retirementguy1
Recycles dryer sheets
- Joined
- Apr 21, 2014
- Messages
- 233
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 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 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.
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. ...
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.
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.
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