Abstract
The origin of light emission during low-temperature combustion in a light-duty IC engine is investigated by high-speed spectroscopy in both HCCI and PPC regimes. Chemiluminescence and thermal radiation are expected to be the dominant sources of light emission during combustion. A method has been developed to distinguish chemiluminescence from thermal radiation, and different chemiluminescing species could be identified. Different combustion modes and global equivalence ratios are analyzed in this manner. The results indicate that the spectral signature (270–540 nm range) of the combustion is highly dependent on the stratification level. A significant broadband chemiluminescence signal is detected and superimposed on all spectra. This broadband chemiluminescence signal can reach up to 100 percent of the total signal in HCCI combustion, while it drops to around 80 percent for stratified combustion (PPC). We show that this broadband signal can be used as a measure for the heat release rate. The broadband chemiluminescence did also correlate with the equivalence ratio quite well in both HCCI and PPC regimes, suggesting that the total emission in the spectral region of 330–400 nm can serve as a proxy of equivalence ratio and the rate of heat release. Regarding C2* chemiluminescence, we see two different chemical mechanisms for formation of C2* in the PPC regime: first during the early stage of combustion by the breakup of bigger molecules and the second during the late stage of combustion when soot particles are forming.
Highlights
Premixed combustion (PPC), a combustion mode of compression-ignition (CI) internal combustion (IC)1 3 Vol.:(0123456789)108 Page 2 of 13 engines, relies on a relatively long ignition delay (ID) to achieve a partially premixed charge [1,2,3,4,5,6]
Thermal radiation is mainly composed of black-body radiation coming from soot particles that are heated to flame temperatures by the combustion process [8], while the term chemiluminescence is used for the light emission of specific molecules, which are formed in an electronically excited state during combustion and spontaneously decay back to lower energy levels [8, 9]
The objective of this study was to evaluate the spectral signature of partially premixed combustion at different stratification levels
Summary
Premixed combustion (PPC), a combustion mode of compression-ignition (CI) internal combustion (IC)1 3 Vol.:(0123456789)108 Page 2 of 13 engines, relies on a relatively long ignition delay (ID) to achieve a partially premixed charge [1,2,3,4,5,6]. PPC is a promising combustion concept allowing to reduce both NOx and soot emissions while providing high combustion efficiency. By coupling a high-speed camera to a spectrograph, crank-angle- and cycle-resolved spectroscopic data, containing detailed information regarding the species formation during the combustion, can be obtained. Thermal radiation is mainly composed of black-body radiation coming from soot particles that are heated to flame temperatures by the combustion process [8], while the term chemiluminescence is used for the light emission of specific molecules, which are formed in an electronically excited state during combustion and spontaneously decay back to lower energy levels [8, 9]. The chemiluminescence yield due to specific molecules varies for different combustion regimes, and this can provide information about the nature of the chemistry involved [9,10,11]. Chemiluminescence imaging is a useful tool for time- and space-resolved investigation of the reactions that occur during combustion [13]
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