Low temperature combustion (LTC) is a recent engine technology that can reduce the oxides of nitrogen (NOx) and soot emissions simultaneously while maintaining higher thermal efficiency. The present review work investigates the performance, emission and combustion characteristics of LTC mode engines. Partially premixed LTC (PPLTC), homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI) and reactivity controlled compression ignition (RCCI) modes are researched under LTC mode. In recent decades, different engine strategies have been employed to reduce exhaust emissions and to enhance thermal efficiency. Exhaust gas recirculation, variable valve timing (VVT), advanced fuel injection technologies are adapted to achieve LTC mode in internal combustion (IC) engines to get improved outcomes. This review highlights the properties of fuels, fuel supply systems, valve actuation mechanisms, engine operating conditions and its effects on the engine characteristics. This review provides a perspective plan to the researchers for enhancing the performance, emission and combustion behavior of an engine by using LTC mode with lower NOx and soot emissions. Among LTC mode engines, RCCI mode engine operates well in 60% load, 60% premixed ratio, 35:1 air-fuel ratio and 56% brake thermal efficiency within the combustion phasing control.

A review on low temperature combustion engines: Performance, combustion and emission characteristics

The mechanism of carbon particulate (soot) inception has been a subject of numerous studies and debates. The article begins with a critical review of prior proposals, proceeds to the analysis of factors enabling the development of a meaningful nucleation flux, and then introduces new ideas that lead to the fulfillment of these requirements. In the new proposal, a rotationally-activated dimer is formed in the collision of an aromatic molecule and an aromatic radical; the two react during the lifetime of the dimer to form a stable, doubly-bonded bridge between them, with the reaction rooted in a five-member ring present on the molecule edge. Several such reactions were examined theoretically and the most promising one generated a measurable nucleation flux. The consistency of the proposed model with known aspects of soot particle nanostructure is discussed. The foundation of the new model is fundamentally the H-Abstraction-Carbon-Addition (HACA) mechanism with the reaction affinity enhanced by rotational excitation.

On the mechanism of soot nucleation.

Soot inception: Carbonaceous nanoparticle formation in flames

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.

Combustion in the future: The importance of chemistry

The distillation curve and sooting propensity of a typical jet fuel

The effects of n -propylbenzene addition to n -dodecane on soot formation and aggregate structure in a laminar coflow diffusion flame is investigated. The goal is to gain insight on the influence of n -propylbenzene addition to n -dodecane on the underlying mechanisms of soot formation processes. The methane laminar coflow diffusion flame doped with pure n -dodecane establishes the base environment in this study. n -Propylbenzene is mixed into n -dodecane at three levels: 15%, 30% and 45% in mole fraction. The inlet total carbon flow rate is held constant for all of the flames. The combined laser extinction and two-angle elastic light scattering method is used to measure soot volume fraction, primary particle diameter and number density. As expected, soot volume fraction is shown to increase at all heights in the flames with increasing mole fraction of n -propylbenzene in the liquid fuel mixture. The differences in profiles of soot volume fraction suggest a non-linear relationship between the mole fraction of n -propylbenzene in the liquid fuel mixture and the increase in soot production. The relative importance of soot inception and surface growth affected by n -propylbenzene addition is shown to be different along the flame wing and centerline. Along the wing, the aromatic fuel molecular structure primarily influences the initial soot inception process at earlier times by providing a larger population of incipient soot particles for the subsequent surface growth. Along the centerline, the aromatic fuel chemistry effect is stronger, as it accelerates both the soot inception and the subsequent surface growth processes. The experimental data presented in this study is also useful for the validation of soot models of the liquid fuel surrogate components.

Effects of n-propylbenzene addition to n-dodecane on soot formation and aggregate structure in a laminar coflow diffusion flame

Understanding the formation and growth of polycyclic aromatic hydrocarbons (PAHs) and young soot from n-dodecane in a sooting laminar coflow diffusion flame

A numerical study of the effects of n-propylbenzene addition to n-dodecane on soot formation in a laminar coflow diffusion flame

Bluff body stabilised non-premixed flames are usually used as pilot flames in lean-premixed combustors. Experiments are conducted to investigate the characteristics of the flame. Typical flame modes are investigated in both stable and unstable conditions. The flow structures, the reaction zone, and the dynamics of unstable flames are measured with PIV, ICCD and a high speed camera, respectively, based on which the inherent mechanisms that influence the configuration and stabilisation of the flame are analysed. Stable flames are apparently influenced by the mixing characteristics in the recirculation zone. Flame detachment, a typical phenomenon of stable flames in a turbulent air flow, can be explained by the distribution of fuel concentration in the recirculation zone. The Reynolds number of air has different effects on different parts of the flame, which results in three unstable flame modes at different Reynolds numbers of air. These results could be helpful for the design of stable burners in practice.© 2013 ASME

Tongfeng Zhang

Papers

The distillation curve and sooting propensity of a typical jet fuel

Effects of n-propylbenzene addition to n-dodecane on soot formation and aggregate structure in a laminar coflow diffusion flame

Understanding the formation and growth of polycyclic aromatic hydrocarbons (PAHs) and young soot from n-dodecane in a sooting laminar coflow diffusion flame

A numerical study of the effects of n-propylbenzene addition to n-dodecane on soot formation in a laminar coflow diffusion flame

Characteristics of Flame Modes for a Conical Bluff Body Burner With a Central Fuel Jet