber temps, etc) exist. If te engine isn't under load and if there are no local hot spots to cause pre-detonation, then higher-than-standard CRs can be achieved in normal driving even with the present fuels. Or at least that's my understanding. IOW, we have lower CRs today because we have to account for the "worst case", this technology allows a smarter tailoring of the CR under various conditions.

It still seems superfluous to me. The CR will be limited by whatever fuel happens to be in the tank. I guess you could use premium only when you're heavily loaded or driving in the mountains. Some vehicles now recommend (vs require) premium as they retard timing or use variable valves to inhibit detonation but that is a performance trade off.


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[ERD50]

Quote:

Originally Posted by jazz4cash It still seems superfluous to me. The CR will be limited by whatever fuel happens to be in the tank. I guess you could use premium only when you're heavily loaded or driving in the mountains. Some vehicles now recommend (vs require) premium as they retard timing or use variable valves to inhibit detonation but that is a performance trade off. ...

No, that's not what they are doing. It is explained better in this video, but they lower the CR when accelerating and under load, and then raise it for increased efficiency when you aren't under such a heavy load.

In a standard ICE, the CR needs to be low enough to handle load w/o knocking. But then you can't take advantage of the higher compression ratio for more efficiency during times when you are not limited by knock.

I'm guessing that they control this by monitoring the load on the engine, and the knock sensor is an additional over ride. If they only used knock as an indicator, they'd need to continuously bump against that limit, then back off a bit to find the 'sweet spot'. That much knocking would probably cause problems over time.

https://www.youtube.com/watch?v=kV2ApRM_Pi8

Quote:

Originally Posted by aja8888 We seem to work on fuel combustion efficiency but it's that darn friction that keeps getting in the way of increasing MPG in an auto.

Friction isn't the biggest issue, it's that darn Carnot limit. An ICE loses most of it's energy (~ 60%) to heat through the cooling system and exhaust. Friction is just 3%, and ~ 10% more for the drive-train and tires. Add in wind resistance depending on average speed.

https://www.fueleconomy.gov/feg/atv.shtml

-ERD50

[meierlde]

Quote:

Originally Posted by ERD50 No, that's not what they are doing. It is explained better in this video, but they lower the CR when accelerating and under load, and then raise it for increased efficiency when you aren't under such a heavy load. In a standard ICE, the CR needs to be low enough to handle load w/o knocking. But then you can't take advantage of the higher compression ratio for more efficiency during times when you are not limited by knock. I'm guessing that they control this by monitoring the load on the engine, and the knock sensor is an additional over ride. If they only used knock as an indicator, they'd need to continuously bump against that limit, then back off a bit to find the 'sweet spot'. That much knocking would probably cause problems over time. https://www.youtube.com/watch?v=kV2ApRM_Pi8 Friction isn't the biggest issue, it's that darn Carnot limit. An ICE loses most of it's energy (~ 60%) to heat through the cooling system and exhaust. Friction is just 3%, and ~ 10% more for the drive-train and tires. Add in wind resistance depending on average speed. https://www.fueleconomy.gov/feg/atv.shtml -ERD50

Actually the Carnot cycle is why diesel engines start out ahead of gasoline engines because the combustion gases are hotter.