The Influence of Fuel Volatility on the Liquid-Phase Fuel Penetration in a Heavy-Duty D.I. Diesel Engine

The objective of this investigation is to verify and characterize the influence of fuel volatility on maximum liquid-phase fuel penetration for a variety of actual Diesel fuels under realistic Diesel engine operating conditions. To do so, liquid-phase fuel penetration was measured for a total of eight Diesel fuels using laser elastic-scatter imaging. The experiments were carried out in an optically accessible Diesel engine of the “heavy-duty” size class at a representative medium speed (1200 rpm) operating condition. In addition to liquid-phase fuel penetration, ignition delay was assessed for each fuel based on pressure-derived apparent heat release rate and needle lift data.

For all fuels examined, it was observed that initially the liquid fuel penetrates almost linearly with increasing crank angle until reaching a maximum characteristic length. Beyond this characteristic length, the fuel is entirely vapor phase and not just smaller fuel droplets. The analysis also shows that there is a strong, essentially linear correlation between fuel mid-boiling point and maximum liquid-jet penetration. For example, for an increase in the fuel mid-boiling point from 220°C to 340°C, there was a corresponding increase in measured maximum liquid length from 21 to 35 mm for the operating condition investigated. However, no general correlation between mid-boiling point and measured ignition delay was evident, which indicates that chemical processes dominate physical ones with regard to autoignition. The data additionally indicate that in this type of Diesel engine (under typical warm-engine conditions), maximum liquid-fuel penetration occurs well before wall impingement, even for relatively high boiling point fuels.