Outline

  • Abstract
  • Keywords
  • 1. Introduction
  • 2. Experimental Procedure and Fuels
  • 3. Results and Discussion
  • 3.1. Effect of Alcohol Content
  • 3.2. Effect of Initial Temperature
  • 3.3. Effect of Initial Pressure
  • 4. Conclusions
  • Acknowledgements
  • Nomenclature
  • References

رئوس مطالب

  • چکیده
  • 1. مقدمه
  • 2. روش تجربی و سوخت
  • 3. نتایج و بحث
  • 3.1. تأثیر محتوای الکل
  • 3.2. تأثیر دمای اولیه
  • 3.3. تأثیر فشار اولیه
  • 4. نتیجه گیری

Abstract

Recently, there is increasing interest in using butanol as a renewable component not only for gasoline but also for diesel fuels. This work investigates the effect of its concentration on diesel and biodiesel blends on the autoignition time, comparatively to equivalent blends with ethanol, in a constant-volume combustion chamber. The increase of alcohol content in diesel or biodiesel, led to an increase in autoignition times. Such increase was not linear but sharper for high alcohol contents, and was higher with ethanol than with butanol. For butanol blends, the increase in delay time was very similar when diesel or biodiesel were used. The maximum pressure during combustion decreases as the alcohol content was increased, especially in the case of ethanol, as a consequence of energy, chemical and dilution effects. However, for low ethanol or butanol concentrations, some increases in the pressure peaks were observed by a combination of compensating effects: increase in the amount of premixed combustion and increase in the flame speed. For 10% v/v alcohol blends in diesel or biodiesel, the delay times decreased as both the initial pressure and the initial temperature were increased, the latter effect being slightly higher with biodiesel compared to diesel.

Keywords: - - - - -

Conclusions

The following conclusions can be drawn from the present study:

  • The increase in alcohol content in diesel or biodiesel fuels always led to an increase in both IDCF and IDM. Such an increase was sharper at high alcohol contents. This implies that weight or volume averaging of autoignition parameters (such as cetane number) is not an accurate method to predict the autoignition behaviour of alcohol blends.
  • The increase in the delay time with the ethanol content is more prominent than for butanol, consistently with its lower cetane number. However, the differences in autoignition time become more visible when these alcohols are blended with diesel fuel whereas they become less significant when they are blended with biodiesel fuel (at least for high alcohol contents).
  • For butanol blends, the increase in autoignition delay time is very similar when diesel or biodiesel (with similar cetane numbers) were used in the blends. However, some differences appear when ethanol is blended with diesel or biodiesel fuels, with larger delay times in the former case.
  • The maximum pressure in the combustion chamber was observed to decrease as the alcohol content was increased, especially in the case of ethanol, as a consequence of the reduced heating value, of the reduced equivalence ratio and of the over-dilution caused by their large delay times.
  • Some increases in the pressure peaks were observed in a narrow range of low ethanol and butanol contents (especially in butanol blends), probably due to a combination of effects which compensate the above mentioned effects: increase in the amount of premixed combustion and increase in the flame speed derived from the presence of alcohols in the blends.
  • For blends with 10% v/v alcohol and 90% diesel (or biodiesel), the autoignition delay times decrease as the temperature increases. This effect is slightly more prominent for biodiesel than for diesel fuel, as a consequence of the physical properties of biodiesel (mainly higher viscosity and higher boiling point) which lead to some contribution of the physical delay especially at moderate temperatures.
  • For blends with 10% v/v alcohol, the autoignition delay times increase exponentially as the pressure is decreased (for equal equivalence ratio). The fitting exponents are similar for both alcohols, but higher for diesel blends than for biodiesel ones. However, such increase is partly compensated by the increase in equivalence ratio.
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