Investigation of fuel volatility on the heat transfer dynamics on piston surface due to the pulsed spray impingement

Abstract

The fuel spray in a gasoline direct injection (GDI) engine can impinge on the piston surface to form a liquid film, which leads to a decrease of the combustion efficiency and the increase of particulate emissions. The dynamic heat transfer process resulting from the impingement has an important effect on the evaporation of the liquid film and its residence time. In this study, two pure component fuels (methanol and n-pentane), and three fuel blends with different initial boiling points and enthalpies of vaporization marked as Fuel B, Fuel C and Fuel D, are designed to investigate the effect of the fuel volatility on heat transfer dynamics of pulsed spray impingement with different: injection temperatures (Tinj), injection pressures (Pinj), piston temperatures (Tpis) and injection distances (Dinj). The results show that the spray a transient heat transfer induced by different fuel sprays are very sensitive to changes of Tinj and Dinj, and also depend on their boiling points and enthalpies of vaporization. The impinging and cooling intensities are greatly reduced when the pressure ratio of ambient pressure to saturation pressure (Pa/Psat) decreases, as a result of increasing Tinj. The maximum surface temperature drop (ΔTs, max) and peak heat flux (qmax) on the impinging surface are reduced greatly by over 60% for fuels with low enthalpy of vaporization such as n-pentane, Fuel B, Fuel C and Fuel D, while they are only reduced by less than 15% for methanol with highest enthalpy of vaporization when Tinj increases from 25°C to 140°C. Exponential equations are proposed to describe the relationship between qmax and Pa/Psat. When Dinj increases from 50 mm to 70 mm, qmax is reduced by over 10% for fuels such as n-pentane, methanol, Fuel B and Fuel C with low initial boiling points, whereas qmax is increased slightly by 7% for Fuel D with the highest boiling point. On the other hand, the transient heat transfer of different fuels present similar trends in response to the changes of Pinj and Tpis. ΔTs, max and qmax nearly present a linear variation with Pinj and Tpis for all fuels.