THE EFFECT OF DILUENT ON THE SUSTAINABILITY OF MILD COMBUSTION IN A CYCLONIC BURNER

The present study investigates the characteristics of MILD/Flameless Combustion in a prismatic (20x20x5 cm3) laboratory-scale burner. The main pre-heated flow rate composed by diluent and oxygen and the fuel (at environmental temperature) are fed inside the combustion chamber from one side. Diametrically opposed the feeding configuration is reproduced, thus realizing a cyclonic flow field inside the reactor. The outlet is located on the top of the chamber. The combustor was designed to operate at a nominal heat load of 2 kW. In the non-premixed mode the oxidizer is supplied with a jet adjacent to the fuel injector. Fuel jets are adjacent to the combustor wall and oxidizer is injected between the fuel jet and centerline of the combustor. The gases are expected to recirculate downwards along the combustor centerline. The chamber is made of vermiculite. The system is provided with a quartz window and some thermocouples to measure the temperature profiles inside the burner. The oxidation process of C3H8/O2 mixtures diluted in N2 and CO2 was studied varying external parameters of the system, namely inlet temperatures (up to 1200K) and equivalence ratio (lean to reach mixtures) to identify the combustion regimes in a non-premixed facility. In particular the effect of diluent nature on the establishment of Flameless conditions inside the chamber was investigated. The initial stabilization temperature is a bit higher if the mixture is diluted in CO2. Increasing the preheating temperature, MILD occurs and combustion becomes invisible and homogeneous. A numerical simulation of the chamber was performed using perfectly stirred flow reactor to simulate MILD combustion and to compare it with the experimental results.