Estimation of Wiebe Function Parameters for Syngas and Anode Off-Gas Combustion in Spark-Ignition Engines

Wiebe functions, analytical equations that estimate the fuel mass fraction burned (MFB) during combustion, have been effective at describing spark-ignition (SI) engine combustion using gasoline fuels. This study explores if the same methodology can be extended for SI combustion with syngas, a gaseous fuel mixture composed of H2, CO, and CO2, and anode-off gas; the latter is an exhaust gas mixture emitted from the anode of a Solid Oxide Fuel Cell, containing H2, CO, H2O, and CO2. For this study, anode off-gas is treated as a syngas fuel diluted with CO2 and vaporized water. Combustion experiments were run on a single-cylinder, research engine using syngas and anode-off gas as fuels. One single Wiebe function and three double Wiebe functions were fitted and compared with the MFB profile calculated from the experimental data. It was determined that the SI combustion process of both the syngas and the anode-off gas could be estimated using a governing Wiebe function. While the detailed double Wiebe function had the highest accuracy, a reduced double Wiebe function is capable of achieving comparable accuracy. On the other hand, a single Wiebe function is not able to fully capture the combustion process of a SI engine using syngas and anode off-gas.

Empirical investigation of spark-ignited flame-initiation cycle-to-cycle variability in a homogeneous charge reciprocating engine

This experimental study investigates the flame-initiation period variability in the spark-ignited homogeneous charge third-generation transparent combustion chamber optical engine. The engine was operated with lean, rich, and stoichiometric, propane and methane, with and without nitrogen dilution. These operating conditions were chosen to systematically change the unstretched laminar flame velocity and the Markstein number. Traditional pressure measures, apparent heat release analysis, particle image velocimetry, and OH* flame imaging were used to generate over 400 metrics for 750 cycles at each of the 34 tests at 11 operating conditions. A multivariate statistical analysis was used to identify the parameters important to the variability of the crank angle at 10% fuel mass fraction burned but could not reveal physical mechanisms or cause and effect. The analysis here revealed that the combustion-phasing cycle-to-cycle variability is established by the time of the notional laminar-to-turbulent flame transition that occurs by 1% mass burn fraction, measured here from the flame image growth. Both the Markstein number and stretched laminar flame speed were found to be important. The velocity magnitude and direction were found to correlate with fast and slow 10% fuel mass fraction burned as found in early literature. It was also revealed that the shear strength, a property of the strain rate tensor at the scales resolved here (1 mm), deserves further investigation as a possible effect on 10% fuel mass fraction burned.

Re-ignition of multi-species soot clouds in building fires

The re-ignition potential of multi-species soot clouds in building fires were investigated based on their extinction characteristics. The investigation was carried out theoretically using the adaptation of Semenov`s thermal explotion theory. The critical sizes of soot particles in the cloud were found to be strongly effected by the particle temperature., shape, and reactivity, as the mass fraction of each species, and ambient conditions. The clous shape, cloud particle number density, fuel mass fraction and soot reactivity were identified as the major parameters impacting upon the cloud extinction potential. Our analysis indicate that blending of a base soot with a less reactive soot generally increases extinction potential of the cloud ( i.e. likelihood of extinction) while addition of a more reactive secondary soot to the base one minimizes the probability of cloud extinction.Keywords: extinction, clouds, re-ignition, soot

Combustion Characteristic of a Diesel Engine Operating with Methanol as Alternative Fuel

Modelling the compression ignition engine mostly depends on fuel characteristics. The proses involve a model of the real system and carry out experiment as a mean of comparison to understand the behaviour of the system. The diesel engine nowadays operated with different kind of alternative fuels such as natural gas and biofuel. The aim of this article is to study the combustion characteristic occurred in an engine cylinder of a diesel engine when using biofuel. The one-dimensional numerical analysis using GT-Power software is used to simulate the diesel engine. The engine operated at full engine load and difference speed. The methanol fuel used in the simulation is derived from the conventional methanol fuel properties. The analysis of simulations includes the cylinder pressure, combustion temperature and rate of heat release. The simulation result shows that in-cylinder pressure for methanol is slightly higher than diesel fuel in any speed of the engine. It also found that the combustion characteristic on methanol temperature is higher at all crank angle degree of diesel fuel. Mass fraction burns of methanol are much lower than diesel fuel, but burns faster than diesel fuel.

Effects of CO2 dilution on combustion instabilities in dual premixed flames

There has been a rapid increase in the demand for biogas applications in recent years, and dry low NOx and dry low emission gas turbine combustors are promising platforms for such applications. Combustion instability is the most important drawback in dry low NOx gas turbine combustors and has, therefore, attracted considerable research interest lately. As a fundamental study towards the use of biogas in dry low NOx and dry low emission gas turbine combustors, this article investigates the influence of CO2 in surrogate biogas on combustion instability. Tests were conducted using a dry low NOx type, a dual lean premixed gas turbine combustor. For a dual flame with dual swirl, the pilot fuel mass fraction affects the flame structure, and the flame structure, in turn, determines the temperature distribution in the combustion chamber and the combustion instability. The effects of the pilot fuel mass fraction, which is an important parameter of the combustor, and the CO2 dilution rate, which is a major contributor of biogas combustion, on the combustion characteristics and instability are investigated through dynamic pressure signal and phase-resolved OH* images. Combustion instability decreases for higher CO2 dilution rates, whose effects depend on the pilot fuel mass fraction. The instability reaches its maximum at a pilot fuel mass fraction of 0.3. Tests confirm that combustion instability diminishes with CO2 dilution, as it reduces the perturbation in the heat emission, and the flame speed decreases resulting in a greater flame surface or volume. Further, investigation of the Rayleigh Index, which represents the coupling strength of the heat release fluctuation and the natural frequency, shows that CO2 dilution weakens the coupling strength, resulting in less combustion instability.

The Effect of Piston Bowl and Spray Configuration on Diesel Combustion and Emissions

A numerical and experimental study of the effect of piston bowl and spray configuration on diesel combustion and emissions has been conducted. The objective of this study is to gain better understanding of the effect of the piston bowl shape and fuel injector configuration on fuel-air mixing, combustion, and emissions in a diesel engine. Ideally, a uniform fuel-air mixture in the cylinder is desired to prevent the formation of regions containing a rich mixture, where soot is usually formed, and regions of lean mixtures, where nitrogen oxides are formed. Different piston bowl shapes and fuel injectors (number of nozzles, spray angle) have been considered and simulated using computational fluid dynamics and experiments. CFD calculations of fuel mass fraction, and measurements of cylinder pressure and emissions species are included. The results show that computer simulations coupled with experiments provide insight into the interactions between fluid flow, fuel-air mixing, combustion, and emissions.