Combustion in the future: The importance of chemistry

Combustion involves chemical reactions that are often highly exothermic. Combustion systems utilize the energy of chemical compounds released during this reactive process for transportation, to generate electric power, or to provide heat for various applications. Chemistry and combustion are interlinked in several ways. The outcome of a combustion process in terms of its energy and material balance, regarding the delivery of useful work as well as the generation of harmful emissions, depends sensitively on the molecular nature of the respective fuel. The design of efficient, low-emission combustion processes in compliance with air quality and climate goals suggests a closer inspection of the molecular properties and reactions of conventional, bio-derived, and synthetic fuels. Information about flammability, reaction intensity, and potentially hazardous combustion by-products is important also for safety considerations. Moreover, some of the compounds that serve as fuels can assume important roles in chemical energy storage and conversion. Combustion processes can furthermore be used to synthesize materials with attractive properties. A systematic understanding of the combustion behavior thus demands chemical knowledge. Desirable information includes properties of the thermodynamic states before and after the combustion reactions and relevant details about the dynamic processes that occur during the reactive transformations from the fuel and oxidizer to the products under the given boundary conditions. Combustion systems can be described, tailored, and improved by taking chemical knowledge into account. Combining theory, experiment, model development, simulation, and a systematic analysis of uncertainties enables qualitative or even quantitative predictions for many combustion situations of practical relevance. This article can highlight only a few of the numerous investigations on chemical processes for combustion and combustion-related science and applications, with a main focus on gas-phase reaction systems. It attempts to provide a snapshot of recent progress and a guide to exciting opportunities that drive such research beyond fossil combustion.

Keywords: 2M2B, 2-methyl-2-butene; AFM, atomic force microscopy; ALS, Advanced Light Source; APCI, atmospheric pressure chemical ionization; ARAS, atomic resonance absorption spectroscopy; ATcT, Active Thermochemical Tables; BC, black carbon; BEV, battery electric vehicle; BTL, biomass-to-liquid; Biofuels; CA, crank angle; CCS, carbon capture and storage; CEAS, cavity-enhanced absorption spectroscopy; CFD, computational fluid dynamics; CI, compression ignition; CRDS, cavity ring-down spectroscopy; CTL, coal-to-liquid; Combustion; Combustion chemistry; Combustion diagnostics; Combustion kinetics; Combustion modeling; Combustion synthesis; DBE, di-n-butyl ether; DCN, derived cetane number; DEE, diethyl ether; DFT, density functional theory; DFWM, degenerate four-wave mixing; DMC, dimethyl carbonate; DME, dimethyl ether; DMM, dimethoxy methane; DRIFTS, diffuse reflectance infrared Fourier transform spectroscopy; EGR, exhaust gas recirculation; EI, electron ionization; Emissions; Energy; Energy conversion; FC, fuel cell; FCEV, fuel cell electric vehicle; FRET, fluorescence resonance energy transfer; FT, Fischer-Tropsch; FTIR, Fourier-transform infrared; Fuels; GC, gas chromatography; GHG, greenhouse gas; GTL, gas-to-liquid; GW, global warming; HAB, height above the burner; HACA, hydrogen abstraction acetylene addition; HCCI, homogeneous charge compression ignition; HFO, heavy fuel oil; HRTEM, high-resolution transmission electron microscopy; IC, internal combustion; ICEV, internal combustion engine vehicle; IE, ionization energy; IPCC, Intergovernmental Panel on Climate Change; IR, infrared; JSR, jet-stirred reactor; KDE, kernel density estimation; KHP, ketohydroperoxide; LCA, lifecycle analysis; LH2, liquid hydrogen; LIF, laser-induced fluorescence; LIGS, laser-induced grating spectroscopy; LII, laser-induced incandescence; LNG, liquefied natural gas; LOHC, liquid organic hydrogen carrier; LT, low-temperature; LTC, low-temperature combustion; MBMS, molecular-beam MS; MDO, marine diesel oil; MS, mass spectrometry; MTO, methanol-to-olefins; MVK, methyl vinyl ketone; NOx, nitrogen oxides; NTC, negative temperature coefficient; OME, oxymethylene ether; OTMS, Orbitrap MS; PACT, predictive automated computational thermochemistry; PAH, polycyclic aromatic hydrocarbon; PDF, probability density function; PEM, polymer electrolyte membrane; PEPICO, photoelectron photoion coincidence; PES, photoelectron spectrum/spectra; PFR, plug-flow reactor; PI, photoionization; PIE, photoionization efficiency; PIV, particle imaging velocimetry; PLIF, planar laser-induced fluorescence; PM, particulate matter; PM10 PM2,5, sampled fractions with sizes up to ∼10 and ∼2,5 µm; PRF, primary reference fuel; QCL, quantum cascade laser; RCCI, reactivity-controlled compression ignition; RCM, rapid compression machine; REMPI, resonance-enhanced multi-photon ionization; RMG, reaction mechanism generator; RON, research octane number; Reaction mechanisms; SI, spark ignition; SIMS, secondary ion mass spectrometry; SNG, synthetic natural gas; SNR, signal-to-noise ratio; SOA, secondary organic aerosol; SOEC, solid-oxide electrolysis cell; SOFC, solid-oxide fuel cell; SOx, sulfur oxides; STM, scanning tunneling microscopy; SVO, straight vegetable oil; Synthetic fuels; TDLAS, tunable diode laser absorption spectroscopy; TOF-MS, time-of-flight MS; TPES, threshold photoelectron spectrum/spectra; TPRF, toluene primary reference fuel; TSI, threshold sooting index; TiRe-LII, time-resolved LII; UFP, ultrafine particle; VOC, volatile organic compound; VUV, vacuum ultraviolet; WLTP, Worldwide Harmonized Light Vehicle Test Procedure; XAS, X-ray absorption spectroscopy; YSI, yield sooting index.