Investigation of a ‘SCR free’ system (LP EGR, twostage boosting system and 3000 bar High Pressure Common Rail System) to meet the Stage IV and beyond emissions limits
Heavy-Duty-, On- und Off-Highway-Motoren 2016
11. Internationale MTZ-Fachtagung
Referent(in): Paolo Gatti, Simon Fagg, Federico Millo, Giulio Boccardo, Stefano Manelli, Andrea Marinoni
In the emission range above 55kW Kohler Engines have developed the KDI 3.4 litre engine
to meet the Stage IV exhaust emissions limits using the Ricardo TVCS low soot combustion
system plus DOC and SCR aftertreatment system.
For the current Stage IV strategy, the 3.4 litre engine uses moderate EGR rates and requires
a reduction in NOx emissions of around 90% over the SCR system.
A potential option alternative to the SCR to meet the Stage IV and beyond emission
standards with a reduced complexity in engine and aftertreatment hardware layout and
system management have been investigated.
For emission standards beyond Stage IV there will be no change in the NOx emissions limit,
but PM will be reduced from 0.025 g/kWh to 0.010 g/kWh and a Particle Number limit will be
added to force engine manufacturers to fit DPFs, even on low soot engines.
A typical exhaust aftertreatment package for Stage V includes DOC, DPF and SCR, then
this appears to be a costly and bulky solution in case of industrial, construction equipment
and agricultural applications with severe packaging requirements, hence an alternative
solution would be to increase EGR rates further to reduce NOx and hence eliminate the
requirement for SCR aftertreatment.
High rates of EGR place additional requirements on the boosting system hence a two stage
system have been specified.
Higher fuel injection pressures (up to 3000 bar) can compensate for the dilution of the airfuel
mixture, enabling low soot to be attained at high EGR rates.
A combustion system hardware (combustion chamber shape, inlet swirl requirement, nozzle
library, nozzle protrusion, etc) have been optimised for the 3000 bar FIE system through 1-D
cycle simulations and 3-D CFD analysis to investigate the interactions between nozzle hole
diameter, number of nozzle holes, target injection period and piston bowl diameter to obtain
the best nozzle/chamber match.
Hardware screening has been performed on test bench to define the best nozzle match on
the basis of NOx-PM-BSFC trade-offs at selected key-points, varying some parameters
including injection timing, rail pressure and EGR rate, fuelling quantities and injection
strategy (post injection).
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