If this influencing process is carried out in accordance with a predetermined, selected time function, the combustion flame and thus the instantaneous rate at which heat is released can be modulated appropriately. Since the instantaneous rate at which heat is produced represents the most important single factor in the production and suppression of thermoacoustic combustion instabilities, the instabilities can effectively be suppressed by suitable selection of the time function and other modulation variables.
According to one preferred embodiment of the method according to the invention, a high voltage of several kV is used for modulation and is, in particular, a pulsating DC voltage, with a periodic function being used as the time function. In this case, the high voltage can on the one hand be modulated in an open control loop. This is justified in particular if the instabilities in the combustion chamber have a response which is constant over time and can be suppressed or attenuated by selection of a suitable fixed time function.
If, on the other hand, the instabilities vary with time or as a function of various changing operating parameters, it is expedient and advantageous to monitor the hydrodynamic instabilities continuously by measuring suitable variables, in particular the instantaneous rate at which heat is released or the pressure pulsations, and to carry out the modulation process in a closed control loop, including the measured variables. The combustion system according to the invention, which comprises a combustion chamber and at least one injection nozzle through which liquid fuel is injected into the combustion chamber, is distinguished in that first means are provided in order to apply an electrical voltage to the liquid fuel during the injection process.
One preferred embodiment of the combustion system according to the invention is distinguished in that the injection nozzle comprises a nozzle bore and a fuel channel which leads to the nozzle bore, in that the fuel in the fuel channel has the modulating electrical voltage applied to it, in that the injection nozzle comprises a nozzle body in which the nozzle bore is arranged, in that the fuel channel is formed between the nozzle body and an insert which is inserted with a gap into a recess in the nozzle body and is electrically insulated from the nozzle body, and in that the modulating electrical voltage is applied between the nozzle body and the insert.
The invention will be explained in more detail in the following text with reference to exemplary embodiments and in conjunction with the drawing, in which:. The combustion system 10 comprises a combustion chamber 11 in whose interior 12 an injection nozzle 13 for injection of a fuel spray 16 of liquid fuel is arranged. The liquid fuel for example oil is supplied to the injection nozzle 13 from the exterior via a fuel line The necessary combustion air enters the combustion chamber through an air inlet The fuel nozzle 13 is connected via supply lines to a controlled voltage source 17 , which emits a pulsed or clocked DC voltage in the high-voltage range of several kV, for example 10 to 20 kV.
The clock frequency is governed predominantly by the thermoacoustic combustion instabilities which can occur in the combustion chamber 11 , and is selected such that these instabilities are suppressed or are at least highly attenuated. The frequencies may in this case be in the range from several Hz to several kHz. The controlled voltage source 17 may on the one hand be permanently set to the optimum clock frequency or time function.
The control loop for suppressing the instabilities is then an open control loop. The voltage source 17 may, however, also—as is shown in FIG.
Combustion of Liquid Fuel Sprays - 1st Edition
In this case, the control process is carried out in a closed control loop. However, the instantaneous rate at which heat is released may also be measured, for example by measuring the OH radiation intensity, and used for control purposes, instead of the pressure pulsations when using the pressure transducer The pulsed high voltage from the voltage source 17 modulates the fuel spray 16 in the injection nozzle 13 indicated in FIG.
The application of electrostatic voltages to the liquid droplets allows various parameters relating to the fuel spray 16 to be influenced, such as. For their part, these parameters influence—by varying the ignition delay times, the local equivalence relationships, etc. If the high voltage on the injection nozzle is varied by the pulsation , this allows the instantaneous rate at which heat is produced in the combustion chamber 11 to be modulated, this being the most important single factor for the production, and thus for the active suppression as well, of the thermoacoustic combustion instabilities.
The high voltage can be applied to the injected fuel in an injection nozzle 13 , a longitudinal section of which is shown in FIG. The injection nozzle 13 comprises a nozzle bore 23 and a fuel channel 22 which leads to the nozzle bore The modulating electrical voltage is applied to the fuel in the fuel channel To this end, the injection nozzle 13 comprises a nozzle body 20 in which the nozzle bore 23 is arranged.
Subscribe Search My Account Login. Rent or Buy article Get time limited or full article access on ReadCube. References 1 Lloyd, Proc. Google Scholar 3 Stefan, Wien Ber. Google Scholar 4 Sresnewski, J. Google Scholar 5 Morse, Proc.
Combustion of Droplets in a Fuel Spray
Article Google Scholar 6 Fuchs, Phys. Google Scholar 8 Wolfhard and Parker, J. Rights and permissions Reprints and Permissions. Thomas Avedisian Combustion and Flame Fundamentals of oil combustion Alan Williams Progress in Energy and Combustion Science Combustion of droplets of liquid fuels: A review Alan Williams Combustion and Flame An experimental study on the combustion of a fuel droplet Kiyosi Kobayasi Symposium International on Combustion Studies of the combustion of drops in a fuel spray—the burning of single drops of fuel G.
Godsave Symposium International on Combustion Comments By submitting a comment you agree to abide by our Terms and Community Guidelines. Nature menu.
Nature Research menu. The data collection system consisted of a high repetition rate diode pumped Nd:YAG laser frequency doubled to nm for visible illumination and a Kodak High Speed Motion Analyzer for recording fuel spray images. The engine was motored under various inlet conditions to create an engine combustion chamber environment typical of those found in commercial engines of similar per cylinder displacement class.
Parameters studied as independent variables that could affect fuel injection characteristics were; combustion chamber density and combustion chamber temperature at top dead center, engine speed measured in revolutions per minute, fuel injection pressure and fuel injection duration. Liquid fuel spray characteristics measured were; maximum linear penetration distance, maximum spray spreading angle and average penetration velocity.
Modelling of Nitric Oxide Formation During Liquid Fuel Combustion
Coupled with penetration distance is also the occurrence of spray to wall impingement. Spray penetration distance, spreading angle and velocity are important in the effort to gain greater understanding of spray behavior in the engine combustion chamber environment.
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Spray to wall impingement is of interest due to its perceived role in increased emission of soot and unburned hydrocarbons.