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One of the keys to making the latest generation of diesel engines as clean and efficient as they are has been common rail injection systems and, more recently, piezo electric injectors. Continental Automotive Systems has just introduced a new type of piezo injector that may take diesels to the next level. Earlier injectors used electro-magnetic solenoids to move the injector needles allowing fuel to flow into the combustion chamber. Piezo injectors use a stack of piezo crystal plates that expand when an electric current is applied. That expansion causes the needle to move. The expansion of the piezo crystals is more precise and repeatable than the electro-magnetic solenoids allowing for more precise fuel metering for lower consumption and emissions.
Continental's new injector design takes advantage of the precision and reproducibility of the piezo crystals by adding position sensing to the needle itself. Because the position of the needle in time now correlates so well to the fuel flow rate, the potential exists to be able to eliminate other sensors that are being used to control diesel fuel systems. High pressure common rail injection systems typically use 5 -7 individual injection pulses per combustion cycle. Because the fuel flow can be measured in real time with the new injectors, the size of individual pulses within the sequence can be varied for even lower fuel consumption and emissions. Continental is claiming the new injectors help achieve a 35 percent reduction in particulate and NOx emissions. An engine optimized for these injectors could potentially meet the Euro VI (and equivalent US Tier 2 Bin 5) standards without the need for any costly NOx aftertreatment. This would help cut the cost premium between gas and diesel engines.

[Source: Continental]


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    • 1 Second Ago
  • 9 Comments
      • 1 Month Ago
      Sam, the combustion temperature is high because of the rapid fuel burn. How an injector can make fuel burn slower (and thus cooler) is beyond me.

      The only way I know to make fuel burn cooler is to put too much in, which reduces heat due to the energy taken up for fuel atomization.
      • 6 Years Ago
      Actually the NOx is primarilly a result of combustion temperature. If the temp is kept low enough little or no NOx is generated. Precise metering of the fuel allows the combustion temperature to be regulated reducing NOx production.
      • 1 Month Ago
      NOx levels are a result of combustion temperatures. The temperature is dependent on compression ratio, the amount of fuel combusted and the air fuel ratio. The higher compression ratio the higher the potential combustion temperature and thermal efficiency of the engine. The amount of fuel burned is the amount of heat input into the engine which affects temperatures. The air fuel ratio is also a major contributer to NOx formation. Engine temperatures peak at a slightly lean mixture. As the ratio gets more lean or rich, the combustion temperatures lower reducing NOx but also combustion efficiency. Going rich is bad because then you get unburned hydrocarbons and other bad emissions. By going lean, the peak temperatures are lowered because excess oxygen and nitrogen are present consuming energy lowering temperatures keeping NOx from forming. The amount of nitrogen in the engine is dependent on the quantity of oxygen present. For every mole of oxygen there is about 3.76 moles of nitrogen. The new ultra low emission vehicles run very lean requiring unique designed to be able to get the fuel to combust. With these injectors, the quantity of fuel used can be more precise allowing the engine to be able to run very lean which reduces NOx.

      The rate of fuel burn depends on the type of fuel and the speed of the engine. As the speed increases, there is more turbulence in the engine increasing burn speeds but does not effect NOx.
      • 1 Month Ago
      The way I see it, it has less Nox emissions because it uses less fuel? Less fuel, less Nox?
      • 1 Month Ago
      While piezo injectors can support up to 7 injections per combustion cycle, in practical applications only 2-3 are used.
      • 6 Years Ago
      That would be amazing. But I don't see how this can be. NOx comes from the fast burn ("knock") inherent to Diesel combustion. It happens even with the exact right amount of fuel in the chamber.
      thanhma77
      • 6 Years Ago
      Interesting new piezo electric-fuel injector design...

      Controlling the fuel flow does have an affect on engine performance.

      Most engine tuners upgrade their fuel injectors to pump more fuel into the engine...with Continental's new injector design their approach is to save gas, lower fuel consumption and emissions.

      Interesting article.

      • 6 Years Ago
      I hope they hold up better than Navistar's injectors.
      • 1 Month Ago
      Thats pretty hot