Sánchez, F., Braga, C., Braga, L., Braga, S. et al., "Experimental Study of the Ignition Delay for Ethanol-Powered in a Rapid Compression Machine," SAE Technical Paper 2014-36-0127, 2014, doi:10.4271/2014-36-0127.
The period between the start of fuel injection into the combustion chamber and the start of combustion it's known as Ignition Delay (ID) or Delay Time. Delay period in the diesel engine exerts a very great influence on both engine design and performance. Functionally, the ID can be divided into two parts: the physical and chemical delay. The physical delay, it is the time between the beginning of injection and the attainment of chemical reaction conditions. During this period, the fuel is atomized, vaporized, mixed with air and raised to self-ignition temperature. Viscosity governs the physical delay of fuel combustion process, for low viscosity fuels, the physical delay tends to be small and vice versa. The chemical delay, during this period reactions start slowly and the accelerate until inflammation or ignitions takes place. Generally, chemical delay is larger than the physical delay. However, it depends on the temperatures thus physical delay becomes longer than the chemical delay. The methods to determine the ignition delay can be broadly classified into two categories: The direct and the indirect methods. Once the rapid compression machine (RCM) already has a piston with a quartz visibility window, the method adopted in the present work was based on the direct method. All tests performed in the RCM had their combustions filmed using a high speed camera. A post-processing of these images enabled us to determine with good precision in which frame the combustion was initiated. Knowing the frame that the combustion starts, the frame rate used during the films and the exact moment when the fuel was injected was possible to evaluate the ignition delay.