Since it is one component, in numerical simulations n-heptane is generally chosen to represent diesel fuel. In the constant volume experiments of this study, n-heptane is also tested to observe its ignition delay properties. Ignition delay and ignition characteristics of n-heptane are very similar to the ones that of diesel fuel. After autoignition, it is observed that the flame of n-heptane spreads faster than the other tested fuels, which is a result of its higher volatility. This fuel is specially tested to use its data in future numerical works. As a conclusion, it can be said that n-heptane is a good representative of diesel fuel for its self-ignition properties.

Figure 5.3.5: Image set from different injection sequences of diesel fuel for Nozzle C

Ignition experiments showed that autoignition starts at the downstream regions of the spray similar to the Dec’s conceptual model. Recent advances in injection systems bring higher injection pressures. As a result of this, fuel injected with higher injection velocities. Thus, spray carries the fuel-vapor and combustible air-fuel mixture through to the downstream regions where remainder fuel rapidly vaporizes with the entrained hot-air. Observed ignition locations are all at the downstream section of the spray and generally ignition starts at multiple points.