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Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
The staged combustion cycle provides the highest performance of conventional chemical rocket engines. Turbine power is derived from a separate combustor or preburner which also utilizes the same propellants as the main system. In bipropellant systems, the hot gas is routed through the turbopump turbines to the main injector where it is mixed with the other propellant and is combusted in the main chamber Pump discharge pressures are set by chamber pressure plus pressure losses in the cooling circuit, turbine, injector, valves, and ducting. Thrust chambers are regeneratively cooled. Staged combustion cycle engines developed in the U.S. have utilized a fuel-rich preburner. Several rocket engine systems developed in Russia have utilized an oxidizer-rich preburner. In the former case, the fuel-rich hot gases are mixed with oxidizer in the main chamber. In the latter, oxidizer-rich hot gases are mixed with fuel in the main chamber. The staged combustion cycle utilizes all propellants in the main combustion chamber, which provides maximum performance. A schematic of a simple staged combustion system is given in Figure 197.4.
Pollutant Formation and Methods of Control
Published in A. Williams, M. Pourkashanian, J. M. Jones, N. Skorupska, Combustion and Gasification of Coal, 2018
A. Williams, M. Pourkashanian, J. M. Jones, N. Skorupska
Since oxygen atom concentrations and flame temperatures are low in fuel-rich stoichiometric situations, a number of NOx control methods have attempted to adopt this technique. Generally, this involves two-stage (staged) combustion; the first stage of combustion is undertaken under rich conditions and in the second stage additional air is added to complete combustion. In this way the oxygen atom concentration as well as the peak temperature is reduced, and thus the rate of NO formation is reduced. However, a major difficulty is that there is a tendency for soot to be formed and considerable care has to be exercised in its application. In continuous-flow combustion chambers such as furnaces and boilers, this method is readily applied by operating one or more burners rich and adding additional air later on. This is also a form of staged combustion. Alternatively, in multiburner arrays some burners are run rich and other burners are used to provide the additional air. A variation of two-stage combustion is “reburn” in which the last stage is run rich either by coal particle injection or natural gas injection. The rich fuel components (CH, CH3, etc.) react with the NO reducing it to N2 via R3.16, namely, CH,CH3+NO=HCN+H,H2OHCCO+NO=CN+CO2atlowtemperature
A simplified two-mixture-fraction-based flamelet modelling and its validation on a non-premixed staged combustion system
Published in Combustion Theory and Modelling, 2023
Various new combustion technologies are being developed to meet the increasingly stringent regulations, in which multiple-stream injection strategies, for instance, a secondary air introduced gas turbine [1–3], have attracted significant attention. This kind of process is called staged combustion, in which the burning first takes place in the upper fuel-rich stage, and a secondary oxidiser is added in the second stage to consume the fuel. Besides the merits, these new technologies introduce new challenges in the design process of the systems. Numerical simulations are no doubt a powerful tool that can assist to address these challenges, as well as to gain deep insights into the combustion fundamentals. In terms of combustion numerical simulation, flamelet-based models [4–6] are appealing chemistry models, owing to their simplicity and great improvements over the fast chemistry assumption [7]; they enable the use of detailed chemical mechanisms at modest computational cost by storing flamelet states prior to simulation.
Trends in onroad transportation energy and emissions
Published in Journal of the Air & Waste Management Association, 2018
The mix of fuel delivery systems for new U.S. LDVs is undergoing dramatic changes with the rapid emergence of GDI. In the last 10 years, GDI has gained a growing share of the U.S. market, now exceeding 50% of new LDV sales (EPA 2016e). GDI delivers fuel directly into the cylinder, thereby eliminating fuel transport delay and enabling very precise control of timing and air/fuel ratio. Fuel can be delivered to better match engine load and with more than one injection pulse to achieve staged combustion (Zhao, Lai, and Harrington 1999). Staged combustion helps prevent knock, which enables an increase in compression ratio for improved engine efficiency. Estimates of the fuel economy advantage of GDI engine LDVs versus those with port fuel injection (PFI) range from 1.5% to 30% (NRC 2015). Spray-guided systems, which are referred to as second-generation GDI, produce fewer particles than the first-generation wall-guided systems (Short et al. 2017). This is largely because fuel spray in wall-guided systems impinges on piston and cylinder surfaces more so than for spray-guided systems, which leads to cooling of the fuel spray and more particle formation (Seo et al. 2016).