Fuel mixtures ratio

As the pressure is increased in a combustion system, the amount of dissociation decreases and the temperature rises, as shown in Fig. 6. This observation follows directly from Le Chatelier s principle. The effect is greatest, of course, at the stoichiometric air-fuel mixture ratio where the amount of dissociation is greatest. In a system that has little dissociation, the pressure effect on temperature... 

All stationary fuel users will ultimately convert their equipment to bum pipeline-supplied hydrogen. For natural gas users this will involve an adjustment of the air to fuel mixture ratio. Methane bums at a mixture ratio of one volume of methane to 10 volumes of air. One volume of hydrogen requires only 2.5 volumes of air. The gas flow orifice must be enlarged to allow the larger volumetric flow of... 

This air/fuel mixture ratio can be and is exploited in the control of internal combustion engines. For example, cars fitted with catalytic converters can operate with adjustable air/fuel ratio X, which allows the air/ fuel mixture to be optimized during the running of the engine, thus minimizing CO and hydrocarbon emissions. On the other hand, one should note that nitrogen oxides are not directly related to the air/fiiel mixture ratio, and thus cannot be controlled in this way. 

Fuel generation from CO2 on Ft nanoparticle catalysts may be used to produce fuels electrochemically in Mars missions, from ambient CO2 and water, both present in the atmosphere and soils on Mars [112]. Such fuels made onsite would enable Earth-return propellants and life-support consumables [157,158]. Sridhar and co-workers [158] proposed a new architecture for an in situ propellant production plant, which utilises solid oxide electrolysis to accomplish the combined electrolysis of water and carbon dioxide. This system produces methane by means of a Sabatier reactor and oxygen via electrolysis in the optimal oxidiser-to-fuel mixture ratio. It also has the capability to produce additional oxygen for life support needs. Results demonstrate that combined electrolysis enables a competitive system for in situ resource utilisation, and is easy to be scaled for sample return from Mars and for possible human missions to the planet [158]. 

Stoichiometry is the composition of the air-fuel mixture required to obtain complete combustion. The stoichiometric ratio, r, is the quotient of the respective masses, and m, of air and fuel arranged in the stoichiometric conditions ... 

In a general manner, diesel engines, jet engines, and domestic or industrial burners operate with lean mixtures and their performance is relatively insensitive to the equivalence ratio. On the other hand, gasoline engines require a fuel-air ratio close to the stoichiometric. Indeed, a too-rich mixture leads to an excessive exhaust pollution from CO emissions and unburned hydrocarbons whereas a too-lean mixture produces unstable combustion (reduced driveability and misfiring). 

Several parameters come into the relation between density and equivalence ratio. Generally, the variations act in the following sense a too-dense motor fuel results in too lean a mixture causing a potential unstable operation a motor fuel that is too light causes a rich mixture that generates greater pollution from unburned material. These problems are usually minimized by the widespread use of closed loop fuel-air ratio control systems installed on new vehicles with catalytic converters. 

During the determination of the RON, the CFR engine operates at 600 rpm with a timing advance set at 13° TDC and with no fuel mixture preheating. The MON by contrast operates at 900 rpm, with an advance from 14 to 26° depending on compression ratio and a fuei mixture temperature of 149°C. 

Products of Combustion For lean mixtures, the products of combustion (POC) of a sulfur-free fuel consist of carbon dioxide, water vapor, nitrogen, oxygen, and possible small amounts of carbon monoxide and unburned hydrocarbon species. Figure 27-12 shows the effect of fuel-air ratio on the flue gas composition resulting from the combustion of natural gas. In the case of solid and liquid fuels, the... 

Minimization of pollutants from the combustion chamber. This approach consists of designing the engine with improved fuel-air distribution systems, ignition timing, fuel-air ratios, coolant and mixture temperatures, and engine speeds for minimum emissions. The majority of automobiles sold in the United States now use an electronic sensor/control system to adjust these variables for maximum engine performance with minimum pollutant emissions. 

The firing controls that best ensure an air-rich mixture are often referred to as metering type controls, because gas flow and air flow are metered, thus the fuel-air ratio is controlled. The fuel-air ratio is the most important factor for safe, economical firing, so it is better to control it directly. Do not settle for low budget controllers that... 

H = visible flame height S = 2.3 X = flame speed = wind speed d = cloud depth g = gravitational acceleration po = fuel-air mixture density pj = density of air r = stoichiometric air-fuel mass ratio a = expansion ratio for stoichiometric combustion under constant pressure (typically 8 for hydrocarbons)... 

Calculate the stoichiometric air-fuel mass ratio, r, from the stoichiometric mixture composition, <(> and air and fuel molecular weights ... 

Calculate the air-fuel mass ratio r from the stoichiometric mixture composition < >j, and the densities of air and fuel ... 

For conventional gasoline, the stoichiometric ratio is approximately 14.7. Its precise value varies slightly with the composition of the gasoline. Maximum power is achieved with a slightly rich air/fuel ratio— say, 12.5. Maximum efficiency is achieved with a slightly lean mixture—say, 16—although this best-economy mixture ratio is somewhat dependent on combustion quality. 

The fact that the fuel/air ratio is spatially constant in HCSI engines, at least within a reasonably close approximation, allows substantial simplifications in combustion models. The burn rate or fuel consumption rate dm /dt is expressed as a function of flame surface area the density of the unburnt fuel/air mixture Pu, the laminar burning velocity Sl, and the fluctuations of velocities, i.e., E as a measure of turbulence, u. ... 

A 2-value smaller than 1 means that there is an excess of fuel in the mixture. In this case the air/fuel mixture is called rich. If more air is in the mixture than needed for a complete fuel combustion (2 > 1) the term lean mixture is used. Ideally the combustion is complete at 2 = 1. Real fuel cannot be combusted without an increase in CO and soot at 2-values smaller than 1.05. Due to changing operation conditions, for example a soiled burner, wear of the nozzle or leaky flaps, change of gas quality or changes of temperature and air pressure in the ambient atmosphere, the air/fuel ratio and thus flue gas composition can change over time. In order to minimize the risk of intoxication (see also chapter 5333), explosion and pollution real (uncontrolled) fuel burners are adjusted to operate far beyond this limit in the excess (lean mixture) region. However, unfortunately effi-... 

A complete chemical reaction in which no fuel and no oxygen is left is called a stoichiometric reaction. This is used as a reference, and its corresponding stoichiometric oxygen to fuel mass ratio, r, can be determined from the chemical equation. A useful parameter to describe the state of the reactant mixture is the equivalence ratio, d, defined as... 

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