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Well, not exactly. GM tried it in the early 1980's (the infamous Cadillac V8-6-4) but engine controls were not advanced enough at the time to do it properly. To avoid driveability problems, there has to be a step change of throttle position, valve timing, ignition timing, fuel delivery, etc at the moment of switchover. Couldn't do that (with production-ready technology) in 1982. Now, it's no problem. The mechanics have to be designed into the cylinder head, not added on, too.
The measures listed above are not going to improve consumption by "6-8%". There's not enough weight or aero reduction there. And a plastic exhaust system?? Come on; the temperature even at the very back of the exhaust system is more than plastics will tolerate. Anyway, I am in agreement with cujet about the Prius's driving dynamics (I've driven one, and found it unacceptable for what I want from it). And what's missing from the list of improvements is the thing that most needs to be fixed ... the steering! For what it's worth, I have the same criticism of other late-model family-oriented Toyota cars that I've driven. The steering is waaaaaayyyy too over-assisted, leaving zero feedback to the driver. Message to Toyota engineers: Go drive a late model VW Golf. Or even a 3-series BMW. Make the steering like that. It costs nothing (in either money or fuel-consumption ratings) to make steering with proper road feel ... and it might get a few drivers used to European products to look at yours!
What is so special about this? Every fuel injected engine that I have ever dealt with, has deceleration fuel cut! Some are more aggressive (and more annoying) than others, but they all do it.
Automatic in the form of "automated-manual" transmissions have been around for a long time, but the innovation of using two clutches to control alternating gears to enable smooth gear changes has not, and the computing power to co-ordinate which gear to pre-select and to co-ordinate disengaging one clutch and engaging another has most certainly NOT been around "50 years ago" and to even suggest that is an absurdity. Computers back then were the size of a house and cost a fortune. Could it have been done without such computing power available? In some sort of fashion ... sure. But without the benefit of a torque converter to smooth out gear changes and without very careful control of the mechanical clutches, and without control of engine load while changing gears (requires drive-by-wire), it would have been a very jerky experience that almost no ordinary people would have considered acceptable. Actually, there is an example of such a transmission available right now, in the Smart car. Go drive one and come back and tell us what most people think of the transmission in those. (That one has an automated-manual but without dual clutches - and it even has drive-by-wire, but it's still a disaster in terms of smoothness and driveability.) In the 1960's, power and smoothness were priorities over economy. Like it or not, that's the way it was. Folks who weren't or aren't willing to accept the inefficiency of a traditional automatic transmission have always had the availability of a good old-fashioned row-it-yourself manual transmission ... and that's what I do.
Granted, if you use a variable valve timing and lift mechanism with considerable authority over the intake valve closing event. BMW Valvetronic and Fiat Multiair are like this. Neither one seems to get wonderfully spectacular fuel consumption figures. The compression ratio on a normal (premixed) gasoline engine is limited by detonation concerns at full load. If you deliberately sacrifice torque rating of the engine by deliberately ingesting less than a full charge, then yes, the expansion ratio can be bigger than the effective compression ratio (Toyota Prius does this) - it results in low specific torque output. Mazda Sky-G has a 14:1 compression ratio and a rather diesel-like combustion chamber, and I suspect that they are injecting the fuel late, almost in diesel-like manner, but with spark ignition. Remains to be seen whether this engine will really live up to its promise; we should find out soon enough. The Fiat 500 Multiair has disappointing EPA ratings. The 1.3 Multijet diesel is still the engine of choice in that car ...
This is a piston-ported engine. How are they getting around the lubrication of the cylinder walls leading to oil either getting into the combustion chamber or going out the exhaust? Detroit Diesel never figured that one out (and they had 50 years of production to do so), and they only had this situation on the intake ports (where most of said oil would at least be going through a combustion cycle).
... and much lower pumping losses, due to unthrottled operation.
Rytooling, all modern supercharger designs have a bypass valve that disengages them when the engine is running at part load. When the bypass is open, the supercharger is spinning, but not consuming significant shaft power. The bypass only closes when the driver requests close to full load. I will agree that a turbo is more efficient in most cases, but if you are using the Miller / Atkinson cycle (which this engine does), there may not be enough pressure remaining at the end of the exhaust stroke for a turbo to operate decently.
And what's the prime mover for that hydraulic hybrid ... A combustion engine. Better off with that engine as efficient as possible. Sheesh ...
Two-cylinder engines have considerably worse vibration characteristics and aren't necessarily any more efficient in this size range. The whole idea with supercharging and downsizing is that the supercharger is NOT required for most things that the driver does (because it's an efficiency-killer when it is in use) but is there to give extra power when the driver needs it. If you downsize too far, and the engine ends up having to run under boost a significant amount of the time in order for the car to get out of its own way ... that's counterproductive.
HarveyD, your son would not have bought one of these cars. They're not even on the market yet. Your son might have bought a *similar* car, but it won't have been this one. If it was in the 2001 - 2002 model year timeframe, it's not the same car. If it was a North American specification model (I don't know where you live), it would have had a conventional torque-converter automatic transmission, which was not particularly efficient. The DSG is a whole different ball game. This new one appears to be mechanically the same as the current (2009+) Jetta/Golf TDI. I have a 2006 model (previous engine) and it will routinely go 900+ km until low fuel lamp, even in the winter (yesterday's fill-up was at 956 km and the lamp was not on yet). My dad has a 2011 Golf TDI which is the same engine/trans as the upcoming Passat, and his fuel consumption is very close to the same as mine. If there's a Golf TDI that is only going 800 km per tank, there's either something wrong with the car, or there's something wrong with the driver.
What's the brake specific fuel consumption? This has traditionally been the weak point of automotive/truck turbine engines. Turbine engines work well at a utility power generation scale, where you can use multiple stages of regeneration and reheat and recuperation, etc., but they don't scale down well. They don't like starting and stopping, and they don't like running at part load (efficiency drops like a rock). Great for a central power plant. Not so great for a motor vehicle. If the BSFC is not equal or better than a diesel engine (exhaust aftertreatment or otherwise) or a high-compression spark-ignition engine tailored to run on natural gas, this is a non-starter.
Regarding the peak efficiency numbers: The standard efficiency calculations take no account of the Atkinson cycle. The expansion ratio is assumed to be the same as the compression ratio for both the ideal Diesel and Otto cycles. Using the Atkinson cycle extracts some useful work over and above that. Granted, we don't know if the research engine was using that, but it's not difficult to imagine that it did. The research engine overcomes detonation of gasoline by injecting it late enough in the compression stroke that the fuel does not reach detonation conditions. It does self-ignite (that's the whole idea) but the idea is that the fuel is not evenly distributed in the cylinder, so it burns progressively rather than detonating. It is mechanically a combination of a gasoline engine and a diesel engine. Many production direct-injection gasoline engines are also doing this to fight detonation, although not even close to the same extent that this research engine does. One would imagine that the combustion process is very fast - closer to the ideal Otto cycle (constant-volume). For a given compression ratio, the idealized Otto cycle has a higher efficiency than the idealized diesel cycle. I get 69% for an idealized Otto cycle at 18:1 compression and that doesn't account for the possibility of some Atkinson operation.
You save more fuel by putting a 3.5 Ecoboost into, say, a Ford F150 (replacing a 4.6 or 5.4 V8) than you do by putting a 2.0 Ecoboost into a Focus (which already has a 2.0 litre engine, just without the Ecoboost trickery). To the "ban all the trucks" contingent, who seem to be in ample supply in the above several posts, Ford still needs to sell vehicles that people will actually buy and that they will actually make money on. Smaller versions of the Ecoboost are coming, in smaller vehicles. But will Americans buy them ... ? ? ? And the contractor bringing stuff to a construction site is going to be arriving in a truck or van, for the foreseeable future.