• Energy Research

Abstract Real-time combustion and emission control is an ongoing challenge in combustion technology and science. Hence, the scope of the present paper is the investigation of the relationship between the chemiluminescent signal and the CO and NOX emissions. Flame emission spectrometry measurements were carried out to determine the characteristic free radicals of the spectra. For the experiments, a lean premixed liquid fuel burner equipped with an airblast atomizer was used in a test rig at 15 kW combustion power. The following measurement parameters were modified: combustion air flow rate, atomizing pressure, and the vertical alignment of the spectrometer. Furthermore, various half-cone angle quarls were mounted on the burner lip to extend the lean flame blowout stability limit. The CO and NOX emissions and the chemiluminescence intensity ratios of the strongest peaks of OH*, CH*, C2*, HCO*, and CH2O* were evaluated separately at first. Then a correlation analysis of the intensity ratios and the pollutant emission components was carried out. A notable linear correlation was found between both the HCO*/C2* and OH*/C2* intensity ratios and the CO emission in certain parameter combinations.

Abstract Mixture Temperature-Controlled combustion is a novel concept featuring ultra-low pollutant emission. Since the resulting distributed combustion is highly homogeneous, NOX emission can be kept below 10 ppm. The available renewable fuels worldwide vary a lot in their characteristics. Three renewable hydrocarbon fuels: coconut oil, palm oil, and waste cooking oil-rapeseed oil methyl esters were tested along with three conventional fuels: standard jet fuel (JP-8), standard diesel oil, and natural gas. The ultimate goal of the present study was the comparison of the flame structures, chemiluminescent, and pollutant emissions of various fuels, exploiting distributed combustion offered by the novel burner concept. As mixture preparation is highly sensitive to fuel vaporization, distillation curves of the five investigated liquid fuels were measured and evaluated. Density, surface tension, and viscosity were also measured to compare the estimated atomization characteristics. The tests were uniformly performed at 13.3 kW thermal power and an equivalence ratio of 0.8, varying atomizing pressure and air preheating temperature. It was found that jet fuel, diesel fuel, and coconut biodiesel bear the highest potential for distributed combustion in gas turbines, while incorrect burner setup may lead to unacceptably high emissions.

Abstract Liquid fuels are likely to remain the main energy source in long-range transportation and aviation for several decades. To reduce our dependence on fossil fuels, liquid biofuels can be blended to fossil fuels – or used purely. In this paper, coconut methyl ester, standard diesel fuel (EN590:2017), and their blends were investigated in 25 V/V% steps. A novel turbulent combustion chamber was developed to facilitate combustion in a large volume that leads to ultra-low emissions. The combustion power of the swirl burner was 13.3 kW, and the air-to-fuel equivalence ratio was 1.25. Two parameters, combustion air preheating temperature and atomizing air pressure were adjusted in the range of 150–350 °C and 0.3–0.9 bar, respectively. Both straight and lifted flames were observed. The closed, atmospheric combustion chamber resulted in CO emission below 10 ppm in the majority of the cases. NO emission varied between 60 and 183 ppm at straight flame cases and decreased below 20 ppm when the flame was lifted since the combustion occurred in a large volume. This operation mode fulfills the 2015/2193/EU directive for gas combustion by 25%, which is twice as strict as liquid fuel combustion regulations. The 90% NO emission reduction was also concluded when compared to a lean premixed prevaporized burner under similar conditions. This favorable operation mode was named as Mixture Temperature-Controlled (MTC) Combustion. The chemiluminescent emission of lifted flames was also low, however, the OH* emission of straight flames was clearly observable and followed the trends of NO emission. The MTC mode may lead to significantly decreased pollutant emission of steady-operating devices like boilers, furnaces, and both aviation and industrial gas turbines, meaning an outstanding contribution to more environmentally friendly technologies.