From 15386f5ff64705e2b5a2710fde66d80be462370b Mon Sep 17 00:00:00 2001 From: "Robin P. Clark" Date: Thu, 7 May 2026 14:48:53 +0100 Subject: [PATCH] proposal documents --- papers/proposals/chemilumesence_proposal.tex | 221 +++++++++++++++++++ papers/proposals/syngas_chemilumesence.tex | 164 ++++++++++++++ 2 files changed, 385 insertions(+) create mode 100644 papers/proposals/chemilumesence_proposal.tex create mode 100644 papers/proposals/syngas_chemilumesence.tex diff --git a/papers/proposals/chemilumesence_proposal.tex b/papers/proposals/chemilumesence_proposal.tex new file mode 100644 index 0000000..a865f8c --- /dev/null +++ b/papers/proposals/chemilumesence_proposal.tex @@ -0,0 +1,221 @@ +\documentclass[10pt,a4paper]{article} +\usepackage[margin=18mm]{geometry} +\usepackage{amsmath} +\usepackage{siunitx} +\usepackage{chemfig} +\usepackage{mhchem} + +% -------- Conditional switches -------- +\newif\ifresearch +\researchtrue % set to \researchfalse to hide research section + +\title{\vspace{-1.0cm}Optical Combustion Diagnostics Using UV/Visible Chemiluminescence} +\author{} +\date{} + +\begin{document} +\maketitle +\vspace{-0.8cm} + +\section*{Purpose} + +This note proposes a low-cost optical route for combustion diagnostics using flame +chemiluminescence. The approach is not intended to replace existing oxygen or CO +measurement systems. Instead, it provides an additional diagnostic layer for flame +quality, instability, and air/fuel condition. + +Initial tests have already shown that a transimpedance amplifier (TIA) front-end, +connected to UV-sensitive photodiodes, produces clear measurable signals from flames. +This supports the feasibility of extending the existing IR flame-detection PCB concept +towards UV and chemiluminescence sensing. + +\section*{Relevant flame chemistry} + +Hydrocarbon flames produce excited radical species during combustion. Two particularly +useful emitters are hydroxyl and methylidyne radicals: + +\[ +\ce{OH^{*} -> OH + h\nu} +\] + +\[ +\ce{CH^{*} -> CH + h\nu} +\] + +The dominant useful bands are approximately: + +\[ +\ce{OH^{*}} \approx \SI{310}{nm} +\] + +\[ +\ce{CH^{*}} \approx \SI{430}{nm} +\] + +The relative intensity of these bands is linked to combustion state. In particular, +the ratio + +\[ +R = \frac{I_{\ce{OH^{*}}}}{I_{\ce{CH^{*}}}} +\] + +may provide an indication of rich/lean tendency, while time variation in the +UV signal may provide information about flame instability, lift-off, pulsation, +or incipient poor combustion. + +\section*{Sensing concept} + +The proposed sensing chain is: + +\[ +\text{Flame emission} +\rightarrow +\text{UV/visible optical filter} +\rightarrow +\text{photodiode} +\rightarrow +\text{TIA} +\rightarrow +\text{gain/filtering} +\rightarrow +\text{ADC/DSP} +\] + +A simple photodiode TIA has already been tested with flame sources in the UV region. +The observed response confirms that the required optical signal is detectable using +low-cost analogue electronics. This gives a practical development path: + +\[ +\text{IR flame PCB} +\rightarrow +\text{UV flame PCB} +\rightarrow +\text{dual-channel OH*/CH* diagnostic sensor} +\] + +This is an incremental development, not a new platform from scratch. + +\clearpage + +\section*{Diagnostic value} + +The proposed sensor could provide: + +\begin{itemize} + \item flame presence detection; + \item flame stability / flicker analysis; + \item rich/lean indication from the $OH^*/CH^*$ ratio; + \item early warning of poor combustion before conventional limits are reached; + \item possible correlation with NOx-forming conditions; + \item service and commissioning diagnostics; + \item with the addition of Swan bands ($C_2$), early indication of soot-forming conditions; + \item ratios and strengths of $OH^*$, $CH^*$ and $C_2$ may provide insight into the instantaneous composition of waste or syngas fuels. +\end{itemize} + +It should be stressed that this sensor does not directly measure CO or oxygen +concentration. Its value is as a complementary combustion-quality sensor, especially +where fast optical response provides information that slower gas probes may not. + +\section*{Additional advantages} + +\begin{itemize} + +\item \textbf{Fast response:} The optical signal is generated directly at the reaction zone and is not subject to transport delay. + +\item \textbf{Non-intrusive measurement:} No insertion into the flame or flue is required. + +\item \textbf{Harsh environment suitability:} Optical sensing may be more robust than conventional probes in high-temperature or contaminated conditions. + +\item \textbf{Early fault detection:} Chemiluminescence changes may precede measurable CO or O$_2$ changes. + +\item \textbf{Dynamic information:} Temporal behaviour (oscillation, intermittency) becomes observable. + +\item \textbf{Independent channel:} Provides plausibility checking against existing sensors. + +\item \textbf{Low-cost replication:} Additional channels can be added at low cost. + +\item \textbf{Variable fuel suitability:} Particularly relevant for syngas and mixed fuels. + +\item \textbf{Degradation monitoring:} Optical fouling may be inferred from signal changes. + +\end{itemize} + +\clearpage + +\section*{Commissioning support} + +In industrial burner systems, commissioning involves stepping through firing rates +and storing actuator positions (fuel valve, fan VSD). The aim is stable operation +across the full range. + +Currently this relies on: +\begin{itemize} + \item visual flame observation; + \item flue gas measurements (O$_2$, CO); + \item operator judgement. +\end{itemize} + +These do not directly observe the reaction zone. + +The proposed sensor could: + +\begin{itemize} + \item provide real-time flame quality at each firing point; + \item identify marginal or poorly mixed conditions; + \item optimise fuel/air settings based on flame behaviour; + \item improve repeatability; + \item enable semi-automated commissioning using metrics such as $OH^*/CH^*$ and signal stability. +\end{itemize} + +This extends the concept from monitoring to active commissioning support. + +% -------- Research section (conditional) -------- +\ifresearch + +\clearpage +\section*{Research questions} + +\begin{itemize} + +\item \textbf{Information content:} +What combustion state information is recoverable from multi-band chemiluminescence? + +\item \textbf{Separability:} +Can fuel effects be distinguished from air setting, turbulence, and fouling? + +\item \textbf{Dynamics:} +Do temporal statistics indicate instability or blow-off proximity? + +\item \textbf{Fuel inference:} +Can variable fuels (e.g. syngas) be characterised indirectly? + +\item \textbf{Robustness:} +How sensitive are results to burner geometry and viewing conditions? + +\item \textbf{Implementation:} +Is low-cost photodiode hardware sufficient for industrial deployment? + +\end{itemize} + +\fi + +\section*{Proposed next step} + +Build a multi-channel demonstrator including: + +\[ +\SI{310}{nm}\ \ce{OH^{*}} \quad \text{and} \quad \SI{430}{nm}\ \ce{CH^{*}} +\] + +Additional channels may include: +\begin{itemize} + \item broadband visible; + \item green-filtered ($C_2$ Swan band); + \item broadband IR. +\end{itemize} + +The selected microcontroller provides sufficient ADC channels and DSP capability. +Each IR channel requires one op-amp, while each UV channel requires two, which remains +compatible with the current architecture. + +\end{document} \ No newline at end of file diff --git a/papers/proposals/syngas_chemilumesence.tex b/papers/proposals/syngas_chemilumesence.tex new file mode 100644 index 0000000..7a7117e --- /dev/null +++ b/papers/proposals/syngas_chemilumesence.tex @@ -0,0 +1,164 @@ +\documentclass[10pt,a4paper]{article} + +\usepackage[margin=18mm]{geometry} +\usepackage{amsmath} +\usepackage{siunitx} +\usepackage{graphicx} + +\title{\vspace{-1.0cm}Optical Chemiluminescence Diagnostics for Syngas Composition and Combustion State} +\author{Robin Clark} +\date{} + +\begin{document} +\maketitle +\vspace{-0.8cm} + +\section*{Abstract} + +This note proposes a non-intrusive optical method for assessing syngas composition and combustion quality using flame chemiluminescence. +By observing emission from excited radicals (OH*, CH*, and C$_2$), it is possible to infer air--fuel ratio, combustion stability, and the presence of carbon-rich species. +The approach is intended as a fast, low-cost diagnostic layer rather than a replacement for conventional gas analysis. The concept is well suited to structured investigation as a PhD topic. + +\section*{1. Motivation} + +Syngas composition varies significantly depending on feedstock and gasifier conditions, typically comprising mixtures of H$_2$, CO, CH$_4$, CO$_2$, and N$_2$. + Conventional measurement techniques (e.g. NDIR, TCD, lambda probes) are often: + +\begin{itemize} +\item intrusive or require gas sampling, +\item relatively slow, +\item costly in industrial environments. +\end{itemize} + +There is therefore value in a real-time, in-situ diagnostic method based on combustion behaviour. + +\section*{2. Principle} + +During combustion, short-lived excited radicals emit light at characteristic wavelengths: + +\begin{center} +\begin{tabular}{l l l} +\textbf{Species} & \textbf{Wavelength} & \textbf{Interpretation} \\ +\hline +OH* & $\sim$310 nm & Oxidation zone / flame front \\ +CH* & $\sim$430 nm & Hydrocarbon breakdown \\ +C$_2$ (Swan bands) & $\sim$516 nm & C--C chemistry / soot precursors\\ +\end{tabular} +\end{center} + +These emissions arise from reaction~kinetics and flame~chemistry rather than bulk temperature alone, making them sensitive to both mixture and fuel composition. + +\section*{3. Core Measurement Concept} + +The approach is based on measuring intensity ratios: + +\begin{align} +R_1 &= \frac{\text{OH}^*}{\text{CH}^*} \quad \text{(air--fuel ratio)} \\ +R_2 &= \frac{\text{C}_2^*}{\text{CH}^*} \quad \text{(hydrocarbon richness)} \\ +R_3 &= \frac{\text{C}_2^*}{\text{OH}^*} \quad \text{(soot tendency)} +\end{align} + +In addition, temporal behaviour provides diagnostic information: + +\begin{itemize} +\item Standard deviation of OH* intensity $\rightarrow$ flame stability +\item Cross-correlation between bands $\rightarrow$ regime transitions +\end{itemize} + +\section*{4. Role of C$_2$ Chemiluminescence} + +The inclusion of C$_2$ (Swan bands) is key to extending the method beyond conventional OH*/CH* sensing.~\footnote{C$_2$ chemiluminescence (Swan bands, $\sim$516~nm) is typically observed in fuel-rich or locally oxygen-limited regions of hydrocarbon flames. In these conditions, oxidation of carbon fragments is inhibited and radical recombination pathways dominate, leading to formation of C$_2$ via reactions such as C + CH $\rightarrow$ C$_2$ + H. Excited C$_2^*$ species emit banded radiation as they relax, producing the characteristic green Swan bands. The presence of C$_2$ is therefore indicative of carbon--carbon bond formation and is closely associated with the early stages of soot precursor development.} + +\subsection*{4.1 Physical Significance} + +C$_2$ emission is associated with: + +\begin{itemize} +\item presence of C--C bonds, +\item locally fuel-rich regions, +\item formation of soot precursors. +\end{itemize} + +\subsection*{4.2 Diagnostic Value} + +\begin{center} +\begin{tabular}{l c c c l} +\textbf{Condition} & OH & CH & C$_2$ & \textbf{Interpretation} \\ +\hline +H$_2$-rich gas & High & Low & $\approx$0 & Clean combustion \\ +CO/H$_2$ mix & Moderate & Low & $\approx$0 & Typical syngas \\ +CH$_4$ present & Moderate & High & Low--mod & Methane content \\ +Heavy HC / tar & Lower & High & High & Soot risk / contamination \\ +\end{tabular} +\end{center} + +Thus, C$_2$ provides sensitivity to carbon chemistry and enables discrimination between different syngas compositions. + +\section*{5. Additional Spectral Features} + +Other emissions of potential interest include: + +\begin{itemize} +\item CN bands ($\sim$388 nm): nitrogen-containing species +\item Na/K lines ($\sim$589 nm): contaminants or ash +\item Continuum emission: soot radiation and incomplete combustion +\end{itemize} + +A multi-band or spectrally resolved approach may allow further discrimination using statistical or machine learning techniques. + +\section*{6. Implementation} + +A practical system could consist of: + +\begin{itemize} +\item Photodiodes with narrow bandpass filters (310 nm, 430 nm, 516 nm) +\item Transimpedance amplifiers (TIA front-end) +\item ADC and embedded processing (e.g. STM32 class device) +\end{itemize} + +Signal processing would include averaging, ratio calculation, and temporal analysis. + +\section*{7. Applications} + +Potential applications include: + +\begin{itemize} +\item Gasifier monitoring +\item Industrial burner optimisation +\item Detection of: + \begin{itemize} + \item flame instability, + \item soot formation, + \item poor mixing or fuel variation, + \item inference of calorific value (subject to calibration against gas composition) + \end{itemize} +\end{itemize} + +\section*{8. Research Opportunity} + +Key open questions suitable for PhD investigation include: + +\begin{itemize} +\item Calibration of optical signals against known gas compositions +\item Sensitivity to temperature and pressure variations +\item Robustness under optical fouling +\item Extension to spectrally resolved measurement +\end{itemize} + +\section*{9. Conclusion} + +Multi-band chemiluminescence sensing offers a promising route to fast, non-intrusive diagnostics for syngas combustion. +The addition of C$_2$ emission provides a potentially valuable link to fuel composition, +extending the method beyond simple air--fuel ratio measurement. +The concept warrants structured experimental validation and is well suited to academic--industrial collaboration. + +\section*{10. Proposed Work (Outline)} + +\begin{itemize} +\item Controlled combustion experiments with known gas mixtures +\item Multi-band optical measurement and calibration +\item Development of regression models for composition and calorific value +\item Validation under real-world conditions (optical fouling, turbulence) +\end{itemize} + +\end{document} \ No newline at end of file