A STUDY OF SHOСK WAVE PROCESSES IN THE COMBUSTION CHAMBER AND THE ESTIMATION METHOD OF THE KNOCK INTENSITY BASED ON ION CURRENT SIGNAL ANALYSIS Artem Yurevich Budko, Anatolij Sergeevich Nazarkin and Mikhail Yurevich Medvedev Southern Federal University, Rostov-on-Don, Russia E-Mail: sedu-budko@mail.ru ABSTRACT The article is ocused on the study o shock-wave processes in the combustion chamber on the basis o the ion current signal analysis. The possibility o detecting shock waves and estimating their intensity in the combustion chamber rom the ion current signal is theoretically substantiated and experimentally proved. A criterion o the non-knock combustion process is given. It is based on spectral power density unction analysis o the detected ion current signal. The proposed method or calculating the perturbations o the ion current signal in the shock wave processes is based on calculation o the undamental and multiple harmonics o the standing wave packet arising in the combustion chamber during knock. The calculation o harmonics or standing waves which is based on the calculation o the conditions or the existence o standing waves and it takes into account the geometric dimensions o the combustion chamber and the velocity o propagation o shock waves. The spectral power density unction o the detected ion current signal is calculated to study shock-wave processes. The obtained unction o test signal calculation is approximated by a polynomial o the second degree. To estimate the energy o the shock wave packet, the unction o the approximating polynomial is subtracted rom the spectral power density unction o the detected ion current signal. The energy o shock waves is estimated as the sum o the dierence in areas under the test and calculated unctions in the range o requencies o standing waves existence calculated or a given combustion chamber. The results o an estimate o the knock intensity o our-stroke internal combustion engine with a combustion chamber diameter o 82 mm are given as an example. Keywords: internal combustion engine, ion current, spectral analysis, knocks detection. INTRODUCTION A knock is one o the main actors limiting the power o the internal combustion engine (ICE) [1-19]. The knock is a result o sel-ignition o the uel-air mixture (hereinater, FAM). It occurs in the region in ront o the turbulent lame, leading to a rapid release o energy. An emergence o high local pressure leads to compression waves propagation within ICE. Shock waves encountered in knock combustion process, result in damage eects o ICE, deterioration o engine values and increasing o harmul substances in the exhaust gases. To date, indirect methods or detection o knock combustion are widespread. These methods are based on the act that vibrations and noise generated during knocking are excited by compression waves at certain requencies corresponding to the resonant modes o the combustion chamber [1-21]. It is known that a group o waves with dierent velocities and energy arise upon knock combustion [1-19]. The inluence o various waves and their harmonics on the processes upon knock combustion could be estimated using spectral analysis methods. Figure-1 shows the plots o its power spectral density (PSD) or knock combustion obtained by engineers rom General Motors [7, 8]. Figure-1. The PSD plots upon knocking in ICE. The knock detection is available by iltering the sensor signals o pressure, combustion, vibration, sound, ion current, accelerometers and using other band-pass ilters at the requency o the main shock wave harmonics. Narrow- and wideband knock sensors (hereinater KS) based on the piezoelectric eect, track the vibration occurring at the desired requency. The problem o this method is a strong noisy signal, caused by the vibrations o the running engine. A lot o moving parts and details o the internal combustion engine produce oscillations with a requency lying within the target range. These noises reduce the reliability o the result. The method o direct pressure measurement in the ICE cylinder gives more reliable and accurate results o knock detection, since vibrations and noises emitted by the engine parts have no signiicant eect on combustion 3667
pressure sensor. The method is highly sensitive, allows detecting knock o varying intensity, including at its initial stage. However, the use o knock signal sensors oten is limited to the stages o research, calibration and diagnosis o ICE, because o small resource and a high cost. The problem o signal noise in the target requency range, low sensitivity, low resource and high cost o devices and components o the knock combustion detection system could be solved by the method o the ion current signal (ICS) recording. Since the measurements, as in the case o the combustion pressure sensor, are carried out directly in the combustion chamber, they have high reliability, and the noise and vibration o the ICE parts do not aect the ICS. This highly sensitive method does not require the use o expensive materials, sensors and electronic components. The objective o the work is to study the eect o wave propagation in the combustion chamber on ICS and to develop estimation method o energy shock wave packet arising rom knock combustion in the ICE. The study o the eect o combustion parameters on the spectrum o the ion current signal and the development o a method or estimating the detonation intensity The experiment was carried out or normal and knock combustion. The plots o ICS and the estimated power spectral density (PSD) are shown in Figure 2. All the plots provided in this article were obtained using MATLAB. Experimental data were obtained or a combustion chamber with a diameter o 82 mm. The main resonant requency or this diameter is approximately 7000 Hz [2, 19]. (a) (b) Figure-2. ICS and PSD o (a) - normal combustion, (b) - high knock combustion. 3668
The plots o estimated power spectral density ICS or knock combustion (see Figure-1 (b)) shows dierent spikes. The requency o a standing wave depends on the speed o sound in the environment, the wavelength and the geometry o the combustion chamber [2, 19]. The assumption that the standing wave in the combustion chamber is lat allows us to calculate the requencies o the harmonics according to equations (1): = V λ = V d ; = V λ = V d = ; = V = V = λ d ; { n = V = nv = n λ n d, where are the requencies o the undamental and higher harmonics respectively, are the wavelengths o the undamental and higher harmonics, respectively, - is the wave velocity, is the cylinder diameter. Calculation o the power spectral density o the detected ion current signal produced by the algorithm computing the discrete ast Fourier transormation (DFT) by (2) when k=0, 1,, (N-1) [20]. (1) where, - conidence interval o recorded wave requency determined experimentally. The system o equations (5) or inding the coeicients o the polynomial (3) is based the calculated values o : Where - are the requencies corresponding to the calculated by expression (4) Figure-3 shows the result o calculation using (1)... (5) or 30 consecutive cycles o knock combustion in one o the ICE cylinders. (4) (5) where dimension, sequence (2) is the sampling requency, N is the DFT is the N-point DFT o the N-point - is the discrete normalized requency, - is the power spectral density. The calculation o the PSD unction o the normal combustion is perormed by approximating the envelope o the PSD unction or the recorded signal curve in sections between the requencies This technique is based on the spectrogram analysis or normal combustion o FAM (Figure-1 (a)), which shows that the envelope o the PSD unction has a smooth character without pronounced spikes on the requency bands o the waves arising rom knock combustion. Approximation o ICE PSD unction can be a polynomial o the second degree (3): (a) (3) where is the amplitude o the signal envelope; are the polynomial coeicients; is the requency. To ind the values o the unction the average amplitudes o the PSD unction are calculated at sites between the requencies in accordance with the expressions (4): (b) Figure-3. PSD unction: upon knock ( ); a calculated value o normal combustion (b). 3669
The energy o the shock waves is estimated as the dierence between the integral values o the PSD unction or recorded signal and or calculated values or normal combustion in requencies domain with (6): in accordance o the recorded signal and calculated by (3) or normal combustion. P, Д P, db/hz 30 30 25 25 P() s() 20 20 s 1 P 1 where - is the estimated energy o the shock wave harmonics. The expression or total energy o the shock waves calculation is given (7): The knock intensity is estimated by (8): (6) (7) 15 15 10 10 5 5 0 0 s1 P, db/hz 30 25 2 4-6 + 8 10 12 2 14 3 16 18, khz кгц P() 1 P s1 (a) s 2 s 3 (8) 20 s 1 s() where - are the integral values o the PSD unction or normal combustion, which are on the right-hand side o expression (6). 15 10 An example o knock intensity using proposed method Figure-4 (a) shows an example o the calculation or a shock wave in a our-stroke internal combustion engine with a cylinder diameter o 82 mm using expressions (1)... (7). For other components o the shock wave, the calculations are similar. In the graphical representation, the energy o the shock waves is equal to the dierence in the areas under the experimental and PSD unctions calculated or the target requency band. The total energy o the waves is equal to the sum o the areas calculated or all the target ranges determined by the requencies and the conidence interval. Figure-4 (b) shows examples o PSD unction plots 5 0 2 s1 - + 10 2 3 16 18, khz s 3 1 (b) Figure-4. The experimental (green line) and the calculated (blue line) PSD o the ion current signal or knock (a) and normal (b) combustion o FAM. Table-1 shows the results o the calculations made using the proposed method or the PSD unctions, presented in Figure-4. s 2 Parameter Total sum o estimated energy o shock-waves Table-1. Results. Knock combustion Normal combustion 251,035 13,511 Estimated intensity o knock 0,4857 0,0294 The results in Table-1 show high resolving power o the proposed method, since the shock wave energy calculated or normal and detonation combustion dier by an order o magnitude. For 330 successive cycles o knock combustion, the degree o reliability o detection o detonation by the proposed method turned out to be 8% higher than the methods based on bandpass iltration o ICS. 3670
CONCLUSIONS The paper presents the results o an experimental study o the ion current signal under various combustion conditions. As a result o the analysis o the spectra o recorded ICS or various combustion modes o FAM the ollowing conclusions have been drawn: the requencies at which resonance phenomena occur could be calculated using equations o plane wave; under normal combustion, the ICS spectrum has a smooth character without pronounced spikes, including in the requency range with resonant phenomena; in knock it has been observed increasing amplitude o the waves in the requency range with resonance phenomena, as shown by spikes on the spectrogram; the nature o the spectrum is common and uniied or dierent combustion modes o FAM or the single combustion cycle signal and statistical ICS samples. The developed method or estimating the detonation intensity in ICS is based on the calculated requencies o the harmonics o shock waves. It allows taking into account the energies o waves or dierent velocities and requencies. An estimation o the energy o detonation waves occurs over the area o the PSD unction in the region o the calculated requencies o standing waves. The paper presents calculation results o knock wave energy using proposed method or normal and knock combustion in a our-stroke ICE with a cylinder diameter o 82 mm, the results show high resolving power o the proposed method, since the shock wave energy calculated or normal and detonation combustion dier by an order o magnitude. ACKNOWLEDGEMENTS This work was partially inancially supported by Russian Foundation or Basic Research (RFBR) (Project 16-38-00025 "New methods o the analysis o ion currents as a tool or research and optimize o the internal combustion engine"). REFERENCES [1] Heywood J.B. 1988. Internal Combustion Engine Fundamentals. McGraw Hill Inc., New York. [2] Lee J., Hwang S., Lim J., et al. A New Knock- Detection Method using Cylinder Pressure, Block Vibration and Sound Pressure Signals rom a SI Engine. SAE 981436. [3] Kaneyasu М. et al. Engine Knock Detection Using Multi-Spectrum Method. SAE 920702. [4] Chiriac R., Radu B. and Apostolescu N. Deining Knock Characteristics and Autoignition Conditions o LPG with a Possible Correlation or the Control Strategy in a SI Engine. SAE 2006-01-0227. [5] Budko A. Yu., Medvedev M. Yu., Budko R. Yu., Ivashin P. V., Tverdokhlebov A. Ya., Gerasimov D. N., Rakhmanov V. V. 2017. Control o the Combustion Process Parameters in ICE by the Ion Current Signals, Mekhatronika, Avtomatizatsiya, Upravlenie. 18(4): 256-263. DOI: 10.17587/mau.18.256-263. [6] Artem Yu. Budko, Michail Yu. Medvedev, Raisa Yu. Budko, Pavel V. Ivashin, Andrey Ya. Tverdokhlebov, Dmitriy N. Gerasimov, and Vitaly V. Rakhmanov. 2017. Analysis o Ion Current Integral Characteristics or Estimation o Combustion Process Parameters in Internal Combustion Engines. International Journal o Mechanical Engineering and Robotics Research. 6(3): 188-193. DOI: 10.18178/ijmerr.6.3.188-193. [7] Patent US 7181339 B2 George Mark Remelman, Real-time spectral analysis o internal combustion engine knock // Bibliographic data: 2007-02-20. [8] General Motors Orders KRONOS-V - The Industry s First Real-time Knock Analysis System// Electronic resource: http://www.vxiproducts.com/news.htm (26.07.2014) [9] Lee J., Hwang S., Lim J., et al. A New Knock- Detection Method using Cylinder Pressure, Block Vibration and Sound Pressure Signals rom a SI Engine. SAE 981436. [10] Kaneyasu М, et al. 1999. Engine Knock Detection Using Multi-Spectrum Method. SAE 920702, pp. 136-145. [11] Chiriac R., Radu B. and Apostolescu N. 2000. Deining Knock Characteristics and Autoignition Conditions o LPG with a Possible Correlation or the Control Strategy in a SI Engine. SAE 2006-01-0227, pp. 466-498. [12] Grandin B., Denbratt I., et al. 2000. Heat Release in the End-Gas Prior to Knock in Lean, Rich and Stoichiometric Mixtures With and Without EGR. SAE 2002-01-0239, pp. 244-256. [13] Bradley D., Morley C., et al. 2005. Ampliied Pressure Waves During Autoignition: Relevance to CAI Engines. SAE 2002-01-2868, pp. 76-89. [14] Konig G. and Sheppard, C.G.W. 2004. End Gas Autoignition and Knock in a Spark Ignition Engine. SAE 902135, pp. 176-191. 3671
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