• Jan 14th 2008 at 3:31PM
  • 27
We've been hearing about Honda's upcoming clean diesel for quite some time now, and the automaker was kind enough to show a cutaway of the i-DTEC clean diesel for us at the 2008 Detroit Auto Show. Expect to see the engine appear first in an upcoming and unnamed Acura product around 2009 - but while you may have to wait over a year for the engine, you can see some cutaways of it right now in our photo gallery below. Click past the jump for some brief commentary on what we learned about Honda's i-DTEC clean diesel in Detroit.

Up top, we find centrally-located injectors that are surrounded by four valves - no surprise. Note the extremely tight valve angle, and the roller-equipped rockers that enable this geometry. Valve lash is controlled via the small plungers that appear on the outside perimeter of the head, opposite the valves.

The common rail for fuel is shown at the bottom of this photo, with individual feed pipes to the injectors. We are currently unaware as to what injector technology is being employed by Honda, but various presentations by Denso have us believing that it's likely piezoelectric technology, with multiple pre- and post-combustion injection events utilized to reduce emissions and noise.

The bottom end is smaller than what we're used to seeing on diesels, but then again this isn't a 6+ liter monster intended for a heavy-duty pickup. The piston skirts are considerably longer than what we'd see on a spark-ignition engine of this size, and the top piston ring is located quite some distance from the piston crown (this improves the strength of the piston and helps prevent the ring from getting pinched in its groove during the incredibly high peak pressure of diesel combustion).

Shockingly enough, we saw no evidence of variable-vane technology employed on the turbocharger. Perhaps this is intended to reduce cost?

An electromechanical exhaust gas recirculation (EGR) valve is used to regulate the amount of exhaust gas that is allowed back into the intake manifold. Such gas is inert; when combined with the intake charge during part-throttle operation, it helps reduce the amount of free oxygen in the combustion chamber. This, in turns, helps reduce the formation of oxides of nitrogen (NOx) - one of the nastier by-products of diesel combustion.

Tucked underneath the intake manifold is the EGR cooler, which, as the name implies, takes the hot exhaust gases and cools them considerably before recirculating them into the intake manifold. Diesels employ far greater volumes of EGR than do gasoline engines, so cooling becomes important to avoid excessively high charge air temperatures.

Typical for modern diesels, an electronically-controlled throttle butterfly is placed in the intake tract. It's not for controlling the engine's speed, however; instead, it creates a bit of vacuum to help draw EGR gases into the intake manifold.

Immediately after leaving the turbocharger, exhaust gases are subjected to an oxidizing catalyst to turn hydrocarbon and carbon monoxide emissions to carbon dioxide. Particles that make it through the oxidization process are captured by the particulate filter. This particular filter shows no provisions for a burn-off mechanism; we're not sure if this is a production-intent design and how maintenance-intensive the device may be.

This downstream emissions device would appear to be a lean NOx storage catalyst, which is employed to capture, store, and reduce oxides of nitrogen before they enter the atmosphere. NOx is stored during lean modes of operation; on occasion, the engine runs rich to provide the catalyst with an opportunity to reduce the nitrates to inert nitrogen.

According to manufacturers and suppliers, this approach makes sense on small diesels where the fixed cost of a complex urea injection system is cost-prohibitive. At some point, engine size (and thus catalyst size and cost) increases to the point where urea injection is cheaper.

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    • 1 Second Ago
      • 7 Years Ago
      How will this new DTEC stand up to the Gemans new Diesels. Does Honda have lots of experience building diesels?
      • 7 Years Ago
      Val, you're not quite correct, perhaps you should go work at a refinery. not all refineries produce asphalt, feedstocks for plastic are shorter hydrocarbons than diesel not longer, only about 25% of a bbl is gasoline the rest is diesel , jet, and heavier. cat crackers and hydro crackers break the light atmospheric gas oils heavy atmospheric gas oils, light vacuum gas oils heavy vacuum gas oils and diesel range oils into gasoline range, light cycle oil, intermediate cycle oil, and heavy cycle oil. the catalyst is chosen to yield best results to gasoline and the lessor 3. what's left from the vacuum tower goes to a coker where it is cracked under high heat and moderate pressure to gasoline, light cycle oil and lighter.

      with the cat cracker, hydro cracker and coker the yield of gasoline from a bbl of crude rises to nearly 60%. in europe the catalyst in their cat crackers and hydro crackers is chosen to crack to diesel range hydrocarbons and not gasoline.

      so with this in mind it doesn't take twice as many bbls to make a bbl of diesel, you just have to select your catalyst to crack to what you want. we want gasoline so we crack some diesels to gasoline, in europe they crack to as much diesel as possible and hence have a greater cetane number than we do.

      • 7 Years Ago
      Kotse - Do you think there is a SINGLE PERSON who is going to cross shop a 335d with a Honda accord?
        • 7 Years Ago
        Well, yeah if you're shopping soon for...4DR SEDAN DIESELS!
      • 7 Years Ago
      I'm starting to lose faith that we'll see diesels in the US soon. Wasn't it this time last year that manufacturers claimed by 2008 new diesel engines would be for sale in the US? I remember reading a few months ago that VW pushed the release of its Jetta TDI to 09+. What's the big hold up here, we have the ultra low sulfur diesel gas but none of the engines! Aren't these engines already in use all over Europe?
        • 7 Years Ago
        Two words: California Emissions
      • 7 Years Ago
      I am surprised that Honda would show such revealing cutaways in Detroit Rock City. Are they not afraid of the minions of The General?

        • 7 Years Ago
        Considering the General's track record when it comes to learning and then implementing that which they have learned, I doubt Honda is worried. The General has been tearing down Honda and Toyota vehicles for years, but the results of their labors have proved fruitless, or clueless.
      • 7 Years Ago
      Put this in the current TSX and it might have swayed me from buying my MB C230 (which I wanted a diesel with in the first place). But way to go EPA and DOT for banning me from what I want to buy.
        • 7 Years Ago
        The reason VAT is lower on diesel is to provide a leg up for the diesel auto- and engine makers who are, you guessed it, primarily European. It's essentially is (or was, between engines like this and Toyota's newer C4Ds) a discouragement of Asian models, which were primarily gasoline-powered.

        It's telling that diesel tax rates (and marketshare) are much lower in countries that don't play host to diesel manufacturers. Look at Switzerland, for example: diesel doesn't enjoy nearly the tax advantage it does in Germany, likely because the Swiss government isn't lobbied to heck by VW/MB,
      • 7 Years Ago
      What you wanted to buy polluted too much. I know this is tough for people, but:
      * Good Fuel Economy does not equal low emissions
      * Low emissions do not equal good fuel economy
      * Not all emissions are greenhouse gases
      * Not all greenhouse gases are immediately harmul to people
      * Carbon dioxide is not the only emission to worry about

      I don,t care I'm buying a diesel car anyway.
      • 7 Years Ago
      Does anyone know what the redline is on this thing? I'll trade in my Si if it's at least in the 7000's.
      • 7 Years Ago
      Diesel burns at a higher temperature no (no spark plug)? It make sense that they didn't go veriable turbo the material cost too much. Borg Warner makes or invented em no?
        • 7 Years Ago
        Honda uses variable turbo in the european 2.2 CDTi, offered in the Accord and Civic.
      • 7 Years Ago
      I appreciate that two of the things they added to the cutouts were the emissions control mechanisms. Honda appears to be shouting "It won't be sooty, dangit!"

      I thought that in some cases you could tinker with the exhaust gas temp to start the burn-off with the particulate filter. Then again it might just collect in a drum like used toner on a printer...
      • 7 Years Ago
      Gm copy this, no problem, its been out for 3 years in Europe. (ok, maybe its a bit different for usa)

      I'm a Canadian, Drove Gas for all my life, until I moved to europe in 2001, I had a 2005 Honda Accord Executive Touring 2.2 diesel for 3 years (got the first one on the lot back in December 2004.

      The Executive is a TSx Wagon, with all the nice little addon's.

      About the engine, I can tell you over there on the other side of the pond, your going to LOVE this engine.
      BUT, your going to have to LEARN how to use it.

      Its got a redline of 4500rpm, but all the Power is from 2200 to 3400rpm, its not all up Top like a Gas engine.
      Plus, if you want Power, you got to be "On-The-Turbo"

      I drive about 135-1x0 (80+mi/h) every work day, for about 20 minutes home and back. I am currently getting about 42-47mpg us. (average about 800km/52l)

      So, welcome to the Diesel clube America! hope you enjoy it!

      Now my Question to Honda, We here in Europe are waiting for something NEW!!! how about a hybrid Diesel :-)
      • 7 Years Ago
      Or all automakers can quit investing all their money in diesels and invest 100% of that money in HCCI engines! Then we can have gasolines horsepower and acceleration with the efficiency of diesel at low loads and save mass because you won't have to make a reinforced block!
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