Optical diagnostics of low-temperature ignition and combustion characteristics of diesel/kerosene blends under cold-start conditions

Diesel engine plays a vital role in various fields, but it does suffer from the cold-start issue when operating in low-temperature environment. As an alternative fuel or emergency back-up fuel for diesel engine, kerosene was investigated to reveal the influences of its difference on physical and chemical properties from diesel on low-temperature ignition characteristics. In this work, the spray and ignition characteristics of diesel/kerosene blends were investigated at ambient temperatures of 653–733 K and ambient densities of 10–22 kg/m³. Experiments were conducted in an optical constant volume combustion chamber using Mie-scattering and direct photography methods. The results show that under cold-start conditions, although kerosene has lower cetane number than diesel, its strong volatility significantly promotes the atomization and evaporation of the blends. The addition of 15% volumetric kerosene to diesel effectively shortens the ignition delay. In addition, the low-temperature ignition starts with a blue flame and further formaldehyde signal identification indicates that the blue flame is a cool flame. Kerosene addition enhances the cool flame intensity, which is conducive to the transformation to a high-temperature hot flame. Thus, adding a small proportion of kerosene to the diesel fuel contributes to a rapid cold-start at low temperatures.