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The CO2 capture performance of sorbents derived from three distinct limestones, including a metamorphosed limestone, is studied under conditions relevant for calcium looping CO2 capture from power plant flue gas. The combined and individual influence of flue gas H2O and SO2 content, the influence of textural changes caused by sequential calcination/carbonation cycles, and the impact of CaSO4 accumulation on the sorbents' capture performance were examined using bubbling fluidized bed reactor systems. The metamorphosed limestone-derived sorbents exhibit atypical capture behavior: flue gas H2O negatively influences CO2 capture performance, while limited sulfation can positively influence CO2 capture, with space time significantly impacting CO2 and SO2 co-capture performance. The morphological characteristics influencing sorbents' capture behavior were examined using imaging and material characterization tools, and a detailed discussion is presented. This insight into the morphology responsible for metamorphosed limestone-derived sorbent's anomalous capture behavior can guide future sorbent selection and design efforts.

This work was conducted with the help of several people. Adrian Ichim helped in setting up the engine and solving issues related to the engine. iAV provided a new module to run two separate pumps simultaneously that allowed direct injection of two fluids in the cylinder. The authors would like to thank Saudi Aramco for funding the project under the aegis of FuelCom II.

Fuel injection strategies often have a considerable impact on pre-ignition in high specific output gasoline engines. Splitting the injection event into two or more pulses has been widely explored as one means of reducing pre-ignition. As effective as these strategies can be with respect to pre-ignition suppression, they often introduce other compromises into the combustion process, for example, reduced indicated mean effective pressure or greater cycle-to-cycle variation. This study examines a split injection strategy with up to three injection pulses for suppressing pre-ignition, while optimizing the start of injection and duration of injection to minimize the associated compromises on the combustion process. The results demonstrate that splitting the injection event generally lowers the in-cylinder temperature and reduces the fuel mass that reaches the cylinder liner. This leads to a lower probability of creating oil-fuel droplets, which may act as a precursor for pre-ignition. The split injection strategy with a late injection when the piston is close to top dead center is shown to perform even better in terms of pre-ignition suppression, while providing comparable indicated mean effective pressure and cycle-to-cycle variation to the baseline case with a single injection pulse. Finally, the injection pressure is varied to establish an optimal combination of operating parameters for avoiding pre-ignition in high specific output gasoline engines.

Ion current sensing has the potential to become a promising combustion diagnostic technique for mass productive engines. In this paper, the effect of electric fields on ion current signals measured from a series of methane/air flames in a constant volume combustion chamber (CVCC) is investigated both experimentally and numerically. Based on simultaneous flame Schlieren imaging and ion current measurement, the relation between the flame/electrodes contact area and the ion current signal waveform is explored under different electric field configurations. A CFD model, which incorporates flame plasma hydrodynamics, neutral/charged species reaction kinetics and ion-electric field interactions, is constructed. The effect of the electric field on the ion distribution and the charged species flux are analyzed, and the signal amplitude and timing are well predicted under the equivalence ratio range of Ф = 0.7–1.1. Besides, the behavior of electrons, which is normally neglected in previous studies, is also analyzed in this work. The results show that it will affect the signal as well. The electron produced in the flame front zone can hardly diffuse into the pre-flame zone (

International audience; Formic acid is a promising fuel candidate that can be generated by reacting renewable hydrogen with carbon dioxide. However, the burning characteristics of formic acid/air mixtures have not been extensively studied. Furthermore, due to its low reactivity, the addition of hydrogen to formic acid/air mixtures may help with improving burning characteristics. This paper presents the first extensive study of formic acid/air premixed laminar burning velocities, as well as mixtures with hydrogen and carbon dioxide. Unstretched laminar burning velocities and Markstein lengths of formic acid in air for two different unburnt gas temperatures and equivalence ratios are presented. Measurements of formic acid mixed with various proportions of hydrogen and carbon dioxide in air are also studied as a potential renewable fuel for the future. Experimental results demonstrate the low burning velocities of formic acid, and the ability to significantly enhance flame speeds by hydrogen addition. A modified detailed kinetic model for combustion of formic acid and its mixtures with hydrogen is proposed by merging well-validated literature models. The proposed model reproduces the experimental observations and provided the basis for understanding the combustion kinetics of formic acid laminar premixed flames, as well as mixtures with hydrogen. It is shown that the HOCO radical is the principal intermediate in formic acid combustion, and hydrogen addition accelerates the decomposition of HOCO radical thereby accelerating burning velocities.

The downsizing and boosting of automotive engines for increased fuel economy poses challenges in both obtaining stable ignition at boosted intake pressures and high dilution conditions. Pulsed nano...

The use of a spark plug ion sensor to detect combustion timing in a homogeneous charge compression ignition (HCCI) engine is a technique that could alleviate the need for pressure transducers, a more expensive alternative. One disadvantage of this approach is the difficulty in obtaining a strong signal at lower equivalence ratios. This article addresses and compares three ion sensing circuitries, namely a voltage follower, a notch filter circuit that removes the 60-Hz wall noise, and a notch filter whose output is coupled to a custom-built “integrator” circuit. The circuit optimizations are aimed at improving signal strength and reliability. The ion signal present in the combustion chamber is experimentally investigated in a 1.9-L Volkswagen engine, modified for HCCI operation and fueled with gasoline. Experiments are conducted across different intake temperatures, pressures, and equivalence ratios. It was found that the custom-built circuit provided the best ion signal strength and reliability.

Gasoline Compression Ignition (GCI) is a promising engine operating mode that can reduce maximum pressure rise rate (MPRR) without knock tendency and better control the combustion phasing compared to the Homogeneous Charge Compression Ignition (HCCI) by using a late direct-injection (DI). In this study, a 107-species reduced mechanism and a 207-species skeletal mechanism were developed using the Computer Assisted Reduction Mechanism (CARM) and validated under engine conditions for a newly developed 5-component surrogate for a Haltermann 437 certification gasoline (AKI = 93). Then, 3D computational fluid dynamics (CFD) simulations with an optimized grid size determined by a grid convergence study were performed with the 107-species reduced mechanism and the 5-component certification gasoline surrogate. Two experimental boosted GCI cases with similar, moderate MPRR and heat release parameters, but different second DI timings (−52° aTDC and −5° aTDC), were validated and analyzed. For the −52° aTDC DI case, the combustion can be interpreted as a partially sequential auto-ignition due to the competition between the charge cooling effect and the equivalence ratio (ϕ)-sensitive effect of the stratified mixture, which is responsible for mitigating the MPRR. For the −5° aTDC DI case, the combustion can be decoupled into a partially sequential auto-ignition and a subsequent non-premixed combustion by the DI fuel near top dead center in the compression stroke. The MPRR is relaxed through the slow, mixing-limited combustion between the injected fuel and the premixed mixture.

Modes of reaction front propagation and end-gas combustion of hydrogen/air mixtures in a closed chamber are numerically investigated using an 1-D unsteady, shock-capturing, compressible and reacting flow solver. Different combinations of reaction front propagation and end-gas combustion modes are observed, i.e., 1) deflagration without end-gas combustion, 2) deflagration to end-gas autoignition, 3) deflagration to end-gas detonation, 4) developing or developed detonation, occurring in the sequence of increasing initial temperatures. Effects of ignition location and chamber size are evaluated: the asymmetric ignition is found to promote the reactivity of unburnt mixture compared to ignitions at center/wall, due to additional heating from asymmetric pressure waves. End-gas combustion occurs earlier in smaller chambers, where end-gas temperature rise due to compression heating from the deflagration is faster. According to the ξ−e regime diagram based on Zeldovich theory, modes of reaction front propagation are primarily determined by reactivity gradients introduced by initial ignition, while modes of end-gas combustion are influenced by the total amount of unburnt mixture at the time when autoignition occurs. A transient reactivity gradient method is provided and able to capture the occurrence of detonation.

This study investigates the effect of using terpineol as an octane booster for gasoline fuel. Unlike ethanol, terpineol is a high energy density biofuel that is unlikely to result in increased volumetric fuel consumption when used in engines. In this study, terpineol is added to non-oxygenated FACE F gasoline (Research Octane Number = 94.5) in volumetric proportions of 10%, 20% and 30% and tested in a single cylinder spark ignited engine. The performance of terpineol blended fuels are compared against a standard oxygenated EURO V (ethanol blended) gasoline. It was determined that the addition of terpineol to FACE F gasoline enhanced the octane number of the blend, resulting in improved brake thermal efficiency and total fuel consumption. For FACE F + 30% terpineol, break thermal efficiency was improved by 12.1% over FACE F gasoline at full load for maximum brake torque operating point, and similar performance as EURO V gasoline was achieved. Due to its high energy density, total fuel consumption was reduced by 6.2% and 9.7% with 30% terpineol in the blend when compared to FACE F gasoline at low and full load conditions, respectively. Gaseous emissions such as total hydrocarbon and carbon monoxide emission were reduced by 36.8% and 22.7% for FACE F + 30% terpineol compared to FACE F gasoline at full load condition. On the other hand, nitrogen oxide and soot emissions are increased for terpineol blended FACE F gasoline when compared to FACE F and EURO V gasoline.

The pre-ignition is very challenging for modern gasoline engines with high pressure boost and gasoline direct injection (GDI) system. Except optical imaging method, effective pre-ignition diagnostic methods are very limited. This paper presents the recent research in the feasibility of using ion current for pre-ignition diagnosis. In agreement with the theory of the ion current based pre-ignition diagnosis, this paper summarizes the simulation studies of the ionization process using chemical kinetics under the equivalent pre-ignition conditions. The simulations are conducted under both constrained boundary conditions and shockwave compressed conditions. The research results indicate that the equivalence ratio of active ionization is in the range of ‘0.8’–‘1.6’. The pressure has insignificant influence on the reaction rate of ionization in low temperature (

Improving the octane number of gasoline offers the potential of improved engine combustion, as it permits spark timing advancement without engine knock. This study proposes the use of terpineol as an octane booster for gasoline in a spark ignited (SI) engine. Terpineol is a bio-derived oxygenated fuel obtained from pine tree resin, and has the advantage of higher calorific value than ethanol. The ignition delay time (IDT) of terpineol was first investigated in an ignition quality tester (IQT). The IQT results demonstrated a long ignition delay of 24.7 ms for terpineol and an estimated research octane number (RON) of 104, which was higher than commercial European (Euro V) gasoline. The octane boosting potential of terpineol was further investigated by blending it with a non-oxygenated gasoline (FACE F), which has a RON (94) lower than Euro V gasoline (RON = 97). The operation of a gasoline direct injection (GDI) SI engine fueled with terpineol-blended FACE F gasoline enabled spark timing advancement and improved engine combustion. The knock intensity of FACE F + 30% terpineol was lower than FACE F gasoline at both maximum brake torque (MBT) and knock limited spark advance (KLSA) operating points. Increasing proportions of terpineol in the blend caused peak heat release rate, in-cylinder pressure, CA50, and combustion duration to be closer to those of Euro V gasoline. Furthermore, FACE F + 30% terpineol displayed improved combustion characteristics when compared to Euro V gasoline.

Ion current sensing technology has the potential to be a low cost and real time combustion phasing solution for HCCI or HCCI-like engine control. Based on a primary reference fuel oxidation mechanism and a C1–C4 hydrocarbon flame ionization mechanism, a skeletal mechanism for gasoline flame ionization process prediction on HCCI engines was developed in this paper. Since the ion concentrations significantly affect the aroused ion current signals, the mechanism is targeted on accurately predicting both the ion production concentrations and other key combustion characteristics. Through the comparison with the results from the detailed gasoline flame ionization mechanism and experimental results, the predicted maximum hydronium (H3O+) ion concentration and the concentration variation tendency are validated. Additionally, the auto-ignition delay time (tign) accurately predicted under HCCI engine conditions. Through coupling with a 3D-CFD engine model, the skeletal mechanism was applied to predict the important information of in-cylinder ion species, which are validated by the experimental ion current amplitudes and phases. The results show that the ion current phase (Ion50) matches well with the positions where the predicted ion concentration reaches its maximum, and the ion current amplitudes are well predicted under the conditions of different equivalence ratios (Φ) and fuel injection ratios (Injratio).

Advanced combustion engine (ACE) research is typically carried out on single-cylinder research engines. These engines are designed to tightly control fueling and conditions at intake valve closure (IVC) and to precisely measure in-cylinder conditions and emissions. However, to be able to measure and control engine operation so precisely, these research engines typically do not feature intake and exhaust tracts that resemble those in production engines, specifically in regards to turbomachinery, heat exchangers, and exhaust gas recirculation (EGR) systems. For this reason, these research engines are effective for understanding in-cylinder combustion parameters such as heat release rate, burn duration, combustion efficiency, pollutant formation, and exhaust valve opening (EVO) conditions. This paper applies high fidelity simulations to determine the feasibility of achieving a chosen single cylinder engine operating point on a production type homogeneous charge compression ignition (HCCI) engine, using a partial fuel stratification (PFS) strategy. To accomplish this, a Converge 3 dimensional (3D) – computational fluid dynamics (CFD) model of the experimental combustion chamber and intake and exhaust runners was created to simulate the experimental engine. This model was used to simulate an operating point achieved experimentally, as well as to determine the sensitivity of the operating point to variations in intake pressure, intake temperature, injection timing, injected mass, and EGR fraction. The results from these simulations were fed into a 1-dimensional engine simulation created in AVL Boost, featuring production-type intake and exhaust systems, including turbomachinery and heat exchangers necessary to create the required IVC conditions. This full engine simulation was used to assess the cycle efficiency of the engine at the experimental operating condition, and to assess whether changes to this operating point in intake temperature, intake pressure, direct injection timing, or fueling are beneficial to the cycle efficiency and engine-out emissions. In addition, the sensitivity of promising engine operating points to injection timing and injection mass are determined to evaluate the potential stability of these operating points.

Turbulent lifted flames of diesel–propane blend fuels issuing into a vitiated co-flow are recorded with a high-speed camera. The spray characteristics, flame structures, ignition delays, and lift-off heights of jet flames of diesel–propane blend fuels are analyzed in this research. As an additive to diesel fuel, propane has little influence on the autoignition process of diesel from the perspective of chemical kinetics but it improves the atomization, evaporation, and turbulence of the fuel spray. The addition of propane is beneficial for studying the interaction of the chemical kinetics and fluid dynamics in turbulent lifted flames. The experimental results show that the propane fraction has different influences on the ignition delay in two temperature ranges. The ignition delay increases with the increase of the fraction of propane when the co-flow temperature is lower than 1080 K and decreases when the co-flow temperature is higher than 1117 K. Thus, a related mechanism controlling the ignition delay o...

As an approach to replace pressure transducers, ion current sensing is a promising candidate for overcoming the difficult task of controlling the start of combustion in Homogeneous Charge Compression Ignition (HCCI) engines which require feedback from previous cycles. In this study, cyclic variations and prior-cycle effects of ion current signals are analyzed by comparing against pressure transducer signals using time-series methods in an HCCI engine. Additionally, the effects of various calibrated ion signal intensities are tested by adding cesium acetate (CsOAc) to the base fuel. Nonlinear characteristics of ion current signals are identified to cause strong cyclic variations through a single-zone model analysis with different equivalence ratios. By analyzing the time series, return maps, and coefficient of variations (CoV), the study finds that the stability of the ion signals can be largely improved by adding CsOAc due to the low ionization energy. After reconstructing a complex, nonlinear dynamical system model with symbol-sequence statistics, the measured cycle-resolved data of the ion current signal is analyzed to determine the pattern structures within prior cycles of fixed length, which is optimized by a modified Shannon entropy calculation. The results suggest that long, consecutive symbols of the ion current signal can be reliably predicted through the application of designed deterministic patterns especially when a small amount of CsOAc is added, although the ion current signal is normally considered a localized information provider and affected by many dynamical factors. Consequently, ion current signals are very promising for model-based control systems in HCCI engines with tolerable amounts of signal enhancing additives.

A sparkplug ion sensor can be used to measure the ion current in a homogeneous charge compression ignition (HCCI) engine, providing insight into the ion chemistry inside the cylinders during combustion. HCCI engines typically operate at lean equivalence ratios ( ϕ ) at which the ion current becomes increasingly indistinguishable from background noise. This paper investigates the effect of fuel additives on the ion signal at low equivalence ratios, determines side effects of metal acetate addition, and validates numerical model for ionization chemistry. Cesium acetate (CsOAc) and potassium acetate (KOAc) were used as additives to ethanol as the primary fuel. Concentration levels of 100, 200, and 400 mg/L of metal acetate-in-ethanol are investigated at equivalence ratios of 0.08, 0.20, and 0.30. The engine experiments were conducted at a boosted intake pressure of 1.8 bar absolute and compared to naturally aspirated results. Combustion timing was maintained at 2.5° after top-dead-center (ATDC), as defined by the crank angle degree (CAD) where 50% of the cumulative heat release occurs (CA50). CsOAc consistently produced the strongest ion signals at all conditions when compared to KOAc. The ion signal was found to decrease with increased intake pressure; an increase in the additive concentration increased the ion signal for all cases. However, the addition of the metal acetates decreased the gross indicated mean effective pressure (IMEP g ), maximum rate of heat release (ROHR), and peak cylinder pressure. Experimental results were used to validate ion chemistry mechanisms for cesium and potassium using a single-zone numerical engine model.

Petroleum coke (petcoke) is a by-product of heavy petroleum refining, with heating values comparable to that of coal. It is readily available in oil-producing countries such as the United States of America (USA) and the Kingdom of Saudi Arabia (KSA) at minimum costs and can be used as an inexpensive fossil fuel for power generation. Oxy-petcoke combustion is an attractive CO2 capture option as it avoids the use of additional absorption units and chemicals, and results in a CO2 + H2O flue gas stream that is compressed and dehydrated in a CO2 capture and purification unit (CO2CPU). The additional cost of the CO2CPU can be reduced through high pressure combustion. Hence, this paper reports a techno-economic analysis of an oxy-petcoke plant with CO2 capture simulated at pressures between 1 and 15 bars in Aspen PlusTM based on USA and KSA scenarios. Operating at high pressures leads to reduced equipment sizes and numbers of units, specifically compressors in CO2CPU, resulting in increased efficiencies and decreased costs. An optimum pressure of ~10 bars was found to maximize the plant efficiency (~29.7%) and minimize the levelized cost of electricity (LCOE), cost of CO2 avoided and cost of CO2 captured for both the USA and KSA scenarios. The LCOE was found to be moderately sensitive to changes in the capital cost (~0.7% per %) and increases in cost of petcoke (~0.5% per USD/tonne) and insensitive to the costs of labour, utilities and waste treatment.

Carbon capture has been deemed crucial by the Intergovernmental Panel on Climate Change if the world is to achieve the ambitious goals stated in the Paris agreement. A deeper integration of renewable energy sources is also needed if we are to mitigate the large amount of greenhouse gas emitted as a result of increasing world fossil fuel energy consumption. These new power technologies bring an increased need for distributed fast dispatch power and energy storage that counteract their intermittent nature. A novel technological approach to provide fast dispatch emission free power is the use of the Argon Power Cycle, a technology that makes carbon capture an integral part of its functioning principle. The core concept behind this technology is a closed loop internal combustion engine cycle working with a monoatomic gas in concert with a membrane gas separation unit. By replacing the working fluid of internal combustion engines with a synthetic mixture of monoatomic gases and oxygen, the theoretical thermal efficiency can be increased up to 80%, more than 20% over conventional air cycles. Furthermore, the absence of nitrogen in the system prevents formation of nitrogen oxides, eliminating the need for expensive exhaust gas after-treatment and allowing for efficient use of renewable generated hydrogen fuel. In the case of hydrocarbon fuels, the closed loop nature of the cycle affords to boost the pressure and concentration of gases in the exhaust stream at no penalty to the cycle, providing the driving force to cost effective gas membrane separation of carbon dioxide. In this work we investigated the potential benefits of the Argon Power Cycle to improve upon current stationary power generation systems regarding efficiency, air pollutants and greenhouse gas emissions. A cooperative fuel research engine was used to carry out experiments and evaluate engine performance in relation to its air breathing counterpart. A 30% efficiency improvement was achieved and results showed a reduction on engine heat losses and an overall increase on the indicated mean effective pressure, despite the lesser oxygen content present in the working fluid. Greenhouse gas emissions were reduced as expected due to a substantial increase in efficiency and nitric oxides were eliminated as it was expected. Numerical simulation were carried out to predict the performance and energy penalty of a membrane separation unit. Energy penalties as low as 2% were obtained capturing 100% of the carbon dioxide generated.

Autoignition in HCCI engines is known to be controlled by the combustion kinetics of the in- cylinder fuel/air mixture which is highly influenced by the amount of low-temperature and intermediate-temperature heat release (LTHR and ITHR) that occurs. At lower intake pressures (typically 1.8 bar absolute) gasoline behaves as a two-stage heat release fuel. Furthermore, ethanol blending strongly affects heat release characteristics, and this warrants further investigation. This paper experimentally investigates the conditions under which gasoline transitions from a single-stage heat release fuel to a two-stage heat release fuel as intake pressure is increased. Experiments were performed in single-cylinder HCCI engine fueled with two research-grade gasolines, FACE A and FACE C. These gasolines were tested neat, with 10% and 20% (by volume) ethanol addition. In addition, these results were compared to results previously obtained for PRF 85, and new results for PRF 84 with 10% and 20% ethanol addition. Moreover, the engine experiments were supported by rapid compression machine (RCM) ignition delay data for the same fuels. The engine experiments revealed that there were minimal differences between the heat release profiles of the two gasolines, FACE A and FACE C, which was confirmed by the RCM experiments that showed similar ignition delay data for the two FACE fuels and PRF 84. On the other hand, with ethanol addition to these gasolines and PRF 84, the occurrence of LTHR shifted to higher intake pressures compared to ethanol-free cases, precisely from 1.4 bar intake pressure for neat fuel to 2.2 bar with 20% ethanol. Consequently, the intake temperatures required to achieve constant combustion phasing for all mixtures were drastically altered. Simulations using a detailed chemical kinetic model were utilized to understand the effects of ethanol blending on the ignition characteristics of PRF 84. The addition of ethanol was found to act as a radical sink where it inhibits the radical pool formation during the low (

This review work focuses on biofuels with lower viscosity and cetane number and their mode of operation in a diesel engine. Though there were a number of review works describing the production, characterization and utilization of biodiesel, synthesized from vegetable oils, a comprehensive summary on other category of biofuels endowed with lower viscosity and cetane number has not come to light so far. In this backdrop, this review work would bring forth the existence of biofuels having lower viscosity and cetane number, classify them under one category and elucidate their operational feasibility in a diesel engine. Considerably, alcohol based fuels such as methanol, ethanol and butanol, and plant based light biofuels such as eucalyptus oil and pine oil have been chosen and classified as LVLC (less viscous and lower cetane) fuels in the current work. Besides describing the operation feasibility of these fuels, an extensive exploration of their physical, thermal and critical properties as well as their compositional attributes has been made. Despite their distinct properties, these fuels have found use in diesel engine by various strategies and apparently, they could be used in blends with diesel/biodiesel, dual fuel mode and as sole fuel. In this regard, herein, a detailed summary on operation of these fuels in the reported three different modes is clearly explained and their engine characteristics such as performance, combustion and emission are briefed.

An experimental study is presented of unsteady N 2 -in- H 2 jet flames in a co-flow of hot combustion products from lean premixed hydrogen combustion for investigation of the statistical likelihood of autoignition events in the mixing region. The unsteady jet flame is characterized by rapid ignition followed by a gradual blowout of the flame. Audio recordings and Schlieren imaging high speed videos are used in investigating the unsteady flame. The frequency of the blowout re-ignition event is investigated as a function of nitrogen dilution mole fraction ( Y N 2 = 0.180 –0.566), co-flow equivalence ratio ( Φ cf = 0.20 –0.27) and jet velocity ( V jet = 300 –500 m/s). The results from the audio recordings and Schlieren imaging indicate that autoignition dominates the re-ignition. The frequency of ignition increase with increasing nitrogen dilution until a maximum is reached after which it decreases with further nitrogen dilution. For increasing equivalence ratios a higher nitrogen dilution is needed in the jet for the flame to become unsteady. The effect of the nitrogen dilution is explained primarily through a reduction in reaction rates and increased jet momentum. Furthermore, the results suggest that the re-ignition rates are controlled by both chemistry and turbulent mixing. The results from the audio recordings and the Schlieren imaging videos correspond well which validates the use of audio recordings as a diagnostic for studying of unsteady hydrogen jet flames.

Development of SI engines to further increase engine efficiency is strongly affected by the occurrence of engine knock. Engine knock has been widely investigated over the years and the main promoting parameters have been identified as load (temperature and pressure), mixture composition, engine speed, characteristic of the fuel, combustion chamber design, and etc. In this paper a new model for predicting engine knock in 0-D environment is presented. The model is based on the well-known approach of using a Livengood and Wu knock integral. Ignition delay data that are supplied to the knock integral are for specific fuel calculated by detail chemical kinetics and are comprised of low temperature heat release ignition delay and high temperature heat release ignition delay. Next, the cycle to cycle variations of engine and temperature stratification of the end gas have to be taken into account. For temperature stratification a new model is developed which is based on the detail analysis of specific CFD results of several engines at different operating conditions. The validation of the knock prediction model was made by comparisons of the simulation results with the experimental data, for two different fuels (n-heptane and gasoline), showing promising ability of the model to predict the tendency of knocking. The results also showed that the cyclic variability of the knock occurrence and intensity in SI combustion is not only caused by the differences in pressure profile caused by cycle to cycle variations, but also by some other factors.

Measuring the ion current with a sparkplug ion sensor in a homogeneous charge compression ignition (HCCI) engine can be used to investigate the ion chemistry in the cylinders during combustion. HCCI engines are similar to a well-stirred reactor and operate at lean equivalence ratios (ϕ). Under these conditions, the ion current becomes increasingly indistinguishable from background noise. This paper investigates various fuel additive effects on ion signal at low ϕ’s, determines side effects of metal acetate addition, and validates a numerical model. The fuel additives added to ethanol were sodium acetate (NaOAc), potassium acetate (KOAc), and cesium acetate (CsOAc). Concentration levels ranging from 0.5 to 4.9 mmol/L of metal acetate-in-ethanol are investigated over ϕ’s 0.11, 0.22, 0.28, and 0.32. The engine operated under naturally aspirated conditions and maintained a constant timing of 2.5° after top-dead-center (ATDC) at the crank angle degree (CAD) where 50% of the heat release occurs (CA50). CsOAc consistently produced the strongest ion signals, followed by KOAc and NaOAc, which NaOAc had the weakest effect on ion signal. No distinguishable ion signals were measured at ϕ = 0.11, but significant ion signal improvements occurred at ϕ = 0.22 using the fuel additives. However, the addition of the metal acetates decreased heat release rates (HRR) and peak cylinder pressures. Although CsOAc produced the largest signal improvements, it also had the largest decrease in HRR and peak cylinder pressure. Additionally, a single-zone engine model that simulates the chemical kinetics and ion chemistry of KOAc addition is presented and validated with the experimental results.

Ion sensing is a promising approach for cycle resolved combustion phasing in HCCI engines. This paper investigates the fundamental processes affecting the phase difference (Pdelta) between ion current signal phase Ion50 and combustion phase CA50 based on 2 numerical models. One model is used to explore fluid dynamic effects on an HCCI engine. The other model, a 10-zone model, is used to primarily explore the affecting mechanism on Pdelta. Both numerical analysis and experimental results of the ionization process indicate that Pdelta is affected by both flame ionization and fuel heat release process. For fuels with similar octane number (ON), such as gasoline (ON = 97) and ethanol (ON = 107), both the combustion phase CA50 and the ion current signal phase Ion50 retard when the equivalence ratio Φ decreases. However, the CA50 for ethanol fuel retards moderately compared with the gasoline case since the CA50 for ethanol fuel is more sensitive to intake temperature T in rather than Φ . Then larger Pdelta values can be seen in ethanol fueled HCCI engine under lower Φ conditions. For the fuels with different widely octane number, such as gasoline and diesel (ON = 0), their combustion boundary conditions are different in HCCI engines, they produce ions at a different ratio. For diesel fuel, the ion production rate is much lower due to the lower intake temperature and higher compression ratio. Under low Φ conditions, the ion current signal cannot be observed at the beginning of ion concentration increase in diesel fueled HCCI engines, and the Ion50 appears much later compared with the gasoline fueled HCCI engine. As a result, the values of Pdelta increase significantly in the diesel fueled HCCI engine.

This work was sponsored by the Saudi Aramco under the FUELCOM II program and by King Abdullah University of Science and Technology. The computational simulations utilized the clusters at KAUST Supercomputing Laboratory and IT Research Computing.

The effect of the direct injection of hydrogen peroxide into a port-injected methane fueled homogeneous charge compression ignition engine was investigated numerically. The injection of aqueous hydrogen peroxide was implemented as a means of combustion phasing control. A single-cylinder homogeneous charge compression ignition engine (2.43 L Caterpillar) was modeled using the Cantera 2.0 flame code toolkit, the GRI-Mech 3.0 chemical reaction mechanism, and a single-zone slider-crank engine model. Start of injection timing and the amount of injected hydrogen peroxide were manipulated to achieve desired combustion phasing under a wide range of intake temperatures. As the concentration of hydrogen peroxide is increased, the combustion phasing is advanced up to 22° for the conditions investigated in this study. This advancing effect is most pronounced at small concentrations (2O2/kg CH4) and early injection timings (start of injection

This paper describes a numerical study that analyzed the influence of combustion products (CP) concentration on the combustion characteristics (combustion timing and combustion duration) of a biogas fueled homogeneous charge compression ignition (HCCI) engine and the possibility of reducing the high intake temperature requirement necessary for igniting biogas in a HCCI engine by using internal exhaust gas recirculation (EGR) enabled by negative valve overlap (NVO). An engine model created in AVL Boost, and validated against experimental engine data, was used in this study. The results show, somewhat counter-intuitively, that when CP concentrations are increased the required intake temperature for maintaining the same combustion timing must be increased. When greater NVO is used to increase the in-cylinder CP concentration, the in-cylinder temperature does increase, but the chemical dilution influence of CP almost entirely counteracts this thermal effect. Additionally, it has been observed that with larger fractions of CP some instability of combustion in the calculation was obtained which indicates that the increase of internal EGR might produce some combustion instability.

In this article, we present performance results and analysis of a novel rotary lobe expander device. This is part of a larger research effort into the analysis and design of a small-scale solar system that would compete with available distributed technologies for heat and electricity generation. To choose an appropriate working fluid and components for a distributed concentrating solar combined heat and power (DCS-CHP) system, we compared many different working fluids, collectors, and expander choices. Of the expanders analyzed, including piston expanders, radial inflow turbines, Tesla turbines, screw expanders, and scroll expanders, the rotary lobe expander shows the greatest promise in small-scale power applications due to its high efficiency in expanding fluids over large pressure ratios and its low cost to manufacture. This article focuses on testing of a prototype small-scale expander that was chosen because, to date, no suitable commercial product of less than 10 kW has been found for this application. Initial testing was completed with air to get results that should be indicative of future testing with steam. The test system consists of a compressed air expander (a prototype designed by Katrix, Inc. of Australia) connected to an induction motor driven by a variable frequency drive (VFD) that enables expander testing at varying shaft speeds. Results of the expander testing are reported isentropic efficiencies of 22–25%, thermomechanical efficiencies of 80–95%, and pressure ratios of 6–11 at the tested speeds. Despite mixed results from this particular expander, future refinements could lead to a new class of expanders with low cost and high performance for use in solar combined heat and power and waste-heat recovery.

As a result of the energy crisis in recent decades, biofuels have gained importance as an option to diminish the oil dependence of automotive industry. Ethanol is one of these biofuels for which demand around the world has increased in recent years. However, to be used as a fuel, the ethanol must be dehydrated to avoid problems in actual engines, and this step has a high energy cost. To overcome this drawback, some studies have demonstrated the use of wet ethanol in homogeneous charge compression ignition (HCCI) engines. In this work, the production of wet ethanol, using conventional distillation, was studied using rigorous simulation studies and experimental tests in a distillation column. The simulation analysis and experimental validation of the energy requirements to obtain wet ethanol were achieved. The results showed that wet ethanol can be produced by using a distillation column with a small number of stages and low reflux ratios, which results in energy savings. Also, the results indicated that for low purities of the distilled ethanol (wet ethanol), the ratios between the energy required during the distillation process and the energy produced by ethanol during the combustion were low. This result implies that the use of wet ethanol can be considered as realistic option in HCCI engines.

This paper investigates the anti-knock properties of biofuels that can be produced from microorganism metabolic processes. The biofuels are rated using Research Octane Number (RON) and Blending Research Octane Number (BRON), which determine their potential as additives for fuel in spark ignition (SI) engines. Tests were conducted using a single-cylinder Cooperative Fuel Research (CFR) engine and performance of the biofuels was compared to primary reference fuels (PRFs). The investigated fuels include 3-methyl-2-buten-1-ol, 3-methyl-3-buten-1-ol, 2-methylpropan-1-ol (isobutanol), and limonene. Results show that 3-methyl-2-buten-1-ol, 3-methyl-3-buten-1-ol, and 2-methylpropan-1-ol (isobutanol) sufficiently improve the anti-knock properties of gasoline.

The enhancement of laminar flame development using microwave-assisted spark ignition has been investigated for methane–air mixtures at a range of initial pressures and equivalence ratios in a 1.45 l constant volume combustion chamber. Microwave enhancement was evaluated on the basis of several parameters including flame development time (FDT) (time for 0–10% of total net heat release), flame rise time (FRT) (time for 10–90% of total net heat release), total net heat release, flame kernel growth rate, flame kernel size, and ignitability limit extension. Compared to a capacitive discharge spark, microwave-assisted spark ignition extended the lean and rich ignition limits at all pressures investigated (1.08–7.22 bar). The addition of microwaves to a capacitive discharge spark reduced FDT and increased the flame kernel size for all equivalence ratios tested and resulted in increases in the spatial flame speed for sufficiently lean flames. Flame enhancement is believed to be caused by (1) a non-thermal chemical kinetic enhancement from energy deposition to free electrons in the flame front and (2) induced flame wrinkling from excitation of flame (plasma) instability. The enhancement of flame development by microwaves diminishes as the initial pressure of the mixture increases, with negligible flame enhancement observed above 3 bar.

The purpose of this research is to investigate the impact of fuel composition on auto-ignition in homogeneous charge compression ignition (HCCI) engines in order to develop a future metric for predicting fuel performance in future HCCI engine technology. A single-cylinder, variable compression ratio engine operating as an HCCI engine was used to test reference fuels and gasoline blends with octane numbers (ON) ranging from 60 to 88. Correlations between fuel composition, ON, and two existing methods for predicting fuel auto-ignition in HCCI engines (Kalghatgi's octane index and Shibata and Urushihara's HCCI index) are investigated. Results show that octane index and HCCI index poorly predict the impact of fuel composition on auto-ignition for fuels with the same ON. The effect of ethanol in delaying auto-ignition depends on the composition of the original gasoline blend; the same is true for the addition of naphthenes. Low-temperature heat release (LTHR) correlates well with auto-ignition for gasoline fue...

This work was funded by competitive research funding from King Abdullah University of Science and Technology (KAUST) under the Clean Combustion Research Center's Future Fuels program. We also acknowledge funding from KAUST and Saudi Aramco under the FUELCOM program. Finally, we would like to express our gratitude to our Research Technician, Adrian. I. Ichim, for his support in carrying out the engine experiments at KAUST engine lab.

In this research, the flow and ignition properties of vegetable oil (VO) are improved by blending it with diethyl ether (DEE). DEE, synthesized from ethanol, has lower viscosity than diesel and VO. When DEE is blended with VO, the resultant DEEVO mixtures have favorable properties for compression ignition (CI) engine operation. As such, DEEVO20 (20% DEE + 80% VO) and DEEVO40 (40% DEE + 60% VO) were initially considered in the current study. The viscosity of VO is 32.4*10−6 m2/s; the viscosity is reduced with the increase of DEE in VO. In this study, our blends were limited to a maximum of 40% DEE in VO. The viscosity of DEEVO40 is 2.1*10−6 m2/s, which is comparable to that of diesel (2.3*10−6 m2/s). The lower boiling point and flash point of DEE improves the fuel spray and evaporation for DEEVO mixtures. In addition to the improvement in physical properties, the ignition quality of DEEVO mixtures is also improved, as DEE is a high cetane fuel (DCN = 139). The ignition characteristics of DEEVO mixtures were studied in an ignition quality tester (IQT). There is an evident reduction in ignition delay time (IDT) for DEEVO mixtures compared to VO. The IDT of VO (4.5 ms), DEEVO20 (3.2 ms) and DEEVO40 (2.7 ms) was measured in IQT. Accordingly, the derived cetane number (DCN) of DEEVO mixtures increased with the increase in proportion of DEE. The reported mixtures were also tested in a single cylinder CI engine. The start of combustion (SOC) was advanced for DEEVO20 and DEEVO40 compared to diesel, which is attributed to the high DCN of DEEVO mixtures. On the other hand, the peak heat release rate decreased for DEEVO mixtures compared to diesel. Gaseous emissions such as nitrogen oxide (NOX), total hydrocarbon (THC) and smoke were reduced for DEEVO mixtures compared to diesel. The physical and ignition properties of VO are improved by the addition of DEE, and thus, the need for the trans-esterification process is averted. Furthermore, this blending strategy is simpler and enables operation of straight run oils and fats in CI engine, replacing diesel completely.