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Simulation of diesel combustion at split injection

 

     Split injection of fuel in diesel is one of the effective way of NO emission decrease. At split fuel supply the injection is divided on 2, 3 and more stages followed step by step. Optimization of fuel fraction in pilot injection as well as optimization of delay between injection stages are the problems, which can be solved with DIESEL-RK software.  The RK-model of diesel combustion takes into account evolution of fuel sprays in a charge, wherein combustion of a pilot fuel portion has taken place already.

      In this page some results of calculation of mixture formation and combustion in medium-speed diesel with double stage injection are presented. The pilot injection fraction is about 11 % of full fuel supply. Fuel Spray Visualization shows  that burning of pilot fuel occurs after its injection. The main injection begins during afterburning of pilot fuel.  

 

1400_1.GIF (85472 bytes)

The heat release diagram gives the comparison between calculated and measured data (experimental red curve was obtained in Kolomna plant).

 

 

Diagrams of injection pressure p_inj and injection velocity v_inj.

The maximum injection pressure  is about 1200 bars.

      The picture of mixture formation shows evolution of sprays in a shallow piston bowl of the locomotive diesel.

      The spray, meeting with the piston surface at the acute angle, forms narrow and prolate in radial direction wall surface flow.  This configuration of spots allows the increase number of nozzles or use a swirl, whereas in a conventional, deep combustion chamber these cause overintersection of wall surface flows and degradation of engine characteristics.
      On the other hand, a shallow piston bowl requires precise orientation of injector nozzles to avoid hit of fuel on a cylinder liner.

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