Diesel-engine designers have long grappled with a dilemma: Reducing emissions meant either cutting efficiency or adding expensive equipment. With the Skyactiv-D, Mazda engineers decreased pollution, boosted mileage, and eliminated the cost of exhaust after-treatments by building the world's lowest-compression diesel engine. They then added two turbochargers and a capacitor-based regenerative braking system. When it arrives in U.S. showrooms late this year, the Skyactiv-D–equipped Mazda6 should deliver approximately 44 highway mpg while meeting strict emission standards, proving that diesel engines have many miles left in them.
A two-stage turbocharging system contains a small turbine that boosts low-end torque, as well as a larger turbocharger that increases high-end horsepower. An electronic controller runs the turbochargers, tuning performance to conditions.
The Skyactiv-D's engine overhaul has a side benefit: Engineers were able to build the engine with lighter, lower-friction components, including 25-percent lighter pistons and an aluminum cylinder block that trims 55 pounds.
LOW COMPRESSION RATIO
Diesel engines ignite fuel by combining it with air and compressing it to extremely high pressure. Yet compared to that of gasoline, the high pressure and temperature of diesel combustion produce more smog-forming nitrogen oxides and sooty particulate matter. To meet pollution standards, modern clean diesels delay combustion until the piston begins its descent—but that reduces power and efficiency. Mazda's solution: new fuel injectors and exhaust valves that allowed engineers to lower the compression ratio from 16.3:1 to 14.0:1.
NO EXHAUST TREATMENTS
Before exhaust even enters the tailpipe, the engine's low compression ratio cuts emissions of nitrogen oxides and other pollutants enough to meet present (and future) standards both in Europe and the U.S. As a result, the Mazda6 does away with expensive urea tanks (which drivers have to refill every 10,000 miles or so) that many diesels use to neutralize emissions.
i-ELOOP, one of the industry's first regenerative braking systems to store energy in a capacitor rather than a battery, further improves fuel efficiency. When the driver decelerates, an alternator generates up to 25 volts, charging the capacitor in seconds. Stored energy can supply all electric needs—headlights, climate control, audio system—for one minute. Capacitors have been used to boost power on F1 cars; eventually, they could be used to do the same in passenger electric cars.
Engines: 2.5-liter Skyactive-G gasoline engine (available now) or 2.2-liter Skyactive-D diesel (available late 2013)
Base Price: $20,880
Pretty cool. Compound turbos sounds like it should be a little fast. I wonder what the power output is going to be.
Maybe I am missing the point, but 44 mpg (it was 56 in the RSS feed!?) doesn't sound that great to me. 5.3 l/100km, I easily get that in my 8 year old Toyota Corolla with winter tires and driving fast with no thought of consumption. Normal is 4.2 l/100km, I even got it down to 3.9 l/100km (60.3 mpg).
And that car does not have urea tanks or something like that, and fulfills highest standards today (EURO4).
So what's so special about this engine? Using new techniques to achieve old goals?
"lighter, lower-friction components" - wasn't aware that mass had much to do with friction. But building a diesel block out of aluminum is impressive. Looks like a pretty full sized sedan, so 44 mpg while not spectacular, is still good (and will get better).
Yes it says they're running it on their Mazda 6 which is a high end larger yet sporty (as all mazda's are) sedan. Probably has great size and power to mileage ratios.
I read this article when it was first posted, and it did indeed read 56 mpg. There is no mention of an edit now that it is down to 44 mpg. Come back tomorrow and it'll read 30...
Now if they could only get the price of Diesel fuel down close to gas. It's usually 40 to 50 cents higher than PREMIUM unleaded (if not more). So what good is higher mileage when the fuel costs are about 20% higher than 87 octane unleaded?
"16.3:1 to 14.0:1"
An naturally aspirated engine would require 16 or more to one. A forced induction motor can be reduced to less since the air charge plus compression is then calculated.
Boosted GDI engines will be more widely used for autos than diesels. It has to do with simple economics.
- Toyota holds patents to most of the critical components/algorithms/design of hybrid drivetrains. That's why Nissan just gave up and licensed the Toyota Hybrid Synergy Drive. GM gave up and went with extended range VOLT technology. Honda holds some patents on series hybrids drive trains, simpler albeit a slightly less efficient.
- Everybody else is now SOL in the cold. That's why we can expect to see more of these phony drive train designs as some automakers scramble to meet new efficiency and emissions standards.
Remember when Toyota came out with the first(ugly) Prius?? Everyone laughed and condemned the concept as pointless. They stuck with it for the long haul with a vision for the future. Well, it seems that future has finally come. You cannot design a hybrid drivetrain without violating any number of Toyota's patents on hybrid engine management algorithms. Even little details like how and when the electric engine kicks-in or gas engine turns off. These same concepts will also apply to future drivetrains (Hydrogen, fuel cell, NGV, etc).
Guess Toyota's having the last laugh now.
If you take a close look at the CR's of both the GDI and diesel DI versions of Mazda's Skyactiv engines, you'd note that they are very similar. The optimum CR for either a boosted GDI engine or a boosted DI diesel, seems to be around 14:1.
Of course, with a boosted 14:1 GDI engine you must be concerned about detonation. While with a 14:1 boosted DI diesel, your main concern is getting it to start.
The boosted DI diesel benefits from a low 14:1 CR because it minimizes NOx emissions. And while the boosted DI diesel is more costly to manufacture than a similar boosted GDI engine, it also gives better part load efficiency.
The engine might be well designed, but in Australia and Europe it has been compromized by faults in exhaust treatment solution, which ironically haunts back the engine. The black exhaust smoke is caught by the particulate filter. This filter is purged by heating to high temperature every 200 km. The heating is achieved through an under-engineered solution: send extra diesel fuel through cylinders into exhaust. This is trouble waiting to happen. In case of Mazda SkyActive diesel an undisclosed, but significant number of owners observe dilution of engine oil with diesel fuel. The oil dipstick had a max mark corresponding to 7% fuel content in engine oil. As a solution Mazda is now replacing the dipstick with a new one, having a max mark 11 mm higher and allowing for 14% diesel fuel content in engine oil before the overfilling reaches the max mark. This allowed Mazda to stop sponsoring emergency oil changes at 4000 km triggered by oil level reaching the original low max mark. Now the rising oil level reaches the NEW high max mark only at 10,000 km. Only a fraction of vehicles have the rising oil "feature", others maintain the oil level stable. The phenomenon has no correlation to driving style (stop&go versus highway) or climate (Norway vs Spain). Mazda says this oil level rise is normal, meaning that they do not promise to fix this on vehicles that demonstrate this "feature". They also claim that diesels with particulate filters of other manufacturers have the rise of oil level as well. Now there is a psychosis among the owners of Mazda Skyactive diesels. They measure the engine oil level every 1000 km with a micrometer and compare its behavior with each other on a number of Internet groups.
Is all this research into 'lower polluting engines' justified compared to 'no pollution'?
Mandated 'lower polution' has cost we consumers billions of dollars over the last fifty years because of the associated 'lower mileage'.
How long till we finally have an end to compression engines?Do we have to use up every barrel of fossil fuel before we get something that isn't choking us to death?
Pluggable cars are being re-charged with an 18th century coal-fired, steam-driven turbine down at the local power plant. Mandated pluggables needs to be coupled WITH Mandated Electric generation. This will hurry up the development of new technology so we can be using sunshine, wave power, or wind energy to power AND our cars without air pollution.
Lot of flexibility in the value proposition. Under 50 MPG, big deal - probably stay with my tried and true VW TDi. Over 50 mpg much more interesting. VW runs the diesel exhaust through the oil sump so a major oil change every 10K MILES. If Mazda's "clean burning, soot free" system needs an oil change every 6K miles (10KM) then I am underwhelmed. Was surprised to hear in the comments the challenges this power plant has seen in Australia and Europe. Won't fly if similar experience obtains in the US.
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There is a error made in this article when describing the Diesel method of ignition, the article describes air and fuel as being compressed together to achieve combustion.
In fact what happens in the Diesel cycle is that air is compressed to high pressures and temperatures..... THEN the fuel is injected.
The cycle as described in the article does work but was popular only with model airplane engines and used a variable compression feature in the form of a screw adjustable counter piston to vary the compression ration & allow for "fine tuning" after starting. a form of ether was used in this engine's fuel.