|Exhaust gas recirculation is very important on a diesel engine to reduce NOx emissions. This works by introducing exhaust gas into the combustion chamber which acts like a neutral buffer inhibiting combustion. In a diesel such a large amount of EGR is used that it must be cooled so it won't effect expansion and reduce power. This water cooled heat exchanger is the EGR cooler.|
You are probably curious on how the Skyactiv D drives. We were able to sample a couple prototype engines in some heavily disguised 2012 Mazda 6’s on a short drive. Although these cars were very early mules, we did get a chance to put a decent amount of miles on them over a variety of conditions.
|The exhaust side of the Skyactiv D engine is very busy. You can see the twin sequential turbos and the large cannister for the ceramic particulate trap. The engine burns its fuel very cleanly so exhaust after treatment and NOx trapping catalytic converters are not required.|
The diesel engines were quick to start when cold and felt peppy even though Skyactiv magic was probably going on with the cam timing. The only hint that a diesel engine was under the hood was that you could hear a muted diesel clatter. Surprisingly this went away almost completely as the engine warmed up making this the most refined diesel we have ever experienced. A Golf TDI is noisy compared to the Skyactiv D.
|Check out how small the exhaust housing of the low speed turbo is. Diesel exhaust is very low energy compared to a gas engine so the turbo has to have a real small A/R to spool quickly.|
What impressed us was the performance. The engine put out gobs of torque and it was no problem to lay rubber with both the six speed manual or the six speed automatic. The engine revved willingly past 5000 rpm, a full thousand more than our project TDI, feeling almost like a peppy gasoline engine. This was no weaksause hybrid for sure. The Skyactiv D was fun with the six speed and best suited with the automatic where it could put torque through the slushbox with ease.
|What? A throttle body on a diesel? The throttle body does not control engine speed. It is actually there to help regenerate the particle trap. During the trap's regeneration cycle it partially closes which results in more exhaust gas being retained in the cylinder due to the intake opening exhaust cam, greatly boosting exhaust gas temperature. This helps burn off the carbon particles trapped in the particle trap more quickly.|
Listen Mazda, this is what MotoIQ readers will want. Ditch the big heavy Mazda 6 and put the Skyactiv D in the small and lightweight Madza 3. Call it the Mazdaspeed eco killer or something. It would be a sub 6 second zero to sixty, 14 second quarter mile sleeper that will get nearly 50 mpg. Sign me up. I will buy one right now, maybe even two of them! Green weenies throw your Prius in the trash or race me for pinks and I will do it for you.