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Turbomachinery typically doesn't scale down very well - Reynolds number effects (has to do with turbulent flow and fluid-dynamic losses) become killer when the size goes down. Also, the Brayton cycle (gas turbines) either requires a very high pressure ratio (only achievable with multi-stage compression and expansion) or very efficient regeneration and recuperation (only achievable with heat exchangers having large surface area and low flow losses i.e. they have to be BIG) and I see no evidence of that. The website mentioned above makes no mention of thermal efficiency or BSFC or anything of the sort ... and all this makes me think it's likely pretty poor.
Spark-ignition premixed-combustion engines on standard pump gasoline become knock limited very easily. Add more boost, and you have to drop compression ratio down or delay ignition timing or add lots of enrichment. It's not necessary to stack boosting devices in series to reach these limits! Thermal loading on pistons and exhaust valves (and catalytic converters) is a big issue. Direct-injection can help with knock control but they all run premixed-combustion under load which limits how far this can be taken. Diesel-style injection late in the compression stroke is resistant to detonation but not good for emissions. (same PM and NOx issues as diesel has) Yes, higher octane fuel (including ethanol) would help with this! It addresses the knock, but not necessarily the thermal loading. You can still melt a piston or an exhaust valve without detonation, although detonation makes it happen a whole lot sooner and faster. As mentioned above, I am quite sure that Ford crunched the numbers and did the simulations, and ended up with an exhaust-driven turbocharger on the Ecoboost for good reason. Use of a turbocharger is still compatible with running cam timing that emulates the Atkinson cycle at part load, to divvy up the energy in the exhaust between the pistons (turning the crankshaft) and the exhaust turbine (turning the turbo compressor). Yes, the supercharger will give more boost right off idle ... where detonation is at its worst. Or you can just change into the right gear when you need power, instead of lugging the poor thing ...
Hmmm ... Torotrak has been kicking around for quite a few years. If this really was an "Ecoboost" engine then the "incumbent" forced-induction device is a conventional exhaust-driven turbocharger, not a mechanically-driven positive-displacement supercharger. I gather that they are proposing to use this as part of a twin-charging scheme, as a supplement to a turbocharger to help out with low-end torque. The inability to fully convert remaining exhaust pressure into crankshaft torque by overexpansion (e.g. Atkinson cycle) does not act in favor of a boosted downsized engine, particularly when it's running under heavier load (on boost). Call me skeptical; our family's real-world experience with boosted gasoline engines has been that they are not more efficient in the real world than a bigger, but less highly tuned, normally aspirated engine ... If someone can figure out a way to get them to run under load on boost without enrichment and without melting themselves down, that would help. Cue Bosch's water-injection system ...
... except that none of those technologies are ready for prime time, the cost is not "low", and none of that in any way affects the velocity-squared relationship of aero drag in any case. Hypothetically making a vehicle self-driving doesn't miraculously make aero drag go away, and changing to a different fuel type doesn't change the velocity-squared consumption of whatever fuel type you are using. Ontario, Canada has chosen 105 km/h for the truck speed limiter setting a few years ago. It's doubtful that this has had any real world effect on safety; most truck collisions don't involve driving at a steady speed on a motorway. It has probably cut fuel consumption, and it has rendered trucks almost incapable of overtaking each other, which is really annoying. The choice of 105 km/h for the truck speed limiter setting is a tacit admission that Ontario's highway speed limit of 100 km/h is too low.
General aviation aircraft engine technology is roughly on par with the old air-cooled VW Beetle. No updated valve seats (that would allow use of unleaded fuel), therefore no catalytic converters, no emission controls at all. If they have fuel injection, it is an old open-loop design. Any change has to get through FAA certification, and the FAA is pretty resistant to change. It's hard to put new aircraft and powertrains on the US market due to the stifling legal environment, so old stuff keeps getting re-used and rebuilt again and again, and it has to run on the same leaded avgas that it always has. A number of more modern powertrains have been developed for aircraft use, but they have not made it to the end users in appreciable numbers.
The remaining challenge will be achieving this affordably. That's going to take longer. 500 km electric range in a car that costs $150,000 does me, and every other average non-rich person, precisely no good whatsoever.
That's the Atkinson (or Miller, if you wish) cycle. Nothing in Nissan's variable-compression-ratio system precludes the use of cam timing trickery to achieve Atkinson/Miller cycle operation. The "efficiency versus power" tradeoff relates more to cylinder pressure and detonation limitations. It can only operate at a very high compression ratio at lighter load on the engine (when boost pressure is low and intake is restricted - whether by throttle or by cam timing trickery is irrelevant). It becomes detonation-limited and peak-cylinder-pressure-limited at high engine load which means the compression ratio must be lowered (and BSFC suffers). You can rest assured that Nissan already knows how to do the Atkinson/Miller cycle, and they already know that they want to use the highest compression ratio that can practically be achieved under given operating conditions.
There is zero chance that a vehicle like this would be granted an exemption from collision standards in the foreseeable future ... unless it is a motorcycle.
A harmonic-drive gearbox is a type of high-ratio gear reduction unit (100:1 gear reduction is possible in a single stage). A stepper motor would be the most likely choice to operate that, and yes, the motor would be under direct ECU control. It is also possible to do it hydraulically based on engine oil pressure through a directional valve; VVT mechanisms already do this. It seems from the diagram that Nissan has chosen a harmonic drive reducer which would almost certainly be driven by a stepper motor. Stepper motors are already in common use for actuators that require high positioning accuracy (which this does). If high positioning accuracy is required, the hydraulic method is not so easy. VVT mechanisms use hydraulics because the adjustment has to be done inside a rotating assembly (the camshaft and drive pulley/sprocket). Controlling the position of an axis (the variable-compression mechanism) via a stepper motor in response to any inputs you care to choose, is a trivial exercise for modern engine control units. Feedback via knock sensor is almost certain to be part of the control strategy. Ignition timing would remain part of the knock strategy because it can respond on the next engine cycle, whereas the compression adjustment mechanism would take longer to react. Again, this is not a problem for modern engine controls. The ignition timing control loop is the "fast" response and the compression ratio control is the "slow" response. As for air/fuel ratio ... Given how the standards have been written and how the engineers have figured out how to (mostly) comply with them, this ain't gonna change. The standards have locked us into stoichiometric air/fuel ratio with lambda sensor and 3-way catalyst. You can play with exhaust recirculation, either via an explicit EGR system or by cam timing trickery, but air/fuel ratio remains stoichiometric. The variable compression mechanism in no way changes or affects this. Even if HCCI is used, it will still be stoichiometric, just with varying amounts of EGR - so that it can use a normal 3-way catalyst. Nothing else that we know how to do, is sufficiently future-proof. (Ask VW.) I agree with the statement that you can have efficiency or power, but not both simultaneously ... unless you are using high octane fuel (like E85) ... Modern engine controls, with knock sensors and lambda sensors, can figure out what mix of fuel is in the tank (within reason) without actually measuring what the fuel is. Gasoline is such a concoction of different compounds that measuring its properties in the fuel tank isn't all that reliable. But the knock sensor and the lambda sensor are enough to tell the engine controls what they need to know. The person who puts diesel fuel into the tank of a spark ignition engine is gonna be in trouble no matter what.
Arnold, what are you talking about? Infiniti's variable-compression system works with a normal DOHC 4-valve cylinder head and doesn't care whether the engine uses port-injection with premixed combustion, direct-injection with premixed or stratified charge, or both. It's also a really good way to facilitate HCCI over a much wider range of speed and load than otherwise possible. It doesn't care what the fuel is ... if anything, this system would allow operation on high percentages of ethanol in high-compression mode, thus taking advantage of the high octane rating of ethanol in a way that today's conventional flex-fuel engines can not. (For example, under given conditions, 87 octane gasoline might limit compression to let's say 9:1, but E85 would allow the compression under the same load conditions to be let's say 12:1, thus improving efficiency under those load conditions.) Knock sensors are commonplace today. Real-time combustion pressure sensing is not common but it is in production (many current emission-controlled diesels have it). The ability to vary the compression ratio opens up options for how to deal with the detection of knock. My main concern is combustion turbulence. Modern combustion chambers require the piston to approach the head closely in squish bands around the outside of the chamber, which improves turbulence and accelerates combustion. With this compression-adjustment system, when it is operating in low-compression mode, can't do that, because the piston no longer closely approaches the head!
Yes, I will grant that I did not read your self-promotion paper carefully, and I'm not planning to. The main point is that Nissan's development fits within the shape, envelope, and general architecture of a normal in-line 4-stroke piston engine, and yours doesn't. I saw piston-porting in the first diagram in your paper that I encountered, and stopped reading right there. It's problematic for emissions and lubrication. Ask Detroit Diesel.
Did they consider the large number of urban dwellers who live in apartment buildings, condominium units, downtown properties without access to recharging? It sounds plausible that 90% of trips are within the capability of current EVs but it doesn't sound plausible that that 90% of people have access to charging. Infrastructure needs some work to make this happen. Every trailer that I've ever towed increases fuel consumption by 30% - 50% because it buggers the aerodynamics of the tow vehicle. If you're going to have a range extender it needs to be on-board to avoid this. If it's going to be on-board then the space needs to be allocated in the vehicle for it. If the space needs to be allocated in the vehicle for it then it might as well be there all the time. Car sharing means you're sharing the previous owner's detritus left in the car unless someone's being paid to clean it after every use, just like normal car rentals ... up goes the cost ... Like it or not, lots of people are pigs. Car sharing also means I can't leave my hard hat, safety vest, tool box, etc in the car. It might work for some people but it won't work for all people ...
T2, Fiat already has the TwinAir engine (another one that I really like). A parallel-twin engine isn't necessarily less expensive nor more efficient than an inline-three, though. The Ford three-cylinder, and a number of others, can get away with not having a balance shaft if the engine mounts are carefully designed, but with a parallel-twin, it's pretty much unavoidable. In motorcycle applications, the NVH can be accepted in some cases, but most people wouldn't tolerate it in a car. The Fiat TwinAir is counterbalanced. I have my doubts that cylinder de-activation on an engine this small would save much in the real world ... it may just be another thing that increases the discrepancy between the EPA / NEDC tests and the real world. I have a car with a 1.0 3-cylinder, and it doesn't spend a whole lot of time at light engine load and higher revs where cylinder de-activation could help. Real world highway driving, the load on the engine is already pretty high most of the time. Real world city driving, the revs are low and cylinder de-activation would probably give unacceptable vibration. Cylinder de-activation schemes generally don't operate at low engine revs.
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.