Impact of Cetane number and aromatic content on diesel ignition delay under different EGR dilution levels

Paper #:
  • 2018-01-0231

  • 2018-04-03
Ignition delay plays a vital role in diesel engines for engine efficiency and combustion noise. In order to mitigate pollutant emissions, recent research utilizes advanced combustion strategies, such as the low temperature combustion and reactivity controlled compression ignition, where critical air-fuel mixing and chemical reaction occur during the prolonged ignition delay period. Exhaust gas recirculation (EGR) is generally used to dilute the engine intake charge in these advanced combustion strategies to facilitate the modulation of the cylinder charge reactivity and thus achieve the desirable ignition delay time. In addition, changes of fuels or fuel properties can impact the ignition delay substantially. This empirical work investigates the impact of fuel Cetane number and aromatic content on diesel ignition delay time. The test fuels offer a range of Cetane numbers from 28 to 54 and aromatic content from 20% to 45%. Systematic tests are conducted on a single-cylinder research engine to evaluate the ignition delay changes due to the fuel property differences at low, medium and high engine loads under different EGR dilution ratios. The experimental results of ignition delay are used to correlate an ignition delay model modified from Arrhenius’ expression. As suggested by the data, at a lower EGR dilution level, the diesel combustion exhibits characteristics of high temperature combustion with short ignition delay and the differences in fuel properties make minor differences in combustion heat release. As EGR dilution increases and flame temperature reduces, the fuel properties start to show noticeable impacts on the reactions during the prolonged ignition delay period and ultimately on the fuel-air mixing and smoke emissions. In addition, the impacts of Cetane number and aromatic content on unburned emissions and combustion stability are also investigated in this study.
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