Why gasoline turbocharged direct injected engines?
by Sam Abuelsamid on May 28th 2009 at 11:53AM 
Hybrid and battery electric cars get most of the attention from drivers looking for more efficient transportation. Toyota has done a masterful job of marketing the benefits of hybrids and, for a great many people, hybrids are an excellent means of saving on fuel and reducing emissions (not everyone, though). The trouble is that hybrid systems add hardware, cost and a lot of complexity, especially for the control systems. While Toyota and Honda have done an admirable job of reducing the cost of their respective hybrid systems, the fact remains that a hybrid will always be more expensive to build than a similar vehicle with only one powertrain. For battery electrics, the problem is compounded by the stubbornly high cost of batteries.
One way to make a significant dent in overall fuel consumption is for a substantial portion of the new vehicles sold every year to be significantly more efficient. Getting there means using technologies that are cost effective. In an automotive landscape where U.S. sales have collapsed from 17 million annually to less than 10 million, automakers are looking for ways to sell more efficient vehicles that people can afford to buy. That's why gasoline turbocharged direct injected engines are one of the more popular choices coming over the next several years. Learn more after the jump.
GTDI engines are relatively new and offer a number of benefits that can help achieve some of the gains in fuel efficiency required by regulations, economics and the environment. Turbocharging, of course, has been around for decades and gained significant popularity in the early to mid-1980s. At that time, automakers grappled with then-new CAFE regulations and sought to use smaller displacement engines with turbochargers to replace larger engines.
Unfortunately at that time, engines still used carburetors and electronics were primitive. Drivability and durability issues eventually sent turbos to the back burner for a time. The idea of the turbocharger is to harness some of the thermal and kinetic energy in the engines exhaust gases to pump more air into the engine. More air and fuel means the engine makes more power. However, engines typically only require peak power output a small fraction of the time they are operating. A vehicle that uses a large displacement engine is capable of providing the peak power needed for acceleration or hauling, but also has mass to lug around all the time, weight that is often not being used.
Using a four cylinder engine in place of a six or a six in place of a V8 means the engine is lighter and more efficient. It also means the engineers don't have to build in as much structure to support it. There is a cascading effect of efficiency and mass reduction that can happen. Another benefit is that this mass reduction can come without having to resort to expensive and energy intensive materials like composites or even aluminum.
Let's get back to the engines now. Since drivers typically only use a fraction of the peak output of an engine, a smaller displacement unit can operate in more efficient region for most driving. The addition of a turbocharger allows the production of on-demand power for climbing grades and merging on freeways. The downside of turbos in the old days was knock. When air or any other gas is compressed, the Ideal Gas Law tells us that the temperature will rise. Compress the air enough and the fuel that is mixed in will spontaneously combust.
In the '80s, engineers tried to address this by spraying water into the compressed mixture to cool it before it entered the combustion chamber. Obviously, this adds complexity and the water tank has to be regularly re-filled. Enter direct injection. In the days of carburetors, the air and fuel were often mixed further upstream and compressed together allowing detonation. Now that fuel can sprayed directly into the combustion chamber, the turbo compresses only air and pumps it into the cylinders.
When the fuel is sprayed in, the hot air vaporizes the fuel and the process actually reduces the temperature of the mixed charge in much the same way water injection did. The result is that modern GTDI engines can run with higher levels of turbo boost and higher compression ratios with less risk of knock. More boost and compression mean higher torque output from the engine. Thus, smaller displacement engines can produce more torque at lower rpms resulting in better drivability. With this kind of engine behavior, drivers feel less need to rev the engine to get the performance they expect and fuel efficiency is improved. Direct injection also has an immediate impact on efficiency and emissions by more precisely metering fuel and leaving less unburned fuel going out the exhaust.
Finally, turbo direct injected engines are also particularly well suited to operating on ethanol. Since the alcohol only has 60 percent of the energy density of gasoline but a much higher octane rating, the boosting and direct injection allow engines to run at higher boost, overcoming the power deficit while nearly equaling the efficiency of running on gas.
The bottom line is an improvement of 15-20 percent in efficiency over a comparably powerful normally aspirated engine of larger displacement. Drivability is improved and the cost premium is smaller than other technologies. It's estimated that Ford's new EcoBoost V6 costs about $700 more than the standard 3.7-liter V6 while making the power of a V8. Volkswagen Group has already been offering a number of GTDI engines for several years as have Mazda, General Motors and others. Ford is making the biggest mainstream GTDI push starting this year and promises to have its EcoBoost engines available in 90 percent of its cars within four years.
Following the V6 EcoBoost, a 1.6-liter four cylinder version goes into production in the UK late this year and a 2.0-liter will follow likely later in 2010. An even smaller 1.2-liter engine should launch within the next two years. GTDI is certainly not the end game by any means, but it is an important interim step for mainstream improvements in efficiency until battery prices come down.
Reader Comments (Page 1 of 2)
NHG 12:03PM (5/28/2009)
Go Ford...
Reply
Clay Garland 12:40PM (5/29/2009)
My 1987 Regal gets 26MPG, and could do 60 in under 5 seconds. In '87. I think automakers are just now realizing what the cheap gas of the 90's did to our perspective. Think if Buick had continued development of the turbocharged engines with fuel economy in mind.
gorr 1:26PM (5/28/2009)
I have said and i must repeat to make a gazeous ice with theses technologies. Gazeous hydrogen is more difficult to inject and calibrate in operation then the old air-fuel gasoline ratio of yesterdays. Theses dinausors ( gm, ford, honda, toyota, ferrari, porsche, aston-martin, fiat, lamborgini, buggati, tata, etc) must leaves. They only and exclusively sell outdated, costly, underperforming, polluting, subsidized, worshipped, marketed, protected by billions of ignorants so called car-guys, ice gasoline cars and lawnmowers.
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Matt 1:58PM (5/28/2009)
What are you talking about? Nobody can understand what you're saying. Gaseous ice? I think you have your states of matter mixed up man. Solid, Liquid, Gas, Plasma, that's it so far as I know.
James 2:09PM (5/28/2009)
Maybe gore means Internal Combustion Engine when he says ice.
Matt 2:26PM (5/28/2009)
Oh yeah, ICE, could be. Gorr, use all caps for abbreviations please... especially if it follows a misspelled state of matter to avoid confusion.
Gaseous H2 combustion is convenient because it uses a lot of mature technologies that are the same in gasoline engines (or builds on them), but I'm not convinced it's any more efficient than a fuel cell. We'll see though, BMW is working on it pretty hard.
usbseawolf2000 1:47PM (5/28/2009)
" the fact remains that a hybrid will always be more expensive to build than a similar vehicle with only one powertrain."
Always? I doubt it. A full hybrid has the HV battery pack but not a mechanical gearbox. It has extra electric motors but not starter, alternator, belts or chains. Next generation HSD may cost the same as non-hybrid and could be cheaper in subsequent generations.
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PowerCell 2:03PM (5/28/2009)
"Always? I doubt it. A full hybrid has the HV battery pack but not a mechanical gearbox. It has extra electric motors but not starter, alternator, belts or chains. Next generation HSD may cost the same as non-hybrid and could be cheaper in subsequent generations."
There's so much wrong with this, I don't know were to start...
Matt 2:13PM (5/28/2009)
You're mostly right, but the belts are not a factor, that's just the way Toyota chose to do it so they could shut the engine down completely and is not part of it being a hybrid per se. Plus, for every belt they eliminate they have to replace that belt with an alternative power source (a small electric motor). You forgot to mention that they replaced the timing belt with a chain, the added a control computer for the Power Split Device, the planetary gears in the PSD that spin extra fast, and the fact that those two Motor/Generators are much larger than any starter or alternator. How about extra cooling for the two hot electric motors or the fact that only a specially trained Toyota technician can fix the thing if it breaks? What about the amps that tie the battery pack to the motors and the computer?
I know I'm getting knit-picky, but these things add up, and regardless of how "simple" the PSD seems in a diagram, it really is more complex than your standard drive train, and even if there were fewer parts (which there aren't) complexity is expensive.
That said, the price of electronics has a continuing trend. They get cheaper over time as technology adapts and consolidates the processes. If that trend continues hybrids should get cheaper and easier to make. One day the sum of the electric bits will surely be less than the sum of the mechanical ones they replace, we're just not there yet.
usbseawolf2000 3:23PM (5/28/2009)
PowerCells: Start by learning more about HSD.
Matt: Agree. There are other things I can add to the "knit-pick" list that sway the other way. The brakes are smaller and lasts twice longer due to regen-brake. The gas tank is smaller. Gas engine is smaller. 12V lead acid battery is smaller (1/3). No pulleys.
MG2 is air cooled. MG1 is liquid cooled by the same radiator. Owners are able to fix and rebuild using repair manual and community input. See this thread: http://priuschat.com/forums/prius-main-forum/51021-i-just-acquired-new-project-vehicle.html
Rich 4:16PM (5/29/2009)
Erm, I think by "full hybrid" you mean "full electric", or EV. Look up "hybrid" in the dictionary, would you? And learn how to reply to others' comments while you're at it! Sheesh!
usbseawolf2000 4:26PM (5/29/2009)
Rich:
See more info for hybrid types: http://john1701a.com/prius/hybrid-types_print.htm
Brad Stone 10:41AM (6/01/2009)
Yes, always. It's a simple comparison:
engine -> engine
transmission -> powersplit
?? -> Large, heavy battery with computer
The elimination of the alternator, a smaller 12V battery, and a smaller fuel tank will never make up for this difference. Compared to a several-thousand-dollar battery pack these are essentially free. And for those who think the battery pack price will come down significantly any time soon, you're dreaming. Have you bought a pack of Duracell's lately? That technology has been around for decades and it's still relatively expensive. Add to that the fact that the batteries (at least currently) are being made with rare materials and you won't see any relief any time soon.
usbseawolf2000 11:25AM (6/01/2009)
Instead of the traditional transmission, the "hybrid transaxle" consists of two electric motors and a power split device. This hybrid transaxle performs more than the transmission's job. It also assumes the job of the alternator, starter, half of the propulsion/powertrain and half of braking. How much cost reduction do you attribute those?
HV battery price for 2003 Prius was $2,985. Last year, Toyota dropped it to $2,299. That's 23% drop in 5 years. The warranty is 8-10 years and the pack does not drop dead after the warranty expires. Further mass production would bring the price down by the time you need to replace it, if you still want to. Who would put a brand new engine in 10 years old car anyway? The sames goes for the HV battery.
Remember, steel contains 6% of Nickel. 3,000 lbs steel would have 180 lbs Nickel. The Nickel in the Prius battery is about 23 lbs, 11% Nickel of the entire car. If the price of Nickel goes up, the cost of the entire car would go up as well.
jzj 1:59PM (5/28/2009)
Good article. Perhaps more could be said of DI's ability to allow improved metering over a range of rpm and conditions and therefore crank out greater efficiency in all uses. While I do not know this for certain, it would seem that DI relieves the need for expensive variable valve timing and is therefore a bit cheaper in that way. I see little reason why DI needs to be much more expensive in given the tradeoffs it allows -- it requires better sensors, better fuel pump and fuel lines, better injectors, turbos, and perhaps better computer hardware, but you have a smaller engine and less material all around. I wonder if the software can map for E85 and, assuming the engine internals are strong enough, really crank out some horsepower with high turbo boost.
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yh 3:22PM (5/28/2009)
people are doing the remap to E85 now, its just a matter of making sure your fuel plumbing can handle the high alcohol content (most cant in stock form). Unfortunately, E85 results is worse gas mileage (less energy/liter) but does allow for more power (its like running 100+ octane gas). Im not sure of any DI engines that have been remapped for E85, but I know the Subi crowd has been doing it for a while now with the WRX/STi.
augustus 3:17PM (5/28/2009)
I'd love to see how a smaller DI engine with its higher torque and better torque curve could be used in a hybrid. You might be able to get some really nice freeway mileage.
usbseawolf2000 3:36PM (5/28/2009)
augustus: Unless a downsized turbo-charged ICE produces less emission, you won't see it in hybrids. Well, at least the "green" variances. I am sure a performance hybrid which disregard emission issue may be built but unlikely due to government emission regulations.
augustus 3:51PM (5/28/2009)
@ USB
Ah what I was wondering was if the higher torque at low RPM could be leveraged in a hybrid to gain better fuel efficiency for the real highway speed limit here in CA: 70-80 mph. People like myself with long highway commutes won't drive slower unless there is traffic or a police car behind us :)
In the end the Jetta TDI just looks better and better for commuters who drive long distances at 70 mph.
-Side note: I'd love to see the curve for MPG/MPH for these cars and I think that would be more useful for picking a car than the current EPA numbers which are gobbledy-gook.
jzj 5:08PM (5/28/2009)
Given that due to MPG and emissions directives most all manufacturers are likely to go the way of hybrids in the relatively near future (say, in 5 years), what interests me the most is the future of engine design to mate with hybrids. Obviously with serial hybrids that run their engines at a steady state, none of this is necessary: just design a simple engine that works great at one speed (this may be HCCI, TDI, or otherwise, but but it will focus more on being light, simple, and quiet). For parallel hybrids, it's more about adding a bit of acceleration power and providing high-mileage highway cruising, so some rpm flexibility will have to be retained. TDI -- seems to provide a nice balance of torque and steady-state (highway) economy. HCCI -- not so much.