Knock rating of gaseous fuels in a single cylinder spark ignition engine

This paper presents the determination of knock rating of gaseous fuels in a single cylinder engine. The first part of the work deals with an application of a standard method for the knock rating of gaseous fuels. The Service Methane Number (SMN) is compared with the standard Methane Number (MN) calculated from the standard AVL software METHANE (which corresponds to the MN measured on a Cooperative Fuel Research engine). Then, in the second part, the ‘mechanical’ resistance to knock of our engine is highlighted by means of the Methane Number Requirement (MNR). A single cylinder LISTER PETTER engine was modified to run as a spark ignition engine with a fixed compression ratio and an adjustable spark advance. Effects of engine settings on the MNR are deduced from experimental data and compared extensively with previous studies. Using the above, it is then possible to adapt the engine settings for optimal knock control and performances. The error on the SMN and MNR stands beneath ±2 MN units over the gases and engine settings considered.     

Preventive knock protection technique for stationary SI engines fuelled by natural gas

In a combined heat and power (CHP) plant, spark ignition engines must operate at their maximum power to reduce the pay back time. Because of environmental and economic concerns, engines are set with high compression ratios. Consequently, optimal operating conditions are generally very close to those of knock occurrence and heavy knock can severely damage the engine piston.There are two main protection techniques: the curative one commonly used by engine manufacturers and well documented in the literature and the preventive one based on a knock prediction according to the quality of the supplied gas. The indicator used to describe gas quality is the methane number (MN). The methane number requirement (MNR) of the engine is defined, for an engine set (spark advance, air-fuel ratio, and load), as the minimum value of MN above which knock free operation is ensured. To prevent knock occurrence, it is necessary to adapt the engine tuning according to variable gas composition. The objective of the present work is to validate the concept of knock preventive protection. First, a prediction of MNR according to engine settings (ES) is computed through a combustion simulator composed of a thermodynamic 2-zone model. Predicted MNR are compared to experimental results performed on a single-cylinder SI gas engine and show good agreement with numerical results (uncertainty below 1 point). Then, the combustion simulator is used to generate a protection mapping. At last, the knock preventive protection was successfully tested.     

Diesel and rapeseed methyl ester (RME) pilot fuels for hydrogen and natural gas dual-fuel combustion in compression-ignition engines

This paper presents experimental results of rapeseed methyl ester (RME) and diesel fuel used separately as pilot fuels for dual-fuel compression-ignition (CI) engine operation with hydrogen gas and natural gas (the two gaseous fuels are tested separately). During hydrogen dual-fuel operation with both pilot fuels, thermal efficiencies are generally maintained. Hydrogen dual-fuel CI engine operation with both pilot fuels increases NO_x emissions, while smoke, unburnt HC and CO levels remain relatively unchanged compared with normal CI engine operation. During hydrogen dual-fuel operation with both pilot fuels, high flame propagation speeds in addition to slightly increased ignition delay result in higher pressure-rise rates, increased emissions of NO_x and peak pressure values compared with normal CI engine operation. During natural gas dual-fuel operation with both pilot fuels, comparatively higher unburnt HC and CO emissions are recorded compared with normal CI engine operation at low and intermediate engine loads which are due to lower combustion efficiencies and correspond to lower thermal efficiencies. This could be due to the pilot fuel failing to ignite the natural gas-air charge on a significant scale. During dual-fuel operation with both gaseous fuels, an increased overall hydrogen-carbon ratio lowers CO₂ emissions compared with normal engine operation. Power output (in terms of brake mean effective pressure, BMEP) as well as maximum engine speed achieved are also limited. This results from a reduced gaseous fuel induction capability in the intake manifold, in addition to engine stability issues (i.e. abnormal combustion). During all engine operating modes, diesel pilot fuel and RME pilot fuel performed closely in terms of exhaust emissions. Overall, CI engines can operate in the dual-fuel mode reasonably successfully with minimal modifications. However, increased NO_x emissions (with hydrogen use) and incomplete combustion at low and intermediate loads (with natural gas use) are concerns; while port gaseous fuel induction limits power output at high speeds.     

Biofuel potential production from cottonseed oil: A comparison of non-catalytic and catalytic pyrolysis on fixed-fluidized bed reactor

Conversion of vegetable oils predominantly composed of triglycerides using pyrolysis type reactions represents a promising option for the production of renewable fuels and chemicals. The purpose of this article was to compare catalytic cracking with thermal cracking on production of gaseous hydrocarbon and gasoline conversion by cottonseed oil, and to discuss the difference on composition of products from catalytic cracking and thermal cracking. Reaction products are heavily dependant on the catalyst type (catalyst activation) and reaction conditions. They can range from dry gas to light distillate, such as dry gas, liquefied petroleum gas and gasoline. When the temperature of catalytic cracking is over 460 °C, the effects of thermal cracking must be considerable.     

Stratification of fuel for better engine performance

The concept of fuel stratification has been proposed and applied to a four-valve port injection spark ignition engine. In this engine, two different fuels or fuel components are admitted through two separate inlet ports and stratified into two regions laterally by strong tumble flows. Each stratified region has a spark plug to control the ignition. This engine can operate in the stratified lean-burn mode at part loads when fuel is supplied only to one of the inlet ports. While at high load operation, an improved fuel economy and higher power output are also expected through increased anti-knock features by taking advantage of the superior characteristics of different fuel or fuel components. This is achieved by igniting the lower RON (research octane number) fuel first and leaving the higher RON fuel in the end gas region. In this paper, knock limits of homogenous and different fuel stratification combustion modes at high loads were investigated experimentally. Primary reference fuels (PRF), iso-octane and n-heptane, were used to simulate three fuels of different RON: RON90, RON95 and RON100. The research results show that with stratified fuel components of low and high octane numbers, the knock limit, as defined by the minimum spark advance for knocking combustion, was extended apparently when the lower RON fuel was ignited first. In addition, the knock limit could also be extended by increasing the amount of higher RON fuel. However, igniting first the lower RON fuel in the fuel stratification combustion mode produced little improvement in anti-knock behaviour over the homogeneous combustion of the mixture of those two stratified fuels with an average RON.     

A 300 W laboratory reactor system for chemical-looping combustion with particle circulation

Chemical-looping combustion (CLC) is a method to burn gaseous fuels with inherent separation of carbon dioxide. A continuously operated laboratory reactor system for chemical-looping combustion with two interconnected fluidized beds was designed and built. This chemical-looping combustor was designed to operate with a fuel flow corresponding to 100–300 W. The CLC system was operated successfully using a highly reactive nickel-based oxygen-carrier. Furthermore, tests were carried out to determine the degree of gas leakage between the reactors. Although there was some leakage between the fuel and air reactors, it is low enough to enable evaluation of the combustion results. The combustion tests showed a high conversion of the natural gas to carbon dioxide, indicating that the particles are suitable for chemical-looping combustion. No methane was detected in the gas from the fuel reactor, and the fraction of carbon monoxide was in the range 0.5–3%.     

CARBON DIOXIDE STANDARD EMISSIVITY BY MIXED GRAY-GASES MODEL

Conventional fossil fuels are of carbon-hydrogen composition. A number of alternative fuels, e.g., coal, lignite, are carbon-based fuels. The high temperature combustion of such fuels would generate carbon dioxide, and if hydrogen is present, water vapor. The knowledge of the emissivities of carbon dioxide and water vapor is very important in burner design and thermal efficiency calculations. The present work utilizes a gray-plus-clear gas model to approximate standard carbon dioxide emissivities. The model developed covers a temperature range of 300-1800 K and a pL range of 0.05 to 1000 cm atm. The results indicated that a mixture of six gray gases was adequate to cover the whole range. Comparison of calculated and tabulated results showed that in the range of industrial application, the present model has an error range of —4.2 to 5.9 percent. Comparison with Leckner's model shows the superiority of the present work.     

CARBON DIOXIDE STANDARD EMISSIVITY BY MIXED GRAY-GASES MODEL

Conventional fossil fuels are of carbon-hydrogen composition. A number of alternative fuels, e.g., coal, lignite, are carbon-based fuels. The high temperature combustion of such fuels would generate carbon dioxide, and if hydrogen is present, water vapor. The knowledge of the emissivities of carbon dioxide and water vapor is very important in burner design and thermal efficiency calculations. The present work utilizes a gray-plus-clear gas model to approximate standard carbon dioxide emissivities. The model developed covers a temperature range of 300-1800 K and a pL range of 0.05 to 1000 cm atm. The results indicated that a mixture of six gray gases was adequate to cover the whole range. Comparison of calculated and tabulated results showed that in the range of industrial application, the present model has an error range of —4.2 to 5.9 percent. Comparison with Leckner's model shows the superiority of the present work.     

Development of an innovative 3-stage steady-bed gasifier for municipal solid waste and biomass

Gasification of biomass, municipal solid waste, waste-derived fuels and residues has been lately gaining in attractiveness as an alternative thermal treatment method to produce power and heat. Presented in this paper is a new, recently patented, 3-stage gasification scheme, designed for all aforementioned types of fuels and for producing a synthesis gas free of tar and dioxins. The proposed 3-stage gasification scheme comprises of three stages: i) pyrolysis, ii) combustion and iii) gasification. The proposed 3-stage gasification scheme is valid for municipal solid waste and any type of biomass despite differences in chemical composition. The innovation of this 3-stage gasification scheme is based on the fact that the transition between normal and reverse operation and vice versa is achieved only by the proper rotation settings of four air blowers, thus creating a new model of gaseous flow management between the three aforementioned stages. The presented model can achieve a safe industrial-scale operation while producing a gas free of harmful components. The proposed gasification model is validated as suitable for small-to-medium scale capacities, achieving an overall electrical efficiency of 30% and minimum environmental impacts well below all existing thresholds, including those set by the Directive 2000/76/EC on solid waste incineration.     

Prospects for the use of producer gas generated from fuels in the manufacture of steels

The inconsistency of the maximum temperature achieved in combustion (α = 1) of gaseous fuels and fuel oil with the problem of qualitatively heating steel products was demonstrated. The reasonability and method for the production of artificial gas from coal with various fixed heats of combustion for steel heating and electricity production were substantiated. A design for the combined (gas and then induction) heating of products was presented.     

Carbon gasification in the presence of metal catalysts

The development of new processes for the production of gaseous fuels from carbon-containing solids is essential in meeting the energy needs of the nation. In this paper, catalysed carbon gasification is examined. The change in the reactivity of the interface between gaseous reactant (hydrogen or steam) and solid carbon has been measured in the presence of various metal catalysts. With platinum it is found that over a range of temperatures the specific rate of methane production is of the same magnitude as the rate of hydrogen atomization. The catalytic effect is interpretable in terms of an enhanced rate of hydrogen dissociation on the metal surface, followed by surface diffusion across the metal/carbon interface and reaction with carbon. The gas formation rate during the interaction of water vapour with catalyst-activated carbons has been increased by more than an order of magnitude by depositing small weight fractions of active metal catalyst on the carbon surface. At the temperatures employed in this study (975–1175 K), carbon monoxide and hydrogen are the products of the catalysed reaction for each of the catalysts examined.     

A comparative experimental study of the autoignition characteristics of alternative and conventional jet fuel/oxidizer mixtures

Autoignition characteristics of an alternative (non-petroleum) and two conventional jet fuels are investigated and compared using a heated rapid compression machine. The alternative jet fuel studied is known as “S-8”, which is a hydrocarbon mixture rich in C₇-C₁₈ linear and branched alkanes and is produced by Syntroleum via the Fischer-Tropsch process using synthesis gas derived from natural gas. Specifically, ignition delay times for S-8/oxidizer mixtures are measured at compressed charge pressures corresponding to 7, 15, and 30 bar, in the low-to-intermediate temperature region ranging from 615 to 933 K, and for equivalence ratios varying from 0.43 to 2.29. For the conditions investigated for S-8, two-stage ignition response is observed. The negative temperature coefficient (NTC) behavior of the ignition delay time, typical of higher order hydrocarbons, is also noted. Further, the dependences of both the first-stage and the overall ignition delays on parameters such as pressure, temperature, and mixture composition are reported. A comparison between the autoignition responses obtained using S-8 and two petroleum-derived jet fuels, Jet-A and JP-8, is also conducted to establish an understanding of the relative reactivity of the three jet fuels. It is found that under the same operating conditions, while the three jet fuels share the common features of two-stage ignition characteristics and a NTC trend for ignition delays over a similar temperature range, S-8 has the shortest overall ignition delay times, followed by Jet-A and JP-8. The difference in ignition propensity signifies the effect of fuel composition and structure on autoignition characteristics.     

Safe operating conditions determination for stationary SI gas engines

Knock is a major problem when running combined heat and power (CHP) gas engines because of the variation in the network natural gas composition. A curative solution is widely applied, using an accelerometer to detect knock when it occurs. The engine load is then reduced until knock disappears. The present paper deals with a knock preventive device. It is based on the knock prediction following the engine operating conditions and the fuel gas methane number, and it acts on the engine load before knock happens. A state of the art about knock prediction models is carried out. The maximum of the knock criterion is selected as knock risk estimator, and a limit value above which knock may occur is defined. The estimator is calculated using a two-zone thermodynamic model. This model is specifically based on existing formulas for the calculation of the combustion progress, modified to integrate the effect of the methane number. A chemical kinetic model with 53 species and 325 equilibrium reactions is used to calculate unburned and burned gases composition. The different parameters of the model are fitted with a least squares method from an experimental data base. Errors less than 8% are achieved. The knock risks predicted for various natural gases and operating conditions are in agreement with previous work. Nevertheless, the knock risk estimator is overestimated for natural gases with high concentrations of inert gases such as nitrogen and carbon dioxide. The definition of a methane number limit based on the engine manufacturer's recommendation is then required to eliminate unwarranted alerts. Safe operating conditions are thus calculated and gathered in the form of a map. This map, combined with the real time measurement of the fuel gas methane number, can be integrated to the control device of the CHP engine in order to guarantee a safe running towards fuel gas quality variation.     

Decomposition of polyethylene in radio-frequency nitrogen and water steam plasmas under reduced pressures

The possibility of radio-frequency (RF) nitrogen and water steam plasmas under reduced pressures for gasification of plastic waste as a thermal recycling method has been investigated in order to develop an innovative method for directly recycling plastic waste to hydrogen, synthesis gases or fuels. The products of pyrolysis were analyzed and classified into gaseous fraction and solid soot; and analytical interest was focused on the gaseous product composition. It was found that the electrode geometry, input power, reactor pressure and plasma working gas were the key parameters affecting the plasma characteristics and pyrolysis product. Experiments with different plasma media indicated that when polyethylene (PE) powder was injected into nitrogen plasma, the PE was decomposed and hydrogen formed as a main product by reaction with the plasma; when water steam plasma was used for conversion of PE, the carbon conversion to gas was dramatically enhanced in the presence of water steam, and the main gas products were carbon monoxide and hydrogen. Preliminary solid products analysis and pyrolysis mechanisms for the different plasmas processes were also discussed.     

Catalytic Partial Oxidation. Part I. Catalytic Processes to Convert Methane: Partial or Total Oxidation

The presence of large reserves of natural gas has stimulated research to utilize methane, its principal component, as an alternative energy source and to convert it to other fuels and industrially important chemicals. The reserves of natural gas in the world are estimated to be 1.4 × 10¹⁴ Nm³, while new gas fields are being discovered every year. Although this natural gas is available under pressure for piping and transport, extensive research efforts have been directed to develop gas-to-liquid (GTL) technology for the conversion of remote natural gas reserves into high-added-value liquid products, such as methanol and synthetic fuels, that can be more easily transported. A further incentive for natural gas utilization originates from environmental concerns that drive the search for cleaner energy sources. Catalytic combustion of methane offers an attractive alternative to gas-phase homogeneous combustion since it can stabilize flames at lower fuel-to-air ratios, thereby lowering flame temperatures and reducing NO_x emission. Another alternative can be found in the conversion of natural gas into hydrogen, which can be used to generate electricity in fuel cells. Fuel cells have a much higher energy efficiency compared to current combustion-based power plants. Also, hydrogen is a much cleaner fuel than hydrocarbon feedstocks since the only product from hydrogen fuel cells is water.     

Experimental investigation on dual fuel operation of acetylene in a DI diesel engine

Depletion of fossils fuels and environmental degradation have prompted researchers throughout the world to search for a suitable alternative fuel for diesel engine. One such step is to utilize renewable fuels in diesel engines by partial or total replacement of diesel in dual fuel mode. In this study, acetylene gas has been considered as an alternative fuel for compression ignition engine, which has excellent combustion properties.Investigation has been carried out on a single cylinder, air cooled, direct injection (DI), compression ignition engine designed to develop the rated power output of 4.4 kW at 1500 rpm under variable load conditions, run on dual fuel mode with diesel as injected primary fuel and acetylene inducted as secondary gaseous fuel at various flow rates. Acetylene aspiration resulted in lower thermal efficiency. Smoke, HC and CO emissions reduced, when compared with baseline diesel operation. With acetylene induction, due to high combustion rates, NO_x emission significantly increased. Peak pressure and maximum rate of pressure rise also increased in the dual fuel mode of operation due to higher flame speed. It is concluded that induction of acetylene can significantly reduce smoke, CO and HC emissions with a small penalty on efficiency.     

Reaction Kinetics and Coking Behavior for Furan Deoxygenation via Catalytic Pyrolysis Using Methane

The effective deoxygenation of oxygenates remains a major challenge that needs to be overcome for industrial‐scale conversion of biomass to fuels. Present technology uses expensive gaseous hydrogen for deoxygenation. This work looks at the possibility of using methane or natural gas as an alternative for the deoxygenation process. Catalytic pyrolysis studies were carried out using furan as the model oxygenate in the presence of methane in a fixed‐bed reactor over 5 % Ni/HZSM‐5 as catalyst. The effects of temperature and space velocity on the catalyst activity, reaction kinetics, and deactivation behavior were studied. It was found that the deoxygenation of furan was first and second order with respect to furan and methane concentration, respectively. Deactivation studies suggested that catalyst deactivation takes place through poisoning, fouling, and sintering.     

Rich-Catalytic Lean-burn combustion for fuel-flexible operation with ultra low emissions

A Rich-Catalytic Lean-burn (RCL^®) combustion system was developed for operation on natural gas, but also provides significant advantages for fuel-flexible operation on non-methane fuels. Most notably, fuel-rich operation limits the extent of catalyst-stage reaction based on available oxygen, regardless of the fuel's intrinsic reactivity on the catalyst. Thus, similar catalyst and reactor performance can be obtained for widely varying fuel types.

In addition, catalytic pre-reaction extends the combustor's lean flammability limit for all fuels, allowing low-temperature combustion of both conventional and low-heating-value fuels, with concomitant low NO_x emissions.

This paper presents test results for RCL^® combustion with various fuel types, including gaseous, pre-vaporized liquid, and simulated low-Btu fuels. Although these fuels have widely varying properties, a single type of catalytic reactor was successfully tested for all of these fuels by modifying only the fuel delivery system upstream of the reactor. Test results show similar reactor performance for all fuels tested.     

A diffusion-kinetic model for pulverized-coal combustion and heat-and-mass transfer in a gas stream

A diffusion-kinetic model for pulverized-coal combustion and heat-and-mass transfer in a gas stream is proposed, and the results of numerical simulation of the burnout dynamics of Kansk-Achinsk coals in the pulverized state at different treatment conditions and different model parameters are presented. The mathematical model describes the dynamics of thermochemical conversion of solid organic fuels with allowance for complex physicochemical phenomena of heat-and-mass exchange between coal particles and the gaseous environment.     

Kinetic relationship of coal hydrogenation,pyrolysis and dissolution

Data are presented concerning the production of gaseous and liquid products from coal. The processes considered include pyrolysis, dissolution in solvent with and without the application of ultrasonic energy, batch hydrogenation, and continuous hydrogenation. The products are compared with respect to both quantity and type. Activation energies are presented and mechanisms discussed. Coal hydrogenation in the presence of an appropriate catalyst shows very great promise as a means of converting coal to liquid and gaseous fuels. Yields of 30% high octane gasoline, 5% diesel oil, 35% high Btu gas, and 30% char, on a weight basis, have been achieved.