This appears to be a theoretical study without any prototype being built as yet--at least that's what appears from skimming the paper. Looks like a creative and very practical approach to improving fuel economy significantly with off-the-shelf technology. I hope to see more about this.

Thanks, I stand corrected. I misunderstood into thinking the engine was to be run on ethanol only, and not as an additive.

Mark,
"Does anyone automaker currently offer direct injection, of gasoline, in any vehicle currently for sale?"
Yes there are few of them: GM,VW, Mercedes. As a matter of fact my '91 Cadillac Seville had direct injection (I know because I had to replace those injectors few times)

GM is not using direct injection in any gasoline engines...yet. The Solstice GXP will be their first application this fall though. Audi/VW have done a great job with it in their 2.0 Turbo that is used in the A3, A4, Jetta, and Passat. Lexus uses it on 3 naturally aspirated engines so far - a 2.5 and a 3.5 in the IS and a 3.0 in the GS. Mercedes is also using it, and BMW will be in the fall as well.

However, to the best of my knowledge, none of them are using the most advanced super high pressure "micro piezo" versions yet (I believe Mercedes will in their upcoming BluTec Diesel). That is where the big gains in fuel efficiency will come from, because of the ability to run a very lean air-fuel mixture.

Mazda is also using direct injection on their Mazdaspeed 3s, or whatever it's called. Honda uses direct injection on a version of the Stream minivan, although it has never been sold in the USA. DI is just about the last big thing for gasoline engines as far as increasing volumetric efficiency. After DI is commonplace, nearly all further gains will have to come from downsizing, forced induction, and hybridization.

Direct injection has nothing to do with volumetric efficiency.

Volumetric efficiency is a measure of how much air your engine pumped relative to it's displacement.
Air is the limiting reagent in the chemical reaction, more air lets you use more fuel = more power.
A higher volumetric efficiency lets you get more work out of an engine with smaller displacement.

variable valve timing/lift etc is a big thing for engines as far as increasing volumetric efficiency.

There are many times where you want to operate at less than 100% power ... so you throttle the engine with the carb/ throttle body but this increases pumping losses.

The BMW valve-tronic adjusts valve timing and lift and eliminates the throttle plate.

Because most vehicles have a fixed number of discrete gear ratios the engine has to operate over a range of speeds.

This is bad for efficency, the intake / exhaust manifolds cam shaft(s) that work great at 6000 rpm suck at idle.

This is why you see variable length intake manifolds and variable valve timing systems to try make the engine run well over a wide rpm range.

GM uses an exhaust cam that can be advanced or retarded, honda uses 2 camshafts one for high rpm and one for low rpm operation.

Chrysler, GM, and others use cylinder deactivation to reduce fuel consumption under low load.

DI + variable valve timing does allow you to do some cool things like stratified charge combustion.
Reading on this subject is left as an exersize to the reader.

How sad that no one (in the USA) ever realizes that Mitsubishi was the first company to mass market a Gasoline Direct Injection powered vehicle. They had a 1.8L 4 cylinder GDI engine back in 97 being used in the Japan market Lancer. Now it is a 2.0L GDI and turbo 2.0L GDI engine in the Lancer. They use a 40:1 air fuel ratio thanks to GDI.

Many drag racers have used ethanol injection when they turbocharged naturally aspirated motors and did not want to put in lower compression pistons. Hyundai McIntyre in El Paso, TX (well it is owned by someone else now but back in the late 90s it was owned by McIntyre) used to spit out turbocharged vehicles with Ethanol injection to support the additional power. They would have 140hp 2.0L motors pushing 300hp with no intercooler on stock compression, stock internals (with a t3/4 hybrid garrett turbo) simply through the use of ethanol to cool the incoming air and provide fuel to support the extra power.

ADI (Anti-Detonation Injection) was used on the large piston aircraft engines from WW2 up to the 1950's. This looks like a sophisticated version of it, could work very well. I'm supprised we haven't seen something like this sooner.

Everybody: welcome to performance DIY world. Some information for starters:
1) dual fuel injection is well-established practice to boost performance of existing engines. Usually it is intake manifold injection of methanol/water mix to improve volumetric efficiency, increase octane number, and provide full throttle rich-out. Ethanol, as inferior of methanol, is not usually used ( methanol, as being formerly produced from wood and bearing name of wood alcohol, currently is much more economically produced from NG; hence, not sexy enough for environmentalists). Sometimes this technique is used on stroked engines to allow use of regular gasoline with high-octane methanol/water injection on full throttle. On diesel engine close controlled methanol/water injection boost max torque/power by 30%.
2) Among scientific/engineer/journalist community it is common practice to claim that direct injection Ggasoline engine can boost fuel economy by 30%. It is a lie. The truth is that stratified charge direct injection gasoline working at substantially less then stoichiometric air/fuel ratio could achieve fuel efficiency gain up to 30%. This is exactly the case with outboard marine engines, because of much relaxed exhaust emission regulation. Unfortunately, for cars it is not the case. Three way catalytic converter could work only if exhaust is close to stoichiometric ratio. That means that gasoline direct injection engines, such as bravely sold by VW/Audi, could maintain only (or whopping?) 10% fuel efficiency gain.
3) Billions of dollars are invested recently to develop NOx adsorber cat converters, capable to work on lean air/fuel ratio. My bet that first commercial applications will be on the road in about a year. From that time on, expect 30% fuel efficiency gain for GDI engines and oblivion of diesel power for passenger vehicles.

Requiring consumers to maintain not one but two tanks of rapidly consumed liquids at sufficiently high levels represents a substantial barrier to market adoption. Witness the (otherwise unrelated) requirement for AdBlue in diesel engines with SCR systems. Setting up a production and continent-wide distribution infrastructure for a new fuel is also a daunting task.

Note also that in the proposed architecture, the high octane number of alcohols (ethanol, methanol) can only be exploited at very high boost ratios, since the geometric compression of the engine is limited by the gasoline that is normally burnt. Turbochargers that deliver high boost pressures are relatively large (= high lag) and only become effective near nominal load. However, all system components, from air filter to intercooler to crankcase, piston, crankshaft, valvetrain, manifolds, catalyst etc. also need to be adapted to this worst case mechanical and thermal load. This combination of downsides renders the proposal rather marginal IMHO.

The more sensible approach to radical downsizing gasoline engines is to combine the turbocharger with a mechanical compressor that is only used at low RPM (VW Golf GT) or, via hybridization. The latter is accomplished e.g. via electric assist to the turbocharger (Garett, Caterpillar diesels) and/or an integrated starter-generator (FEV study for Audi). In NA engines, a small turbogenerator may be fitted in a bypass of the exhaust manifold to power various pumps and the a/c without recourse to shaft power.

Throttling losses can be reduced using variable lift valvetrains on the intake side (BMW, Porsche, Honda, Toyota, ...). A related / competing concept for large engines is displacement-on-demand a.k.a. cylinder deactivation (Honda, GM).

As for GDI, only the second-generation spray-guided systems have significant impact on fuel economy. This is partly because they raise the knock limit via evaporative cooling but mostly because they permit stable ignition of a highly stratified mix with global lambda >> 2 in part load. In homogenous mode, lambda ~1.6 is the limit for gasoline ignition. With CNG, especially if it is blended with a small fraction of hydrogen, the ignition limit for a homogenous mixture is lambda > 2.

However, all of these lean-burn concepts require fairly expensive NOx aftertreatment (cp. diesel) to meet emission regs, or else HCCI (still stuck in the lab).

You don't really have to have two tanks. By ignoring port injection altogether, you could quite easily end up with a GDI FFV which would run from normal petrol to alcohol eg E85.

The conceptual advantages of direct injection alcohol are still valid. Having a duplicated injection system with different fuels is highly unlikely to work in-market and froma cost POV having duplicated injection hardware is also pretty uneccessarily profligate!

Yes I know they are but not with differing fuels for each system.

Dual systems are still a very expensive for the benefits they actually create when pure DI can be done easily. See Euro VW range... If you do DI properly, you don't need PFI....