Search Results

A 3D-CFD model with detailed chemical kinetics was developed to investigate the combustion characteristics of HCCI engines, especially those fueled with hydrogen and n-heptane. The effects of changes in some of the key important variables that included compression ratio and chamber surface temperature on the combustion processes were investigated. Particular attention was given, while using a finer 3-D mesh, to the development of combustion within the chamber crevices between the piston top-land and cylinder wall. It is shown that changes in the combustion chamber wall surface temperature values influence greatly the autoignition timing and location of its first occurrence within the chamber. With high chamber wall temperatures, autoignition takes place first at regions near the cylinder wall while with low surface temperatures; autoignition takes place closer to the central region of the mixture charge.

A hydrogen economy is an increasingly popular solution to lower global carbon dioxide emissions. Previous research has been focused on the economic conditions necessary for hydrogen to be cost competitive, which tends to neglect the effectiveness of greenhouse gas mitigation for the very solutions proposed. The holistic carbon footprint assessment of hydrogen production, distribution, and utilization methods, otherwise known as “well-to-wheels” carbon intensity, is critical to ensure the new hydrogen strategies proposed are effective in reducing global carbon emissions. When looking at these total carbon intensities, however, there is no single clear consensus regarding the pathway forward. When comparing the two fundamental technologies of steam methane reforming and electrolysis, there are different scenarios where either technology has a “greener” outcome.

CO/H2 (ratios i.e. water gas shift equilibria) in exhaust gases produced from the combustion of pure isooctane, methanol, and methane in a pulse flame combustor were measured. Measured CO/H2 ratios were directionally consistent with C/H ratios of the respective fuels. The average CO/H2 ratios in combusted isooctane, methanol, and methane were found to be 3.8, 1.25, and 2.0, respectively. The effect of these differences on feedback A/F control with a HEGO (heated exhaust gas oxygen) sensor were also examined. Feedback control of isooctane combustion produced operation very near to stoichiometry. On the other hand, the combustion of methanol under feedback control resulted in steady state lean operation while feedback control of methane combustion produced rich operation. For all three fuels, operation shifted in the lean direction as combustion efficiency was degraded.

The combustion processes of of lean mixtures of methane in air is examined by employing a detailed chemical kinetic scheme consisting of 178 elementary reaction steps with 41 species. The changes with time in the concentrations of the major relevant reactive species are determined from the preignition reactions to the time near equilibrium conditions. The results of such an approach to the combustion process are considered over a wide range of initial temperatures (1000 K - 1600 K) and equivalence ratios (0.2 - 1.2) while the pressure was kept at atmospheric. Calculated results obtained while using this model tend to be in good agreement with the corresponding experimental values of ignition delay. The ignition delay of methane-air mixture correlated by the following empirical expression in which constants A and B are function of the equivalence ratio while Ti is the initial mixture temperature in °K.

It is well known the dual fuel operation at lower loads suffers from lower thermal efficiency and higher unburned percentages of fuel. The present work includes a computational investigation to predict the effects of Exhaust gas recirculation (EGR) on the operation of an indirect-injection dual fuel (Ricardo-E6) engine by using a detailed chemical kinetic scheme and a quasi-two zone analytical model. The comprehensive chemical kinetic scheme for methane oxidation consisting of 178 elementary reaction steps with 41 species. A quasi-two zone analytical model is based on the effective energy releases of the pilot diesel fuel while using the detailed chemical reaction kinetic scheme for the oxidation of methane. Through the results, it was shown that, the active species such as H, O and OH produced in the high temperature combustion process and found in the exhaust gases are play a significant role in the preignition reactions.

In this work, the spark-ignition (SI) of a methane/air mixture contained in a constant-volume chamber is investigated by numerical simulations. A cylinder-shaped vessel filled with a methane/air mixture containing two electrodes is used as simulation model. The impact of an electrical discharge at the electrodes on the surrounding gas is simulated, with detailed treatment of the ignition process involvig chemical kinetics, transport phenomena in the gas-phase and electrodynamical modeling of the interaction between spark and fuel/air mixture. For the calculations, a 2D-code to simulate the early stages of flame development, shortly after the breakdown discharge, has been developed. Computational results are shown for ignition of a methane air-mixture.

Investigations have concluded that methane does not appear to be photochemically reactive in the atmospheric system and does not participate in smog formation. Since methane is “nonreactive,” and may in the future be excluded from the total unburned hydrocarbon emissions, an instrument was designed and developed (termed the “methane analytical system”) enabling methane emissions to be quantified separately from total unburned hydrocarbon emissions. The instrument employed gas chromatographic principles whereby a molecular sieve column operating isothermally separated methane from the nonmethane hydrocarbons. Direct on-line sampling occurred via constant volume sample loops. The effluent was monitored with a flame ionization detector. The instrument was fully calibrated (i.e., extremely linear response over a large concentration range) for use with Diesel engines as part of an ongoing alternative fuels research program.

A special combustion chamber is described which burns a small, representative, fraction of the intake mixture of natural-gas-fuelled spark-ignition engines. The combustion end products are led to a lambda sensor which, consequently, will not be deteriorated by lubricating-oil additives and will not be hampered in its operation by unburnt methane. That leads to a largely extended life of the lambda sensor. The paper discusses the construction and control of the special chamber and ends with a discussion on the representativeness of the measured oxygen concentration for the air-to-fuel ratio.

Dual-fuel diesel-natural gas (NG) engine exhibits higher power density and lower specific emissions compared to dedicated diesel engines. However, high intake temperatures, high compression ratios, combined with high engine loads may lead to engine knock. This is potentially a limiting factor on engine downsizing and getting higher power. In the present study, the combustion process under knocking conditions has been investigated in a dual-fuel diesel-NG engine. A comprehensive multi-dimensional simulation framework was generated by integrating the CHEMKIN chemistry solver into the KIVA-3V code. A detailed chemical kinetics mechanism was used for n-heptane and methane as diesel and NG surrogates. Combination of detailed chemical kinetics and detailed fluid dynamics calculation enabled the model to take into account the characteristics of most pronounced knock type in dual-fuel engines, so called end-gas knock.

The use of hydrogen as a fuel supplement for lean-burn engines at higher compression ratios has been studied extensively in recent years, with good promise of performance and efficiency gains. With the advances in reformer technology, the use of a gaseous fuel stock, comprising of substantially higher fractions of hydrogen and other flammable reformate species, could provide additional improvements. This paper presents the performance and emission characteristics of a gas mixture of equal volumes of hydrogen, CO, and methane. It has recently been reported that this gas mixture can be produced by reforming of ethanol at comparatively low temperature, around 300C. Experiments were performed on a 1.8-liter passenger-car Nissan engine modified for single-cylinder operation. Special pistons were made so that compression ratios ranging from CR= 9.5 to 17 could be used. The lean limit was extended beyond twice stoichiometric (up to lambda=2.2).

Bioregenerative systems for removal of gaseous contaminants are desired for long-term space missions to reduce the equivalent system mass of the air cleaning system. This paper describes an innovative design of a new biofiltration test lab for investigating the capability of biofiltration process for removal of ersatz multi-component gaseous streams representative of spacecraft contaminants released during long-term space travel. The lab setup allows a total of 24 bioreactors to receive identical inlet waste streams at stable contaminant concentrations via use of permeations ovens, needle valves, precision orifices, etc. A unique set of hardware including a Fourier Transform Infrared (FTIR) spectrometer, and a data acquisition and control system using LabVIEW™ software allows automatic, continuous, and real-time gas monitoring and data collection for the 24 bioreactors. This lab setup allows powerful factorial experimental design.

The objective of this paper is to introduce a new method for full-field measurement of local average gas-phase fuel concentration in a transient axisymmetrical gas-jet or evaporating spray. Since the combustion process in a diesel engine is a diffusion flame, the local fuel concentration as a function of time is one of the factors that governs engine efficiency and emissions. The method is utilizing the classic Schlieren technique. A CCD camera and frame-grabber combination is used to record the data. Based on these data and the assumption that the flow-field is axisymmetrical, the local index of light refraction is calculated, and from this an estimate of the local gas-phase fuel concentration is made. Since the flow-field is turbulent, data from a large number of separate injections are used. Therefore the results should represent the development of the average flow-field. Since it is a full-field method, the results can be checked for overall conservation of mass.

To elucidate the complex characteristics of pre-chamber combustion engines, the interaction of the hot gas jets initiated by an active narrow throated pre-chamber with lean premixed CH4/air in a heavy-duty engine was studied computationally. A twelve-hole KAUST proprietary pre-chamber geometry was investigated using CONVERGE software. The KAUST pre-chamber has an upper conical part with the spark plug, and fuel injector, followed by a straight narrow region called the throat and nozzles connecting the chambers. The simulations were run for an entire cycle, starting at the previous cycle's exhaust valve opening (EVO). The SAGE combustion model was used with the chemistry modeled using a reduced methane oxidation mechanism based on GRI Mech 3.0, which was validated against in-house OH chemiluminescence data from the optical engine experiments.

The spark-ignited pre-chamber stratified combustion system is one of the most effective ways of expanding lean-burn ability and improving the performance of a natural gas engine. For these pre-chamber engines, the geometrical structure of orifices between the pre- and main chamber plays a significant role on the gas flow and flame propagation behaviors. The present study aims to investigate the effects of orifice number and diameter on combustion characteristics of a Shengdong T190 natural gas engine through CFD simulation. Various geometrical structures for the pre-chamber orifices were designed, offering variations in the number of orifices (4 to 8), and in the diameter of orifices (1.6mm to 2.9mm). A non-dimensional parameter β was employed to characterize the relative flow area of the orifices in the design. CFD simulations of combustion processes for these designs were carried out using a simplified chemical reaction kinetic mechanism for methane.

The present contribution combines the consideration of the chemical reaction activity of the end gas and engine operating conditions to predict the onset of knock and associated performance in a spark ignition engine fuelled with methane. A two-zone predictive combustion model was developed based on an estimate of the effective duration of the combustion period and the mass burning rate for any set of operating conditions. The unburned end gas preignition chemical reaction activity is described by a detailed chemical reaction kinetic scheme for methane and air. The variation with time of the value of a formulated dimensionless knock parameter based on the value of the cumulative energy released due to preignition reaction activity of the end gas per unit volume relative to the total energy release per unit cylinder swept volume is calculated It is shown that whenever knocking is encountered, the value of builds up to a sufficiently high value that exceeds a critical value.

The present study extends our previous methane flame chemistry to methane autoignition based on most recent shock-tube experiments. It results in a detailed mechanism that consists of 128 elementary reactions among 31 species and that can be applied to predicting methane autoinginition times for temperatures between 1000 K and 2000 K, pressures between 1 bar and 250 bar and equivalence ratios between 0.4 and 3. A 9-step short mechanism is derived from this detailed mechanism with the objective of predicting knock in dual-fuel engines for equivalence ratio between 0.5 and 1.5 with temperature ranging 800 to 1200 K and pressure from 50 to 150 bar.

The diesel/natural gas engine configuration provides a potential alternative solution for PM and NOx emissions reduction from typical diesel engine operations. However, their engine operations suffer from high NMHC/methane emissions and poor engine performance, especially at light loads. By increasing the diesel pilot quantity, the performance and reduction of NMHC/methane emissions can be improved but the emission levels are still very high. Clearly, a typical DOC is not good enough to treat NMHC/methane emissions. Methane has been known as one of most stable species that is difficult to catalytically oxidize in lean burn environment and low exhaust temperatures. An aftertreatment system exclusively designed for treating methane emissions from DDF operations is therefore necessary. The current work is aimed to establish an effective computational tool in order to study the newly proposed catalytic converter system concept on treating methane from DDF operations.

Research has been conducted on Controlled Auto-Ignition (CAI) engine with natural gas. CAI engine has the potential to be highly efficient and to produce low emissions. CAI engine is potentially applicable to automobile engine. However due to narrow operating range, CAI engine for automobile engine which require various speed and load in real world operation is still remaining at research level. In comparison some natural gas engines for electricity generation only require continuous operation at constant load. There is possibility of efficiency enhancement by CAI combustion which is running same speed at constant load. Since natural gas is primary consisting of methane (CH4), high auto-ignition temperature is required to occur stable auto-ignition. Usually additional intake heat required to keep stable auto-ignition. To keep high compression temperature, single cylinder natural gas engine with high compression ratio (CR=26) was constructed.

The combustion characteristics of three gaseous fuels (hydrogen, methane and ethane) in a direct-injection stratified-charge single-cylinder engine with a centered square head-cup operated at 800 rpm (compression ratio = 10.8, squish ratio = 75%, nominal swirl ratio = 4) were studied to assess the extent to which the combustion is controlled by turbulent mixing, laminar mixing and chemical kinetics. The injection of gaseous fuels was via a Ford AFI injector, originally designed for the air-forced injection of liquid fuel. Pressure measurements in the engine cylinder and in the injector body, coupled with optical measurements of the injector poppet lift and shadowgraph images of the fuel jets provided both quantitative and qualitative information about the in-cylinder processes. To make the cases comparable, the total momentum of the fuel jets and the total heat released by the three fuels was kept the same (equivalence ratio = 0.316, 0.363, 0.329 for H2, CH4 and C2H6, respectively).

Issues that must be addressed to make Homogeneous Charge Compression Ignition (HCCI) engines a practical reality include the difficulty of controlling the ignition timing and suppression of rapid combustion under high load conditions. Overcoming these issues to make HCCI engines viable for practical application is indispensable to the further advancement of internal combustion engines. Previous studies have reported that the operating region of HCCI combustion can be expanded by using DME and Methane blended fuels.(1), (2), (3), (4), (5) The reason is that the reaction characteristics of these two low-carbon fuels, which have different ignition properties, have the effect of inducing heat release in two stages during main combustion, thus avoiding excessively rapid combustion. However, further moderation of rapid combustion in high-load region is needed to expand the operation region. This study focused on supercharging and use of blended fuels.