Mazda introduces HAZUMI concept along with new 1.5-liter SKYACTIV-D diesel
05 March 2014
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| HAZUMI. Click to enlarge. |
Mazda unveiled the HAZUMI next-generation subcompact at the Geneva Motor Show. Mazda is focusing on four key areas with its new generation models: KODO—Soul of Motion design language; SKYACTIV technology; Mazda Proactive Safety; and a new car connectivity system called Mazda Connect. (The name Mazda Connect is used in Japan, US, Canada and Mexico. The system is referred to as MZD Connect in other markets.) The MAZDA HAZUMI brings together all four of these elements and foreshadows Mazda upcoming next-generation subcompact car.
The MAZDA HAZUMI marks the world premiere of the SKYACTIV-D 1.5. This compact and lightweight clean diesel engine is designed for combustion efficiency, just like the larger displacement SKYACTIV-D 2.2. (Earlier post.) It offers ample torque and dynamic performance which is linear right up to the top of the revolution range, and below 90 g/km CO2 with the Mazda HAZUMI. It will also fulfill stringent Euro 6 requirements without aftertreatment systems such as a NOx trap or selective catalytic reduction.
The 5-door HAZUMI hatchback is also equipped with the SKYACTIV-DRIVE (6AT) transmission; the i-stop idling stop system; and the i-ELOOP regenerative braking system.
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| SKYACTIV-D 1.5. Click to enlarge. |
Conventional diesel engines generally have a high compression ratio; hence, the compression temperature and pressure at piston top dead center (TDC) are extremely high. When fuel is injected under these conditions, ignition takes places before an adequate air-fuel mixture forms, causing localized heterogeneous combustion, resulting in the formation of NOx and soot, Mazda says.
The advent of stricter emissions regulations leads to a delay in combustion until after TDC (with a lower cylinder pressure and temperature), although this causes fuel economy to worsen.
The SKYACTIV diesels feature a low compression ratio of 14.0:1 (low for a diesel); reducing the compression ratio in the diesel decreases the compression temperature and pressure at TDC. Consequently, ignition takes longer even when fuel is injected near TDC, enabling a better mixture of air and fuel.
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| Top: High compression diesel ignition occurs before the fuel is sufficiently mixed. Local hot spots cause NOx and over-rich spots cause soot. Bottom: Lower SKYACTIV-D compression gives more time to mix before ignition. The result is cleaner combustion with low NOx and soot emissions. Source: Mazda. Click to enlarge. |
To realize ideal combustion timing and duration as well as clean emissions at the same time, Mazda uses this premixed compression ignition combustion by controlling ignition timing based on model-based prediction of ignition delay in the low compression ratio engine.
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| SKYACTIV-D Technology Concept. Source: Mazda. Click to enlarge. |
The formation of NOx and soot is alleviated since combustion becomes more uniform without localized high-temperature areas and oxygen insufficiencies, Mazda says. Furthermore, injection and combustion close to TDC make a diesel engine highly efficient. The expansion ratio (or amount of actual work done) is greater than in a high-compression diesel engine.
Also due to the low compression ratio, the SKYACTIV-D diesel engine also burns cleaner, discharging far fewer nitrous oxides while producing virtually no soot. It can thus do without NOx aftertreatment and still meet emissions standards globally.
Furthermore, the lower compression ratio enables a reduction in weight through structural optimization and in mechanical friction in the engine.
Two main problems have limited the spread of low-compression-ratio diesels: the first is starting during cold operation, and the second is misfiring during warm-up due to the lack of compression temperature and pressure.
To address these issues, Mazda uses new 12-hole piezo injectors which allow for a wide variety of injection patterns; precise injection amounts and timing increases the accuracy of mixture concentration control, providing cold start capability. The SKYACTIV-D injectors are capable of a maximum of 9 injections per combustion.
Along with three basic injections—pre-injection, main injection, and post-injection—different injection patterns will be set according to driving conditions.
Misfiring is avoided by adopting a variable valve lift (VVL) system for the exhaust valves. The exhaust valves are opened slightly during the intake stroke to recycle host exhaust gas back into the cylinder, increasing the air temperature. The elevated temperature stabilizes ignition.
SKYACTIV-D also uses a two-stage turbo in which one small and one large turbo are selectively operated according to driving conditions. This is intended to achieve high torque and response at low speeds, and high power and high speeds.
However, Mazda North American Operations is delaying the introduction of the SKYACTIV-D 2.2 in North America from the original targeted Spring 2014. Mazda said that the although the SKYACTIV-D can meet emission regulation requirements without the use of a NOx after-treatment system, it decided that further development is required to deliver the right balance between fuel economy and “Mazda-appropriate” driving performance. (Earlier post.)
This EMP approach to low compression ratio has many advantages, but not sure if it eliminates the poorer fuel economy associated with low comp diesel by old school mechanics.
Presumably it and other EGR type strategies don't compromise economy.
Posted by: Arnold | 05 March 2014 at 10:46 AM
The Mazda low compression diesel uses a partially premixed combustion (PPC) approach similar to earlier research by Bengt Johansson of Lund University. This actually increases thermal efficiency. Similar concepts include the RCCI gasoline diesels of Rolf Reitz and the Hyundai/Delphi Gasoline Direct Injection Compression Ignition (GDCI). These processes slow the ignition process by using premixed compression ignition combustion and allow either lower compression ratios or fuels that are more resistant to auto ignition e.g., low-cetane diesel or gasoline.
In addition, this reduces the cost of making diesel engines since lower pressure fuel systems are also used that are like the widely adopted direct injection spark ignition fuel systems. Further, this means that with the reduced cost of these engines, hybrid technology can still be added further improving fuel economy.
Posted by: gryf | 05 March 2014 at 12:15 PM
The 1.5 diesel looks perfect for Europe where small diesels in small-medium cars are very popular.
If it gets 90 gms/km, it will be in a very low tax band.
They might want to sell the engine to other manufacturers.
Ford used to be friends with Mazda - I wonder would they take it?
Posted by: mahonj | 05 March 2014 at 12:17 PM
Sounds good, but if this technology works so well why has Mazda now delayed the Mazda 6 Diesel for the US market by over a year? The delays are supposedly due to emissions problems, so it is related to the present article.
Last I heard, months ago, Mazda 6 was supposed to arrive this spring, 2014.
VW and Audi have done a considerably better job with clean diesel than Mazda. Step it up, Mazda!
Posted by: Jus7tme | 07 March 2014 at 06:16 PM
I did a search
http://www.autoweek.com/article/20140109/carnews/140109861
QUOTE:
If you've been waiting for a Mazda 6 diesel, prepare to wait a bit longer. After delaying the U.S. launch until Spring 2014, Mazda now says it won't meet that target date, either.
Mazda says the engine meets current emissions standards using only a particulate filter, but the resulting blend of performance and fuel economy isn't up to snuff. Company spokesperson Jeremy Barnes put it simply: "We can meet the emissions standards today, but not with the kind of performance worthy of a Mazda badge." Mazda is reportedly working on a solution, exploring all options, including exhaust aftertreatment, as it seeks the proper economy/entertainment blend.
Posted by: Jus7tme | 07 March 2014 at 06:18 PM