Homogeneous Charge Research Articles

Discharge dynamics of primary and secondary streamers in a repetitively pulsed surface dielectric barrier discharge

Discharge dynamics of primary and secondary streamers in a repetitively pulsed surface dielectric barrier discharge (SDBD) are investigated based on experimental and numerical simulations. Plasma propagation and coupled energy of the primary streamer are restricted in subsequent pulses, but the deposited energy of the secondary streamer increases. When the pulse repetition frequency reduces, a longer plasma length and higher average velocity of the primary streamer can be observed, but the influences on propagation length and velocity of the secondary streamer are very limited. These phenomena indicate that the residual surface charges left by the previous pulse should have a critical effect on the discharge dynamics of subsequent discharges. In order to have a deeper insight into the influence of residual surface charges in a repetitively pulsed SDBD, a numerical model characterized with a pre-charging of homogeneous charge accumulated on the dielectric surface is built. Pre-charging of positive charges deposited on the dielectric surface can inhibit the electric field of applied voltage, resulting in a decrease in the expansion of the primary streamer and the positive peak of current, which is in qualitative agreement with the experimental measurements. However, there is an opposite evolution rule when the negative charges are deposited on the dielectric surface. Although the electric field strength of the secondary streamer is enhanced for a high pre-charging value, there is no great impact on the negative peak of current during the secondary streamer due to the remaining heavy mass ions.

Influence of cobalt chromium nanoparticles in homogeneous charge compression ignition engine operated with citronella oil

AbstractStringent emission standards and greater fuel economy have forced scientists to develop an advanced combustion technology (homogeneous charge compression ignition; HCCI) useful in internal combustion engines in the future. Citronella biodiesel prepared through transesterification process which is auspicious an energy source for the CI engine. Cobalt chromium nanoparticles were mixed with the biodiesel at 30 ppm with the help of an ultrasonicator. The present experimental investigation was conducted to analyze various performance (brake thermal efficiency (BTE) and brake‐specific fuel consumption (BSFC)), combustion (pressure and heat release rate (HRR)), and emission (unburnt hydrocarbon (UBHC), CO, NOx, and smoke) parameters of the HCCI engine with neat diesel, CBD 5% (citronella biodiesel 5% + 95% diesel), CBD 10% (citronella biodiesel 10% + 90% diesel), CBD 15% (citronella biodiesel 15% + 85% diesel), CBD 20% (citronella biodiesel 20% + 80% diesel), and CBD 15% + C30 (citronella biodiesel 15% + 85% diesel +30 ppm cobalt). To carry out the experiment, a fuel vaporizer was adopted in a 5.2 kW, 1500 rpm, single‐cylinder, four‐stroke, vertical, direct‐injection diesel engine. Nanoparticles were used to improve surface area/volume ratio, heat conduction, and heat transfer rate within the oil layers. The result showed that CBD 15% had given better results than the other citronella biodiesel‐blended fuels. CBD 15% + C30 fuel increased the BTE and HRR by 5.49% and 6.8%, respectively, due to a shorter ignition delay and greater cetane number of the fuel. The percentage of BSFC, UBHC, CO, NOx, and smoke was decreased by 33.33%, 34.32%, 5.1%, and 17.34%, respectively, compared to neat biodiesel in the HCCI engine at 80% load.

An experimental study of performance, combustion and emissions characteristics of an ethanol HCCI engine using water injection

Homogeneous charge compression ignition (HCCI), also known as Controlled Auto-Ignition (CAI), enables combustion with high fuel conversion efficiency and low NOX emissions. It can benefit both spark and compression ignition engines and lessens the demand for expensive exhaust after-treatment systems. However, the HCCI application is restricted due to a limited operating range. Water injection can tackle this problem, which enables higher loads without excessive heat release rates. Although already reported in spark-ignited engines, water injection is still a novelty for HCCI combustion. The water injection strategy is not fully developed for HCCI engines, especially fueled with renewable fuels and using different methods to achieve CAI conditions. Hence, this paper studied the performance, combustion, and emissions characteristics of an ethanol HCCI engine using water injection and total exhaust gas recycling from an adjacent diesel cylinder. HCCI combustion was attained via direct recirculation of exhaust gases from a diesel cylinder, serving as a heat and active radical source for the ethanol charge auto-ignition. Water injection was used for combustion phasing control and load expansion. Detailed combustion and heat release analyses were performed. During the experiments, combustion phasing (CA50) ranged from 2 to 8 crank angle degrees (CAD) ATDC. Water injection reduced the heat release rates and prevented knock, keeping the in-cylinder temperatures below 1850 K. The results indicated that water injection effectively controlled combustion phasing and heat release rate, increasing the maximum operational load threefold. The combustion duration increased with water injection, varying from 6.6 CAD at high loads to 17.0 CAD at low loads. The indicated conversion efficiency was 27% at low loads and achieved the maximum of 39% at 6 bar of indicated mean effective pressure (IMEP). The NOX emissions formed in ethanol HCCI combustion were lower than 0.8 g/kWh.

An Experimental and Modeling Study on the Combustion of Gasoline-Ethanol Surrogates for HCCI Engines

As an effective clean fuel, ethanol has the characteristics of improving antiknock quality and reducing emissions. It is an ideal antiknock additive for Homogeneous Charge Compression Ignition (HCCI) engines. The oxidation of gasoline-ethanol surrogates in HCCI engines is a very complex process which is dominated by the reaction kinetics. This oxidation process directly determines the performance and emissions of HCCI engines. Coupling the computational fluid dynamic (CFD) model with the gasoline-ethanol surrogate mechanism can be used for fuel design, so the construction of a reduced mechanism with high accuracy is necessary. A mechanism (278 species, 1439 reactions) at medium and low temperatures and experiments in a HCCI engine for the oxidation of gasoline-ethanol surrogates were presented in this paper. Directed relation graph with error propagation (DRGEP) method and quasi-steady-state assumption (QSSA) method were used in order to get a reduced model. Then, the kinetics of the vital reactions related to the formation and consumption of H and OH were adjusted. To validate the model, the HCCI experiments for the oxidation of gasoline-ethanol surrogates were conducted under different operating conditions. The verification result indicated that the present model can predict the oxidation process of gasoline-ethanol effectively.

Dynamic measurement with in-cycle process excitation of HCCI combustion: The key to handle complexity of data-driven control?

Homogeneous Charge Compression Ignition (HCCI) is a low temperature combustion technique with a high potential for reducing emissions while simultaneously improving fuel consumption. However, the high sensitivity to changing boundary conditions and low combustion stability at the edges of the operating range has lead to implementation challenges. Additionally, cyclic coupling through internal exhaust gas recirculation causes cyclic variations of the process, resulting in incomplete combustion, or even misfiring. Thus, consecutive cycles must be decoupled to increase the process stability. To achieve an accurate description of the coupling effects on a cycle-to-cycle and an inner-cyclic timescale, a novel measurement methodology is presented to generate data with a high variance. For this purpose, an active process excitation is performed to capture all relevant interactions between operating and feedback variables to enable modeling of the coupling effects on both timescales. To demonstrate the potential of the methodology, the generated data is used to design multiple input, multiple output (MIMO) models for both cyclic and inner-cyclic timescales. Artificial neural networks are then utilized to address the highly nonlinear process by taking advantage of the large amount of training data. Inverse process models are then used to implement a pure cycle-to-cycle and a multiscale MIMO closed-loop controller. Compared to state-of-the-art rule-based control approaches, the process stability and its thermodynamic efficiency are significantly improved. For the multiscale MIMO controller, a reduction of the standard deviation of the indicated mean effective pressure and the combustion phasing of more than 65% is achieved. In particular, the additional inner-cyclic feedback loop achieves a remarkable reduction of the standard deviation of approximately 35% and a 1.2% higher indicated efficiency compared to the cycle-to-cycle MIMO controller. The dynamic measurement with active in-cycle process excitation has proven to be an enabler for data-driven MIMO control of HCCI on multiple timescales.

Effect of Combustion Boundary Conditions and n-Butanol on Surrogate Diesel Fuel HCCI Combustion and Emission Based on Two-Stroke Diesel Engine

The combustion and emission characteristics of surrogate diesel fuel homogeneous charge compression ignition (HCCI) with different combustion boundary conditions and n-butanol (NB) mixing ratios are studied in this work. Engine data of a two-stroke low-speed direct-injection marine diesel engine were selected for the reactor. HCCI combustion was achieved by compressing a completely homogeneous mixture of fuel and air. The results show that NO emissions decrease slightly with the increase of initial boundary pressure at a constant equivalence ratio and initial temperature. In addition, the different initial boundary temperature has little effect on NO emission. The results also indicate that the ignition delay time of the mixed fuel rises with the increase of n-butanol mixing ratio. The emissions and reaction rate of NOx reduce significantly with the increase of n-butanol percentage in surrogate diesel fuel and n-butanol mixing combustion at a constant equivalence ratio and total mole fraction. Meanwhile, CO2 emissions also decrease significantly with the increase of n-butanol mixing ratio.

Multi-scale assessment and multi-objective optimization of a novel solid oxide fuel cell hybrid power system fed by bio-syngas

Nowadays, thermal power generation using fossil fuels is still the main way for electricity supply, resulting in serious environmental pollution and energy consumption. The research on new power generation and alternative energy is urgently needed to conduct. In this paper, a new power supply system combined biomass and fuel cell with waste heat recovery is proposed and analyzed. The system uses agricultural waste as energy source, providing gas fuel for solid oxide fuel cell through the biomass gasification. In addition, the homogeneous charge compression ignition engine can utilize unreacted fuel, and the waste heat energy in flue gas is recovered by the combination of supercritical carbon dioxide cycle and absorption refrigeration cycle. Under selecting working condition, the engine and bottom cycles brings an improvement of 11.10% in thermal efficiency, and the total fuel efficiency can reach 59.35%. Besides, the payback time of this system is nearly 60% shorter than the traditional system, with a minimum of 1.77 years. The whole system realizes the energy cascade utilization, being more efficient and cleaner, and has satisfactory performance.

Homogeneous Charge Transfer Between Reduced Intermediate of Anthraquinones and Dioxygen in Acetonitrile

This work analyzes the electrochemical behavior of anion from anthraquinone,1-amino-4-hidroxy-2-phenoxyanthraquinone, trade name, disperse red 60 (DR60), in the presence of dioxygen and water in acetonitrile solutions. The interaction of the DR60 radical anion with water in the system, verified by digital fitting procedures, affects the first reduction process of DR60. A process of homogeneous charge transfer between the reduced intermediate of the anthraquinone DR60 with dioxygen was identified by cyclic voltammetry and bulk electrolysis. The value of the equilibrium constant of the homogeneous charge transfer was determined (K eq = 2.013)

Optimization of Performance Characteristics of Homogeneous Charge Compression Ignition Engine with Biodiesel using Artificial Neural Network (ANN) and Response Surface Methodology (RSM)

Optimization of Performance Characteristics of Homogeneous Charge Compression Ignition Engine with Biodiesel using Artificial Neural Network (ANN) and Response Surface Methodology (RSM)

Experimental study on controlled hot surface assisted compression ignition (HSACI) in a naturally aspirated single cylinder gas engine

Homogeneous charge compression ignition (HCCI) promises low [Formula: see text] emissions and high efficiency due to fast combustion at low temperatures. However, the control of combustion timing represents a serious challenge due to the lack of dedicated ignition control parameters. This challenge is addressed in this work by means of a hot surface ignition (HSI) system, whose core element consists of a shielded, electrically heated ceramic glow plug. In this approach, termed as hot surface assisted compression ignition (HSACI), a small portion of mixture is thought to ignite in the vicinity of the shielded glow plug and to subsequently propagate to the main combustion chamber in order to initiate bulk-gas auto-ignition. Adjusting the hot surface temperature enables to either advance or retard the onset of combustion and thus, allows to control combustion timing. This paper presents experimental results of initial engine trials, using the HSACI concept in a naturally aspirated single cylinder natural gas engine. Measurements were conducted at a constant engine speed of 1400 l/min and include intake air temperatures in the range of 150–175°C and relative air-fuel ratios ([Formula: see text]) from 2.0 to 2.8. Results show that the HSI system enables combustion under conditions, which do not allow for pure HCCI operation. Moreover, the combustion timing can be actively controlled within certain limits by changing the HSI temperature. Increasing cycle-to-cycle variations limit stable operation at lower temperatures, while a transition to pure HCCI is found at intake temperatures beyond 170°C. The applicable [Formula: see text] range is limited by knocking or uncontrolled combustion toward the rich side and instable operation toward the lean side. Loss analysis points out that wall heat flow and imperfect combustion represent the dominant loss mechanisms. Heat release analysis reveals two pronounced phases, indicating initial flame propagation and subsequent auto-ignition similar to spark assisted compression ignition (SACI).

Research on Homogeneous Charge Compression Ignition Combustion of Intake Port Exhaust Gas Recirculation Based on Cam Drive Hydraulic Variable Valve Actuation Mechanism

The thermal efficiency of an efficient gasoline engine is only about 40% and it will produce a large number of harmful products. Curbing harmful emissions and enhancing thermal efficiency have always been the goals pursued and emission regulations are also being tightened gradually. As one of the main consumers of fossil fuels, automobile engines must further reduce fuel consumption and emissions to comply with the concept of low-carbon development, which will also help them compete with electric vehicles. Homogeneous charge compression ignition (HCCI) combustion combined with variable valve actuation (VVA) technology is one of the important ways to improve engine emissions and economy. HCCI combustion based on VVA can only be realized at small and medium loads. The actual application on the entire vehicle needs to be combined with spark ignition (SI) combustion to achieve full working condition coverage. Therefore, HCCI combustion needs fast valve response characteristics; however, the valve lift and timing of the existing VVA mechanisms are mostly controlled separately, resulting in poor valve response. In order to solve this problem, the cam driven hydraulic variable valve actuation (CDH-VVA) mechanism was designed. The valve lift and timing can be adjusted at the same time and the switching of valve lift and timing can be completed in 1~2 cycles. A set of combustion mode switching data is selected to show the response characteristics of the CDH-VVA mechanism. When switching from spark ignition (SI) to HCCI, it switches to HCCI combustion after only one combustion cycle and it switches to stable HCCI combustion after two combustion cycles, which proves the fast response characteristics of the CDH-VVA mechanism. At the same time, the CDH-VVA mechanism can form the intake port exhaust gas recirculation (EGR), as one type of internal EGR. This paper studies the HCCI combustion characteristics of the CDH-VVA mechanism in order to optimize it in the future and enable it to realize more forms of HCCI combustion. At 1000 rpm, if the maximum lift of the exhaust valve (MLEV) is higher than 5.0 mm or lower than 1.5 mm, HCCI combustion cannot operate stably, the range of excess air coefficient (λ) is largest when the MLEV is 4.5 mm, ranging from 1.0~1.5. Then, as the MLEV decreases, the range of λ becomes smaller. When the MLEV drops to 1.5 mm, the range of λ shortens to 1.0~1.3. The maximum value of the MLEV remains the same at the three engine speeds (1000 rpm, 1200 rpm and 1400 rpm), which is 5.0 mm. The minimum value of the MLEV gradually climbs as the engine speed increase, 1000 rpm: 1.5 mm, 1200 rpm: 2.0 mm, 1400 rpm: 3.0 mm. With the increase of engine speed, the range of indicated mean effective pressure (IMEP) gradually declines, 3.53~6.31 bar (1000 rpm), 4.11~6.75 bar (1200 rpm), 5.02~6.09 bar (1400 rpm), which proves that the HCCI combustion loads of the intake port EGR are high and cannot be extended to low loads. The cyclic variation of HCCI combustion basically climbs with the decrease of the MLEV and slightly jumps with the increase of the engine speed. At 1000 rpm, when the MLEV is 5.0 mm, the cyclic variation range is 0.94%~1.5%. As the MLEV drops to 1.5 mm, the cyclic variation range rises to 3.5%~4.5%. Taking the maximum value of the MLEV as an example, the cyclic variation range of 1000 rpm is 0.94%~1.5%, 1200 rpm becomes 1.5%~2.3% and 1400 rpm rises to 2.0%~2.5%.

Investigations on load range extension of a homogeneous charge compression ignited light-duty diesel engine operated with diisopropyl ether and gasoline blends

A major obstacle for commercial implementation of homogeneous charge compression ignition (HCCI) combustion mode is a narrow operating load range. Several thermal and fuel management strategies have been investigated so far to address the shortcomings of HCCI, among which fuel management strategies are generally more effective. The present study intends to utilize high volatile, optimum reactivity fuel to extend the operating load range of a light-duty diesel engine operated in HCCI mode. Experiments are conducted at the rated engine speed, and varying load conditions. The tested fuels include blends of gasoline and diisopropyl ether and the additive 2-ethyl hexyl nitrate (2-EHN). Diisopropyl ether is a low reactivity, and high volatile renewable fuel that has the potential to replace crude oil derived gasoline. In the fuel blends, the proportion of diisopropyl ether is increased from 10% to 60% by volume with a corresponding decrease in gasoline proportion. The results obtained are compared with diesel HCCI considered as the reference. The engine can operate only up to 38% of rated load (2.02 bar brake mean effective pressure) in diesel HCCI mode, which is increased up to 58% of rated load (3.08 bar brake mean effective pressure) with diisopropyl ether-gasoline-2-EHN fuel blends. An improvement in indicated thermal efficiency is observed upon increasing the diisopropyl ether content in the tested fuel blends. The oxides of nitrogen and smoke emissions are low in HCCI with all the fuel blends, while the unburned hydrocarbon and carbon monoxide emissions increase compared to diesel HCCI. Overall, the present research shows that diisopropyl ether is a potential fuel to achieve desired performance and emission targets in an HCCI engine.

Fabricating of grape seed proanthocyanidins loaded Zein-NaCas composite nanoparticles to exert effective inhibition of Q235 steel corrosion in seawater

Grape Seed Proanthocyanidins (GSP), underutilized by-products, exhibit encouraging biological activities, but their structural instability limits practical applications. A solution to this problem was found here by using GSP-loaded zein– sodium caseinate (NaCas) composite nanoparticles. Core-shell biopolymer nanoparticles were fabricated by antisolvent precipitation method to form NaCas stabilized zein core nanoparticles. The GSP-loaded zein-NaCas composite nanoparticles were self-assembled into spherical nanoparticles with homogeneous distribution (PDI around 0.2) and high negative charge (about –30 mV). FTIR analysis indicated that hydrogen bonding, hydrophobic and electrostatic attractions act as the main energy for the formation of colloidal particles. Stability test showed that the particles have stable corrosion inhibition efficiency for Q235 steel within 15 d in a wide range of ionic strength and pH value, and thus can adapt to the changes of seawater environment. Corrosion results manifested that GSP-loaded zein-NaCas composite nanoparticles display good re-dispensability and controlled release performance, whose inhibitive efficiency for Q235 steel in seawater is obviously higher than that of GSP (200 mg/L, 96.06% versus 71.89%).

Comprehensive analysis of combustion phasing of multi-injection HCCI diesel engine at different speeds and loads

Combustion in homogeneous charge compression ignition engines is normally complicated, so the heat release analysis is very significant as it is beneficial for controlling combustion phasing and developing combustion models.The experimental work was carried out on a turbocharged common rail diesel engine. The engine is a water-cooled, 2.776 L, 4-cylinder, and 4-stroke with a multi-injection fuel system. The Apparent Heat Release Rate is computed from the measured in-cylinder pressure at various speeds and loads. The low- and high-temperature reaction events (start and end) and periods, calculated in-cylinder temperature and cumulative fuel burning rate are evaluated and analyzed in both engine crank-angle and time scales. A new correlation considering the effect of engine speed and load on low- and high-temperature reaction periods is proposed. A very good agreement between correlation-predicted and measured and has been achieved (R2 is greater than 0.95), which could be a useful tool in early design calculation, combustion modeling, and control.

A review of internal combustion engines powered by renewable energy based on ethanol fuel and HCCI technology

<abstract> <p>In general, as compared to conventional combustion engines, the homogeneous charge compression ignition (HCCI) engine offers better fuel efficiency, NOx, and particulate matter emissions. The HCCI engine, on the other hand, is not connected to the spark plugs or the fuel injection system. This implies that the auto-ignition time and following combustion phase of the HCCI engine are not controlled directly. The HCCI engine will be confined to a short working range due to the cold start, high-pressure rate, combustion noise, and even knocking combustion. Biofuel innovation, such as ethanol-powered HCCI engines, has a lot of promise in today's car industry. As a result, efforts must be made to improve the distinctive characteristics of the engine by turning the engine settings to different ethanol mixtures. This study examines the aspects of ethanol-fueled HCCI engines utilizing homogenous charge preparation procedures. In addition, comparing HCCI engines to other advanced combustion engines revealed their increased importance and prospective consequences. Furthermore, the challenges of transitioning from conventional to HCCI engines are examined, along with potential answers for future upgrade approaches and control tactics.</p> </abstract>

A review of internal combustion engines powered by renewable energy based on ethanol fuel and HCCI technology

<abstract> <p>In general, as compared to conventional combustion engines, the homogeneous charge compression ignition (HCCI) engine offers better fuel efficiency, NOx, and particulate matter emissions. The HCCI engine, on the other hand, is not connected to the spark plugs or the fuel injection system. This implies that the auto-ignition time and following combustion phase of the HCCI engine are not controlled directly. The HCCI engine will be confined to a short working range due to the cold start, high-pressure rate, combustion noise, and even knocking combustion. Biofuel innovation, such as ethanol-powered HCCI engines, has a lot of promise in today's car industry. As a result, efforts must be made to improve the distinctive characteristics of the engine by turning the engine settings to different ethanol mixtures. This study examines the aspects of ethanol-fueled HCCI engines utilizing homogenous charge preparation procedures. In addition, comparing HCCI engines to other advanced combustion engines revealed their increased importance and prospective consequences. Furthermore, the challenges of transitioning from conventional to HCCI engines are examined, along with potential answers for future upgrade approaches and control tactics.</p> </abstract>

Design of broadband terahertz vector and vortex beams: I. Review of materials and components

In this paper, we review the existing approaches for vortex and vector beam shaping and generation in the terahertz frequency range. The particular focus of this review is on the possibility of homogeneous topological charge formation in the ultra-wide spectral interval inherent to ultrashort terahertz pulses. We review the available materials and components, analyse proposed and potentially possible solutions for broadband terahertz vortex and vector beam shaping, compare all developed approaches, and put forward a unified concept for constructing passive shapers of such beams from the existing component base.

Experimental Study of Homogeneous Charge Compression Ignition in a Light-Duty Diesel Engine Operated with Commercial Gasoline-Ethanol

Experimental Study of Homogeneous Charge Compression Ignition in a Light-Duty Diesel Engine Operated with Commercial Gasoline-Ethanol

A review on butanol properties, production and its application in internal combustion engines

The automotive vehicle markets are full of the application of internal combustion engines (ICE). Although, there is a very small share of battery operated engines that exist but it is in the developing stage and suffering from some challenges. Most vehicles are either SI engine or CI engine driven vehicles. The conventional fossil fuels petrol and diesel are the lifeline of these engines. The growing demand, increasing prices and harmful effects from the application of these fuels has raised concern over the use of it. Butanol is an alcohol based bio-fuel that presents the potential to overcome the negative aspects of traditional fuels and can serve the purpose of clean, efficient and environmentally friendly renewable alternative fuel. This review article includes the properties of butanol, its superiority over the other alcohol fuels like methanol and ethanol, its production method especially the ABE fermentation process and, its application and implementation in ICE as a neat fuel and as a blend. The neat butanol or its blend with petrol or diesel shows some advantages but to get more benefits from the application of butanol as engine fuel it needs to be used with innovative combustion methods. The low temperature combustion (LTC) and their different forms like homogeneous charge compression ignition (HCCI) and reactivity controlled compression ignition (RCCI) are the advanced combustion techniques in which butanol fueled operation offers more benefits as compared to butanol fueled SI and CI engines. In recent years, the potential of n-butanol (an isomer of butanol) is being investigated extensively in HCCI and RCCI engines as it shows excellent features like a great reduction in NOx and smoke emissions and higher thermal efficiency.

A Technical Review – Performance of Homogeneous Charge Compression Ignition (HCCI) Combustion in Diesel Engine with Alternative Fuel

A Technical Review – Performance of Homogeneous Charge Compression Ignition (HCCI) Combustion in Diesel Engine with Alternative Fuel