Why no direct injection?

I had previously thought that direct injection only helps standard Otto cycle engines to obtain a longer expansion stroke, to maximized efficiency, as spray of fuel cools and allows a higher compression ratio. I thought the point is moot for an Atkinson cycle.

The new Lexus GS450H uses Atkinson cycle AND direct injection. So it seems there is something to be gained there. The question is, why not the Prius? Cost to benefit ratio? I can't imagine a higher pressure fuel pump and moving the injectors will cost all that much more...

Direct injection is much more complex in execution that it is in basic concept. I think it will eventually filter down to the Prius even though it's advantages aren't as big with a psuedo Atkinson cycle engine as with an Otto cycle engine.

The Prius could benefit greatly by downsizing to a 3 cylinder engine like FoMoCo has done with its 1.0L 3 cyl turbocharged DI EcoBoost engine or with the new Nissan 1.2L 3 cyl supercharged DI engine.

I would expect the Prius might reach 60 mpg average if Toyota decided to plant an engine like this under the bonnet. But at what cost! I don't know how much more these engines would cost compared to the vanilla 4 cyl engines the Prius family uses today.

The average Prius driver does not want higher output of the 4 cyl. currently offered. It would be nice, sure, but I would rather have 60 mpg instead of 200 hp in my next Prius. And if Toyota offered the higher output 4 cyl it would be at least a $700 upcharge compared to the ho hum standard engine.

I want a 200hp 60 mpg car.

And I'd rather pay more for that than all the gizmos Toyota packages in the higher trims on the Prius. I don't really need a solar roof for instance.

Does the 1.0L Ford engine have a better BSFC that the Prius engine at typical Prius power levels? I doubt it but would like to see the numbers.

The Orbital, air-assisted, direct injection system is the one I think has the most application. The fuel is injected along with a stream of high-pressure air during the compression stroke. This high-pressure air stream atomizes and pre-mixes the fuel to minimize soot formation when spark ignition lights off the charge. Best of all, pressures are moderate compared to diesel and it supports a wide range of fuels.

The problem with diesel injection is the fuel enters as small droplets and combustion occurs from the surface towards the center of the droplets. This rich burn area leads to soot. In contrast the high-velocity air stream in the Orbital injector tears the droplets into much smaller pieces, a turbulent mix, and vaporizes most of the fuel into combustible gasses. The extra mass from the injection air also promotes better mixing throughout the cylinder air charge.

Bob Wilson

I would think the Prius would benefit mpg wise by having higher electric torque and allowing that torque at higher rpm's than it is allowed now. Something like a Prius HO with a posi that has 300 foot pounds of torque from zero mph to the limiter. That car would fly yet could get high mpg numbers because of the increased use of the electric motor. It would require a higher capacity battery bank to supply the increased current to the electric motor. Imagine a 13 something second quarter mile time in a Prius yet still gets 50+ mpg when driven normal That car would sell. Make that an option for those that like a quick car yet being a Prius and saving gas.

But back on that direct injection, the Hyundai Elantra uses direct injection on it's 1.8 liter and I proved that car can be driven thousands of miles getting 46-49 mpg highway and 32-33 mpg city. Add in start/stop technology and the city mpg will go way up. Direct injection works in their motor. I don't see any reason why it wouldn't work on the Prius. Also the Prius software needs to be reworked so it can run anything from E100 to E0 fuel, so a owner can run the higher E fuels to use even less foreign oil. As is the 3rd Gen Prius runs fine on E0 to E57 gas.

Mike

Didn't find Ford 1.0L BSFC, but I did find VW 1.4 TSI (125 kW) on page 20-23 in this document:
http://www.prof-ges.com/lectures/HTL_kfz_2010.pdf

This would suggest that TSI engine has peak efficiency of 34%. I think the main advantage of Prius engine is high efficiency from low power (>10kW), where this TSI example reaches high efficiency at 40 kW. Yes TSI from example is higher output engine, but even lower powered TSI engine wouldn't reach high efficiency at 10 kW but more like 25 kW if of course you are in the right gear.

Did find something from Ford:
http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2011/adv_combustion/ace065_rinkevich_2011_o.pdf
But from the graphs BSFC never gets over 255 g/kWh

I think Mazda is doing a better job with their Skyactive gasoline engine with high compression ratio, but did not find any BSFC map, only this:
Green Car Congress: Mazdas new SKYACTIV gasoline and diesel engines are steps on the road to its Ideal Engine; focus on compression ratio

Hi Mike,

I was listening to "Autoline This Week" where the reviewers were claiming the Nissan Altima was a 'best in class mileage.' Sad to say, www.fueleconomy.gov data, 32 highway and 23 city, didn't seem to support that claim. Then I saw your note and thought to take a quick survey:

metric	2012 Elantra	2012 Passat TDI	Camry hybrid	Prius
passenger volume	96 ft{3}	102 ft{3}	103 ft{3}	94 ft{3}
combined MPG	33 MPG	34 MPG	41 MPG	50 MPG

Fuel Economy

The order of this table reflects an insight Chris Hogan shared many years ago, multiply the payload volume, in this case just passenger, times the MPG to give a '(ft{3} mile) / gallon'. FYI, the Elantra mileage shows up 40 highway, and 29 city, similar ratios to your best metrics, 46-49 highway and 32-33 city. I tend to follow EPA values since they are somewhat reproducible across all vehicles. My takeaway:

• Both Camry hybrid and Passat TDI have better mileage and more payload
• Prius has equal payload and significantly better mileage

Direct fuel injection has a future part to play but by itself it is no magic bullet.

Bob Wilson

ps. Projected Elantra numbers in 2013, (.45*38)+(.55*27) = 32 MPG combined, vs. 2012 (.45*40)+(.55*29) = 33 MPG. Hopefully the 2013 Elantra numbers will be better than projected.

The new 2013 Altima 4 cyl will be rated 27 city and 38 hwy.

Ford has a ways to go to get the same or better BSFC as a Prius (230 g/hp-hr or better over wide operating range). I believe Mazda's Skyactiv is a pseudo-Atkinson cycle so might be better than the Ford

The prius is based off an engine that doesn't have DI. Until Toyota adds it to the engine, its expensive. Once they do, DI is is great cost benefit. Toyota did say they were having trouble combining DI and atkinson. Late intake closing means there is less time to use the injection to cool the cylinders, but this does not seem like a major problem.

I have not seen a bsfc of the ford. This engine should warm up faster do to both its smaller size and cast iron block, reducing warm up penalty. It also should have lower bsfc at lower power levels. How it does above, say 13kw where the gen III ice does very well requires seeing the chart, simply thinking about the tech won't do it. We do know it is a more expensive engine to manufacture, and a prius application would likely have a different turbocharger to maximize efficiency at the power levels the prius uses most.

This is where turbo choice comes in, a 1L ecoboost definitely should be of higher efficiency at low power levels. That engine you are looking at has a supercharger that adds a load at lower rpm levels. The ecoboost is turbo not turbo+supercharging.

I have not seen bsfc published from skyactiv either. The big difference between this and ecoboost is cost, the skyactiv should have lower peak efficiency but cost less too. Think of it this way, from a marketing point of view its a tough sell to spend more for a car that gets 1 or 2 mpg more, but has a three cylinder, and costs more. Skyactiv really adds multi-mode valving, a complex header, better cylinder design, and di to something like a prius engine. A regular gas version has 13:1 compression the same as the prius. Which means that skyactiv can run at the same atkinson type valving and otto valving, allowing the engine to be down sized for the same power, or down speeded for lower friction at higher power. I would expect toyota to do some of this in the next gen prius.

I think thats the way to go for the next Prius. Turbocharging an engine that is suppoused to start / stop immediately when not needed is not the best way for reliability.

Before turning off turbo-charged engine (at least Diesel) driver should wait 30 - 120 seconds before shut down to cool down turbo. Depending on the engine load. Assuming that Prius does it's best to fully load engine (and turbo this way) - engine should be idling before every stop (and waste fuel).
The same goes on highway/freeway driving. After long span of high speed driving (ie. 60 mph) Prius shuts down engine immediately when slowing down. Using turbo - engine should wait for some time to cool it down.

And (from my wallet point of view/TCO) I don't want car that has complicated turbo-engine (with all problems associated with it - replacing turbo, cleaning intercoolers, higher cost air filters and so on), direct injection with complicated head (higher cost to repair) combined with reliable but high cost electric path.

On the other hand I would like to see 10% continous power increase over 3rd gen (110 HP from petrol engine + 30 HP continous / 40 HP peak from battery).
Maximum speed of 180 kmh / 112 mph is OK for me. I'm not using it most of the time but I feel better if I have some margin.

They could install a M62 or M64 Eaton blower on the motor easily. 15 psi boost should do just fine No need to do an idle cool-down with that.

Mike

I would assme they would do it like ford ecoboost. Ecoboost uses water cooling for shut down, it draws water in, the prius already has an electric water pump. Not a problem, you don't need to idle the engine to cool the turbo charger. The bigger thing is sizing, if you only need around 100hp the ice is already small so no reason for turbo expense from downsizing. The next gen TCH might do well with a smaller turbocharged engine though.

Air filters are not much money I don't think I have ever replaced a turbo. The prius is complicated. I fully expect direct injection on the next model, and you won't need to repair the head anymore than the other lexus with direct injection, which is not at all for the great majority of cars.

The battery only produces 36hp now. I would not expect a big jump. The ice with direct injection could easiliy be down sized and still produce more power.

They already say they have di engines in the lab getting 10% better peak efficiency than the gen III prius engine. I'm sure its a matter of time.

E100 adds some unique challenges that add expense. I did read why flex fuel and california CARB regulations don't go together, which may be why we don't see it on a prius. CARB requires the hardest fuel for SULEV and that is E85. E85 will increase both NMOG with cold starts and evaporative emissions. It maybe that toyota does not want to redesign the cat for E85 SULEV, and the tank and canisters for E85 evaporative emissions. The 13:1 native compression does lend itself to doing well with E85. I am not sure what other parts would be needed for E85, but they are not expensive. It would be great if there was a SULEV for E10 rating, and another one for E85 and let people decide.

I meant cooling oil film in turbo bearings not water cooling engine. Talking about cost of turbo replacement - I'm talking about problems with european high power, small displacement Diesel engines. Used strictly in city are not the most reliable in terms of turbo. Friend of mine replaced two units in his Scenic. It's not uncommon failure (among different makers) in hard city conditions. Thats why I'm sceptic to turbo charger in city car. On the other hand - turbo units in gasoline engines are less loaded. I think that mechanical charger would be better especially in low RPMs Prius engine works most of the time.

I think you don't understand the current tech. Ford uses water to cool the turbo, and it draws the water, making it safe to turn of the engine right away. I would assume toyota would use a similar method if they were to turbo charge a hybrid ice.

If you look at say the bmw 2L Turbo, it works from very low rpm, giving a flat torque curve from 1250 RPM . I would expect a turbo like that in a hybrid application. It makes the peak efficiency at low revs, but will become inefficient at high revolutions. Materials have changed and gasoline turbocharging for these cars is not a heavy load at all. Remember also for a prius city conditions are not hard Once the engine is at proper rpm its likely the valve closing would be late making it a miller cycle engine in the most efficient regions which is not full load.

In the lab toyota claims they have a di engine running at 42% efficiency and a turbo di running at 43% efficiency, compared to the current 1.8L Atkinson at 38% peak efficiency. The problem with dropping a turbo in a prius, is it would need to be very small displacement, say 1L to have proper efficiency at the hp range the car needs. VW does cylinder deactivation on their 1.4L 4cyl, but deactivated cylinders have a drop in efficiency too. That's why I would assume a normally aspirated di engine with either atkinson or multimode valving.

I think I heard somewhere that a pseudo Atkinson cycle engine isn't as efficient at higher RPM, that is why they upped the engine displacement from 1.5L to 1.8L for the 3rd generation regular Prius, so average RPM would be lower I guess. In that case reducing displacement won't yield more MPG but again I'm not sure about my pseudo-Atkinson efficiency range.

Going from 38% to 42% is a nice jump, that means around 10% more fuel economy (.38*1.1 =~.42), nice.

I suppose they are researching HCCI engines too but I haven't heard any news of it.

Is the PHEV Prius any higher?