A combustion-led engine design approach for achieving ultra-low engine emissions for future automotive applications

  • Faizan Khalid

Student thesis: Doctoral Thesis

Abstract

Future of automotive industry relies heavily on the engine combustion systems that
are free from hazardous environmental emissions. Low temperature combustion
strategies result in the reduction of NOx, UHC, CO and soot formations by use of lean
fuel-air mixtures. ‘Reaction kinetics’ plays an important role in controlling the engine
combustion at lower temperatures. Mixture temperature (T), pressure (P) and
composition (φ) are the three key parameters that play an important part in controlling
the rate of reaction and thus production of the engine emissions.

In this work, 0-D, constant-volume CHEMKIN reaction-kinetics modelling was applied
to methane (CH4), iso-octane (C8H18) and n-dodecane (C12H26) hydrocarbons.
Using a combustion-focused approach, suitable thermodynamic conditions (i.e., T, P
and φ) were defined at start so that complete combustion of the reaction mixture
doesn’t produce any emissions. An operational window for the higher and lower
temperature limits was identified. It was found that C12H26 and C8H18 gave much
lower ignition temperatures starting at 690K and 910K respectively at lean equivalence
ratios in comparison with 1520K for CH4 hydrocarbon. Extending the 0-D, constant
volume modelling results to 3-D FORTE’ variable-volume engine cylinder geometry
using ‘n-dodecane’ as the representative fuel showed that ultra-low NOx emissions of
0.085 g/kw-h (for a heavy duty Euro 6 NOx limit of 0.4g/kW-h) can be achieved with a
model start temperature of 689K. A late combustion in the expansion stroke resulted
in lower peak combustion temperatures and slightly lower than the maximum indicated
power produced. Soot, CO and UHC emissions were also negligible in this case as
the fuel-air mixture was lean. Finally, 3-D FORTE’ engine simulations were applied to
the ‘combustor’ cylinder of a recuperated split cycle engine (RSCE) to evaluate the
combustion and emissions performance at 1200 engine rpm representing typical
motorway cruise conditions for a heavy duty commercial vehicle. Out of all the four
simulation cases run, ‘Simulation 4’ with the retarded IVC and SOI timings gave the
most optimum results with the highest indicated power exceeding the experimental
value by 3% and 32% lower NOx emissions than the experiment. Based on the engine
model simulation results, it was also found out that the UHC emissions and lower
exhaust gas temperatures could be potential problems for the RSCE combustion.
Date of AwardOct 2019
Original languageEnglish
Awarding Institution
  • University of Brighton
SponsorsRicardo
SupervisorRobert Morgan (Supervisor), David Mason (Supervisor), Morgan Heikal (Supervisor) & Andrew Atkins (Supervisor)

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