S. O. Bade Shrestha

Predicting the effects of the presence of diluents with methane on spark ignition engine performance

The presence of diluents with methane, which is often encountered in practice, brings about significant changes in the combustion process in engines and undermines performance. This paper describes an analytical approach for predicting the effects of the presence of diluents with methane on spark ignition engine performance. Calculated values of power output for a range of diluent concentrations in the fuel mixtures are shown for various operating conditions. The agreement between predicted and the corresponding experimental values was found to be especially good when the fractional concentration of the diluent in the fuel is lower than about 50%. Better agreement was also obtained with cases involving nitrogen relative to those with carbon dioxide.

A Thermodynamic Analysis of the Rich Flammability Limits of Fuel-Diluent Mixtures in Air

A simple approach is described for the calculation of the rich flammability limits of fuel-diluent mixtures in air for a wide range of initial temperatures based only on the knowledge of the flammability limit of the pure fuel in air at atmospheric temperature and pressure conditions. Various fuel-diluent mixtures that include the fuels methane, ethylene, ethane, propane, butane, carbon monoxide, and hydrogen, and the diluents nitrogen, carbon dioxide, helium, and argon have been considered. Good agreement is shown to exist between predicted values of the rich flammability limits and the corresponding available experimental values for the fuel-diluent mixtures.

Effects of diluents on knock rating of gaseous fuels

Abstract Concerns on energy security, emissions, and the recent hike in the price of fossil fuels have prompted the rapidly growing interest in the use of various alternative and renewable fuels, including low heating value fuels such as land-filled gases, biogases, coal bed methane gases, and others. Generally, the low heating value (btu) fuels contain substantial amounts of diluents such as carbon dioxide, nitrogen, water vapour, and other trace gases in the fuel composition. The present contribution describes the results of the investigation of knock in a single-cylinder variable compression ratio (CR) spark-ignition engine fuelled with gaseous fuels, such as natural gas, methane, and hydrogen, in the presence of different amounts of diluents, specifically carbon dioxide and nitrogen, in the fuel mixture in order to represent closely the general composition of land filled and biogases in practice. The knock characteristics of the fuels were quantitatively evaluated in terms of the methane number using various methods. Generally, the addition of either diluent carbon dioxide or nitrogen in the fuel mixtures augmented the knock resistance characteristics extending the engine operational limits. With every 10 per cent increase of carbon dioxide in the fuel mixture, the CR was increased by one point, whereas for a 25 per cent of nitrogen content in the fuel mixture, the CR was augmented by a half point in the operating conditions considered.

The Operational Mixture Limits in Engines Fueled With Alternative Gaseous Fuels

The operation of engines whether spark ignition or compression ignition on a wide range of alternative gaseous fuels when using lean mixtures can offer in principle distinct advantages. These include better economy, reduced emissions, and improved engine operational life. However, there are distinct operational mixture limits below which acceptable steady engine performance cannot be sustained. These mixture limits are usually described as the “lean operational limits,” or loosely as the ignition limits which are a function of various operational and design parameters for the engine and fuel used. Relatively simple approximate procedures are described for predicting the operational mixture limits for both spark ignition and dual fuel compression ignition engines when using a range of common gaseous fuels such as natural gas/methane, propane, hydrogen, and some of their mixtures. It is shown that good agreement between predicted and corresponding experimental values can be obtained for a range of operating conditions for both types of engines.

Evaluation of the Performance Characteristics and Modeling of an Alkaline Fuel Cell

Alkaline fuel cells are one of the low cost types of fuel cells. In this contribution, the performance of an alkaline fuel cell was investigated by varying different operational parameters. The cell was tested under four different electrolyte concentrations and three different levels of anode flow rates. The results of the test revealed that the efficiency of the cell increases with the increase in electrolyte concentration. Anode flow rate was not found to have a considerable impact on the cell performance. Impedance spectroscopy has been conducted to validate the mathematical model and further investigate ohmic resistance, anode and cathode activation losses and mass transport losses. The optimal level of electrolyte concentration and anode flow rate for an alkaline fuel cell has been deduced through modeling & statistical analysis.Copyright

Review of Numerical Modeling and Simulation Results Pertaining to High-speed Combustion in Scramjets

This paper is a review of numerical modeling of high-speed combustion as it pertains to scramjets. Simulation results are presented from numerous researchers that have devoted their time and effort to numerically investigate high-speed combustion in scramjets. In addition to their findings validation work is presented, showing the validity of ANSYS Fluent 12.1 in the application of high-speed combustion in scramjets.

Landfill gas - A fuel for IC engine applications

Landfill gases and biogases are low Btu gases which were, until recently, underutilized. However interest on the utilization of these gases for energy production has been increasing due to environment concerns and global warming caused by burning fossil fuels, energy security concerns and renewable nature of these gases. The main portion of landfill gas or biogas is comprised of methane and carbon dioxide with some other gases in small proportions. Release of methane directly to the atmosphere causes about 21 times global warming effects than carbon dioxide. Thus landfill gas is flared often, where the energy recovery is not economically viable in practice. Using landfill gas to generate energy encourages more efficient collection reducing emissions into the atmosphere and generates revenues for the operators. However the use of landfill gases for electricity generation is not perceived as an attractive option because of some disadvantages. Thus it becomes necessary to address disadvantages involved by studying the landfill gases in a technological perspective and motivate the utilization of the landfill gas for the future energy needs. This paper discussed landfill gas as a fuel for a spark ignition engine to produce power in an effective way and effects of additions of a small quantity of hydrogen in the fuel mixtures. The effect of the composition changes in landfill gases on the performance of the engine is also presented.© 2007 ASME

Boundary layer combustion for skin friction drag reduction in scramjet combustors

A parametric study was conducted for flow over a heated flat plate using ANSYS Fluent 14.5. The incoming flow had a Mach number of 6, static temperatue 300 K, and total pressure of 1 MPa. The study involved cases with and without fuel injection. Hydrogen and JP-10 fuels were tested, using a chemical reaction mechanism from CHEMKIN. The simulation results showed hydrogen to be a more effective fuel to use in order to achieve skin friction reduction through boundary layer combustion than JP-10. There was an approximate 50% reduction in the skin friction coefficient as a result of hydrogen injection and combustion in the boundary layer.

Experimental Investigation of a Passive Direct Methanol Fuel Cell

Direct methanol fuel cells (DMFC) are getting increasing attention as a possible power source for application in the field of power electronics where the energy requirements are relatively small. The major advantage of the DMFC is their high energy density in comparison to the conventional batteries. In this study, the performance of a passive direct methanol fuel cell was investigated under five different methanol concentrations. To further investigate various losses in the fuel cell, impedance spectroscopy was employed to measure ohmic, activation and mass transport losses for all concentrations. It was observed that the performance of the fuel cell improved while the concentration of methanol solutions was closer to its corresponding stoichiometric values. Similarly, the temperature of the fuel cell was found to be higher as methanol concentration increases.

Hydrogen as an additive to methane for spark ignition engine applications

It is shown that the performance of a gas fuelled spark ignition engine can be enhanced considerably when relatively small amounts of hydrogen are present with methane. This improvement in performance which is especially pronounced at operational equivalence ratios that are much leaner than the stoichiometric value, can be attributed largely to the faster and cleaner burning characteristics of hydrogen in comparison to methane. Through analytical simulation of engine performance, the addition of hydrogen is considered through its production in-situ on board the engine by electrolysis of water with the necessary energy supplied from engine power. It is shown that when the work energy required for the production of hydrogen by electrolysis is taken into account, the range of viable operation of such an engine is very narrow. This would render the whole concept of in situ hydrogen production through water electrolysis uneconomical in conjunction with engine operation, even though the presence of additional oxygen produced with the hydrogen tends, in principle, to improve engine performance beyond that observed with hydrogen addition.