High Pressure Rise Rate Research Articles

Effects of buoyancy on the spherical flame and explosion pressure of a CH4 mixture under dilution conditions

To determine the effects of buoyancy on the spherical flame and explosion pressure under dilution conditions, a series of explosion experiments were conducted in a 20-L spherical container. The schlieren technique was used to record CH4 flames to assess the buoyancy effect. The change in the explosion pressure was recorded and correlated with the flame shape to analyze the explosion characteristics. The methane explosion occurred in two stages: initial ignition and flame development. During initial ignition, the addition of CO2 caused the flame buoyancy to increase considerably. Flames with different buoyancies had different shapes, such as spherical, ellipsoidal, and “ω” shapes. The radius of the flame at 12 mm may serve as the threshold for the onset of buoyancy effects; once the radius exceeds this value, the flame could deform due to buoyancy effects. Increasing the added CO2 concentration caused the buoyancy effect to be enhanced and appear at a very low radius of the flame. The combined effects of buoyancy and dilution reduced the flame expansion speed. The difference between the horizontal and upward expansion speeds linearly increased with the CO2 concentration. At a high CO2 concentration, the flame stagnated at speeds below 0.5 m/s. During flame development, CO2 addition made the flame surface smoother. Suppressing the cellular flame structure delayed the maximum explosion pressure rise rate and reduced the pressure peak. A coupled analysis of the flame shape and the maximum explosion pressure rise rate showed a dense cellular structure for a high explosion pressure rise rate and a smooth flame surface for a low maximum explosion pressure rise rate. The size and number of cellular structures for different mixtures were similar at a fixed maximum explosion pressure rise rate.

Investigation of injection parameters coupled with fuel reactivity on combustion and emissions in dual direct-injection GCI engine

Fuel injection parameters and fuel reactivity significantly affect engine performance, combustion, and emissions. The dual direct-injection strategy could compensate for the insufficient heat release rate to improve the gasoline compression ignition (GCI) mode with medium injection pressure for high loads. This research aims to couple injection parameters and fuel reactivity to optimize the combustion, emissions, and engine performance of the dual direct-injection GCI mode at high loads. The effect of research octane number (RON) of gasoline, injection timing, and injection pressure of dual injection system on combustion and emissions was investigated. Results show that the optimized dual direct-injection GCI mode can simultaneously achieve high thermal efficiency, low emissions, and low maximum pressure rise rate (MPRR) at high loads with the maximum indicated mean effective pressure (IMEP) of about 16 bar with indicated thermal efficiency (ITE) of 48.5%. Delaying the injection timing of injector-1 reduced the peak pressure (Ppeak), MPRR, and NOx emissions. Ppeak, CO, NOx, and indicated specific fuel consumption (ISFC) decreased compared to the dual-injector simultaneous injection case when the injection timing of injector-2 was retarded to between 5 and 10°CA ATDC. Increasing the injection pressure of injector-2 reduced CO, THC, ISFC, and particulate emissions. Lower RON gasoline obtains higher ITE while higher RON gasoline obtains lower particulate emissions.

Machine learning approaches for identification of heat release shapes in a low temperature combustion engine for control applications

This paper presents the application of machine learning classification algorithms to identify and classify different heat release rate (HRR) shapes to control the combustion for an optimal multi-mode low-temperature combustion (LTC) engine operation. Low-temperature combustion engine produces low nitrogen oxides (NOx) and soot emissions and offers high thermal efficiency. But high in-cylinder pressure rise rates limit the operating range of the LTC engine. Therefore, it is imperative to control combustion in the LTC engine for safe operation. To this end, the HRR traces for over six hundred engine operating conditions are classified using supervised (i.e., Decision Tree, K-Nearest Neighbors (KNN), and Support Vector Machines (SVM)) and unsupervised (i.e., Kmeans clustering) machine learning approaches to segregate different combustion regimes based on HRR shape. Kmeans clustering was not successful in classifying the HRR shapes. Among different supervised machine learning techniques, SVM has proved to be the best method, having an overall classifier prediction accuracy of 92.4% for identifying the distinct shapes using normalized HRR data. In addition, three classifiers have been trained based on the combustion parameters and control inputs. These classifiers are then used as scheduling variables to develop predictive models. A model predictive control (MPC) framework is developed to control multi-mode LTC engine on cycle-to-cycle basis. The MPC framework achieved the simultaneous reference tracking of combustion phasing (CA50) and indicated mean effective pressure (IMEP) while constraining maximum pressure rise rate (MPRR) below 8 bar/CAD.

Study on the Effect of Coupled Internal and External EGR on Homogeneous Charge Compression Ignition under High Pressure Rise Rate

This paper investigated the effects of exhaust gas recirculation (EGR) on homogeneous charge compression ignition (HCCI) combustion in internal combustion engines. The exhaust valve closing (EVC) timings were scanned to obtain a set of baseline operating points for HCCI, and the coupling control of the internal and external EGR was explored. The results indicate that external EGR delays HCCI ignition timing and slows down the combustion speed. As the internal EGR rate increases, the maximum external EGR ratio that can be tolerated decreases. For HCCI detonation operating points with low internal EGR rates, the addition of up to 10% of external EGR can control the pressure rise rate peak to less than 10 bar/°CA, resulting in reduced fuel consumption and increased indicated mean effective pressure (IMEP). However, for HCCI operating points with high internal EGR rates, the effect of external EGR is mainly observed in the control of the pressure rise rate, with limited increase in IMEP. Additionally, an increasing external EGR rate leads to a significant decrease in nitrogen oxide (NOx) emissions, while carbon monoxide (CO) and hydrocarbon (HC) emissions slightly increase before engine misfire occurs. These findings suggest that the coupling control of internal and external EGR should be explored further, particularly in relation to reducing the negative valve overlap (NVO) angle and improving combustion efficiency.

Research and Development of Hydrogen-Fueled Internal Combustion Engines in China.

Energy shortages and environmental problems have brought many challenges to China's development. In the field of transport, hydrogen energy has become a new type of energy that people pay attention to due to its easy production and nonpolluting generation. The use of hydrogen as a fuel in internal combustion engines can be a good way to make a low-cost and clean conversion of the current internal combustion engine, thus realizing the application of hydrogen energy in vehicles. In this study, hydrogen-fueled internal combustion engines (HICEs) are the focus. A review and analysis of the topical issues encountered in the developmental research of HICE is presented, such as the optimization control method of the combustion process, mechanism and suppression method of abnormal combustion (preignition, backfire, knock, and high pressure rise rate in early stages of combustion), influence regularity of hydrogen injection parameters and hydrogen injection modes on the formation and combustion performance of H2-air mixture, emissions and control of NOx, formation of H2-air mixture, and combustion cycle variation, among others. Multiyear studies in the hydrogen-fueled engines clearly show that abnormal combustion, as preignition, backfire, and the blockage of intake pipe, is likely to occur at high load, and the H2 injection parameters and the injection modes possess a prominent effect on the engine's performance and the blockage of the intake pipe, which has an important impact on the preignition and backfire, and the optimal control of the combustion process is a valuable method for resolving the contradictions among inhibiting abnormal combustion, the blockage of the intake pipe, and enhancing hydrogen-fueled engine power.

In-cylinder thermochemical fuel reforming for high efficiency in ammonia spark-ignited engines through hydrogen generation from fuel-rich operations

The increasing trend towards global carbon neutrality is driving interest in ammonia fuel as a potential zero-carbon solution for transportation. However, due to the non-ideal combustion characteristics of ammonia, it is necessary to mix it with hydrogen to achieve better engine performance. While generating hydrogen from ammonia on-board is a key technology, there has been limited research in this area, which is hindering the introduction of ammonia engines to the market. This paper proposes an initial study on the feasibility of thermochemical fuel reforming (TFR) technology for generating hydrogen from ammonia fuel-rich operations. A zero-dimensional engine model, validated against experimental results, is used to assess the potential of the TFR approach and identify any barriers to implementation. The results indicate that the optimum air-fuel ratio for hydrogen generation is an equivalence ratio of two, as it maximizes hydrogen production rates while minimizing operational complexities. Moreover, increasing intake temperature, pressure, and compression ratio enhances hydrogen generation from the ammonia-rich mixture. However, owing to the limited reactivity of the ammonia fuel, the rate of hydrogen production remains relatively small (less than 1%/cycle), significantly falling short of the demand. Additionally, the combustion of the fuel-rich mixture in the TFR cylinder results in approximately 20%/cycle of hydrogen in the emitted gases, potentially enhancing the efficiency of working cylinders, but it also poses the risk of engine component failures due to the high pressure rise rate. In conclusion, the use of solely ammonia to produce hydrogen in the TFR cylinder proves to be inefficient, warranting further investigations into the potential benefits of incorporating additives to promote hydrogen production. Alternatively, if a catalyst is utilized to promote hydrogen production from ammonia, a separate electrically heated hydrogen generation system independently of the engine system proves to be more effective, allowing continuous hydrogen production, unlike the intermittent high-temperature environment provided by TFR technology.

Model predictive control of mixing controlled compression ignition operation for low reactivity fuels

Using gasoline or other low reactivity fuels with a pilot injection or port fuel injection in a compression ignition engine has shown great potential in reducing NOx emissions while keeping high thermal efficiency compared to diesel. However, excessive combustion noise is caused by a high maximum pressure rise rate in the cylinder due to the higher fractions of premixed charge of the low-reactivity fuel. This noise can result in structural damage to engine components and as such, combustion noise limits the range of the operating parameters and makes the control of such engines challenging. In this study, a simulation environment was built up in MATLAB/Simulink leveraging a physics-based zero-dimension combustion model to capture the in-cylinder pressure time traces as well as metrics relevant to thermal efficiency and combustion noise. In order to also facilitate the control of emissions, machine learning models were investigated to capture NOx emissions. A kernel-based extreme learning machine (K-ELM) performed best and had a coefficient of correlation (R-squared) of 0.998. The combustion and NOx emission models are valid for not only conventional gasoline fuel but also oxygenated alternative fuel blends at three different pilot injection strategies. In order to track key combustion metrics while keeping noise and emissions within constraints, a model predictive control (MPC) was applied for a compression ignition engine operating with a range of potential fuels and fuel injection strategies. The MPC is validated under different scenarios, including a load step change, fuel type change, and injection strategy change, with proportional–integral (PI) control as the baseline. The simulation results show that MPC reduces about 26% of ringing intensity in the transient process and 17% at the steady state for E30. Generally, MPC can optimize the overall performance through modifying the main injection timing, pilot fuel mass, and exhaust gas recirculation (EGR) fraction.

Experimental Characterization of Hydrocarbons and Nitrogen Oxides Production in a Heavy-Duty Diesel–Natural Gas Reactivity-Controlled Compression Ignition Engine

Reactivity-Controlled Compression Ignition (RCCI) combustion is considered one of the most promising Low-Temperature Combustion (LTC) concepts aimed at reducing greenhouse gases for the transportation and power generation sectors. Due to the spontaneous combustion of a lean, nearly homogeneous mixture of air and low-reactivity fuel (LRF), ignited through the direct injection of a small quantity of high-reactivity fuel (HRF), RCCI (dual-fuel) shows higher efficiency and lower pollutants compared to conventional diesel combustion (CDC) if run at very advanced injection timing. Even though a HRF is used, the use of advanced injection timing leads to high ignition delays, compared to CDC, and generates high cycle-to-cycle variability, limited operating range, and high pressure rise rates at high loads. This work presents an experimental analysis performed on a heavy-duty single-cylinder compression ignited engine in dual-fuel diesel–natural gas mode. The objective of the present work is to investigate and highlight the correlations between combustion behavior and pollutant emissions, especially unburned hydrocarbons (HC) and oxides of nitrogen (NOx). Based on the analysis of crank-resolved pollutants measurements performed through fast FID and fast NOx systems under different engine operating conditions, two correlations were found demonstrating a good accordance between pollutant production and combustion behavior: Net Cyclic Hydrocarbon emission—cyclic IMEP variations (R2 = 0.86), and Cyclic NOx—maximum value of the Rate of Heat Released (R2 = 0.82).

Impact of Ignition Assistant on Combustion of Cetane 30 and 35 Jet-Fuel Blends in a Compression-Ignition Engine at Moderate Load and Speed

Abstract This study investigates the use of a commercial-off-the-shelf (COTS) ceramic glow-plug to assist ignition of jet fuel blends with cetane numbers of 30 and 35, below the minimum cetane number of 40 for #2 diesel. Experiments were carried out on a single-cylinder compression-ignition engine operating at 1200 RPM for single and dual-injection (pilot + main) timing sweeps. The COTS glow-plug, termed the ignition assistant, was operated at varying input power levels between 0 and 70 W (stock maximum power input is 30 W) at each SOI. Results demonstrate that the use of an ignition assistant at the higher input powers (50 and 70 W) enables operation over a wider range of SOI timings where more advanced times are limited by high pressure-rise rates and more retarded times are limited by rapidly increasing coefficient of variation of gross indicated mean effective pressure. Use of the ignition assistant enables stable combustion at later injection timings increasing the operable range of SOI timings. For the CN 30 fuel, at earlier injection timings, pressure traces, and heat release analysis demonstrated the advancement of start of combustion and combustion phasing with the ignition assistant on. At retarded injection timings where combustion would not otherwise occur completely for the CN 30 fuel, operating the ignition assistant at the higher powers enabled combustion phasing to be advanced and combustion to be stabilized at conditions where, with the ignition assistant off, misfire (flameout) would occur. Furthermore, the ignition assistant enabled combustion phasing to follow an approximately linear response with respect to SOI timing over a wider range of SOI times.

Research on Temperature Rise of Type IV Composite Hydrogen Storage Cylinders in Hydrogen Fast-Filling Process

The internal pressure and temperature of type IV on-board hydrogen storage cylinders constantly change during the hydrogen fast-filling process. In this work, a 2D axisymmetric computational fluid dynamics (CFD) model is established to study the temperature rise of hydrogen storage cylinders during the fast-filling process. The hydrogen filling rate, ambient temperature, volume, and hydrogen inlet temperature were investigated to evaluate their effects on temperature rise inside the cylinders. The effects of the inlet pressure rise and pre-cooling patterns on the temperature rise of large-volume type IV hydrogen storage cylinders are analyzed, and the optimal filling strategy is determined. The research results show that a greater filling rate causes a higher hydrogen temperature rise at the end. The ambient temperature increases linearly with the maximum hydrogen temperature and decreases linearly with the state of charge (SOC). As the volume increases, the temperature rise of the cylinder increases. Reducing the inlet hydrogen temperature helps control the temperature rise, and the hydrogen inlet pre-cooling temperature required for large-volume cylinders is lower. If the filling time remains unchanged, a high pressure rise rate should be avoided, and a linear pressure rise pattern is optimal. Reducing the initial cooling energy is key to optimizing the filling strategy.

Risk Assessment of Annular Pressure Caused by Tubing Leakage in Offshore Gas Wells with High CO2

CO2 sequestration is a kind of technology that can effectively mitigate the greenhouse effect, and the wellbore integrity of the storage system is the key issue to ensure successful CCUS. Failure to timely diagnose tubing leakage in offshore gas wells with high CO2 will lead to annular pressure risk and wellbore corrosion problems. The annular pressure caused by tubing leakage is characterized by high pressure and rapid rise rate, resulting in wellhead jacking, gas leakage, and wellbore structure corrosion, which has become the main cause of wellbore integrity failure in offshore gas wells. Therefore, a model of heat and mass transfer and distribution in offshore gas wells was established firstly, and the physical process of gas leakage and accumulation was described based on the pinhole model and the principle of gas PVT characteristics and volume compatibility. The results show that the depth and equivalent size of the leakage point are two important factors affecting the pressure rise process and leakage rate. Taking case well parameters as an example, after inversion calculation, the annulus pressure in case well was 23.0 MPa, the leakage point equivalent diameter was 2.3 mm, the maximum leakage rate was 0.30 m3/min, and the wellbore safety risk is relatively high. Mechanical repair and chemical plugging agent are recommended to seal the tubing leakage. These risk assessment technologies provide reference for wellbore integrity design and management to reduce CO2 leakage risk caused by wellbore integrity failure.

Hydrogen pre-chamber combustion at lean-burn conditions on a heavy-duty diesel engine: A computational study

The combustion of hydrogen generates almost no harmful emissions except for nitric oxides (NOx), which could be effectively eliminated under lean-burn conditions. In particular, the pre-chamber combustion concept has the potential to further extend the lean-burn limit. To pursue a sustainable mode of the powertrain in future transportation, this work intended to investigate the hydrogen pre-chamber combustion concept on a heavy-duty diesel metal engine under lean-burn conditions. By using the CFD modeling method, the pathway to achieving higher engine efficiency along with lower NOx emissions were explored. The results demonstrated that the lean-burn passive pre-chamber combustion effectively restrained the heat release process within the pre-chamber and yielded negligible NOx emissions while degrading complete combustion and combustion stability as a trade-off. To extend the engine operating range, an adequate amount of fuel was introduced into the pre-chamber. Compared to methane, the active pre-chamber combustion of hydrogen exhibited a significantly higher tendency to induce end-gas autoignition owing to its faster heat release within the pre-chamber. The pressure rise rate within the pre-chamber was successfully controlled by adjusting the pre-chamber throat diameter. Higher thermal efficiency was achieved with an increased compression ratio at the same spark ignition timing because of the advanced combustion phasing. However, the operating range was narrowed for the limit of end-gas autoignition and high pressure rise rate.

The effect of one-sided confinement on nappe oscillations in free falling liquid sheet

A thin liquid sheet flowing under the effect of gravity, subjected to one-sided confinement, generates considerable oscillations. These oscillations (called nappe oscillations) are incidental to the interaction of the liquid sheet with the air enclosure present within the confinement. In this regard, a numerical study is presented here involving parametric investigations to establish the effect of the proximity of the liquid sheet to the wall and surface tension on the instability of the liquid sheet. The present study demonstrates that the confinement is responsible for the perturbations near the inlet of the sheet, which then propagates the sheet into the non-linear regime. Moreover, the study on the effect of the proximity of the wall to the liquid sheet depicts that the wall and liquid sheet interact with each other with pressure in the air cushion acting as a liaison between the two. The sheet closer to the wall evolves into the non-linear regime at a preceding time instant due to the higher rate of pressure rise in the air cushion. The liquid sheet oscillations are stabilized for higher values of the surface tension coefficient. The visualization of vortical structures reveals that the vortices are clustered in the confined space, ascending toward the inlet due to higher values of baroclinicity as the sheet gets closer to the wall. On the other hand, the vortices are sparsely distributed in the domain for higher values of the surface tension coefficient.

Comparative Study of Spark-Ignited and Pre-Chamber Hydrogen-Fueled Engine: A Computational Approach

Hydrogen is a promising future fuel to enable the transition of transportation sector toward carbon neutrality. The direct utilization of H2 in internal combustion engines (ICEs) faces three major challenges: high NOx emissions, severe pressure rise rates, and pre-ignition at mid to high loads. In this study, the potential of H2 combustion in a truck-size engine operated in spark ignition (SI) and pre-chamber (PC) mode was investigated. To mitigate the high pressure rise rate with the SI configuration, the effects of three primary parameters on the engine combustion performance and NOx emissions were evaluated, including the compression ratio (CR), the air–fuel ratio, and the spark timing. In the simulations, the severity of the pressure rise was evaluated based on the maximum pressure rise rate (MPRR). Lower compression ratios were assessed as a means to mitigate the auto-ignition while enabling a wider range of engine operation. The study showed that by lowering CR from 16.5:1 to 12.5:1, an indicated thermal efficiency of 47.5% can be achieved at 9.4 bar indicated mean effective pressure (IMEP) conditions. Aiming to restrain the auto-ignition while maintaining good efficiency, growth in λ was examined under different CRs. The simulated data suggested that higher CRs require a higher λ, and due to practical limitations of the boosting system, λ at 4.0 was set as the limit. At a fixed spark timing, using a CR of 13.5 combined with λ at 3.33 resulted in an indicated thermal efficiency of 48.6%. It was found that under such lean conditions, the exhaust losses were high. Thus, advancing the spark time was assessed as a possible solution. The results demonstrated the advantages of advancing the spark time where an indicated thermal efficiency exceeding 50% was achieved while maintaining a very low NOx level. Finally, the optimized case in the SI mode was used to investigate the effect of using the PC. For the current design of the PC, the results indicated that even though the mixture is lean, the flame speed of H2 is sufficiently high to burn the lean charge without using a PC. In addition, the PC design used in the current work induced a high MPRR inside the PC and MC, leading to an increased tendency to engine knock. The operation with PC also increased the heat transfer losses in the MC, leading to lower thermal efficiency compared to the SI mode. Consequently, the PC combustion mode needs further optimizations to be employed in hydrogen engine applications.

Finding a way through the “misty” evaluation of the flammability and explosivity of kerosene aerosols

• JetA1 mist flammability and explosivity are assessed in a confined explosion vessel. • Influence of initial conditions on explosion sensitivity and severity is studied. • JetA1 mists with a small droplet size have a higher rate of pressure rise. • The MIE of JetA1 mist may be lower than that of vapors at low temperatures. • The vapor/liquid ratio of a mist is a key parameter of its explosion severity. In the context of assessing hydrocarbon mist ignition sensitivity and explosion severity, an original test method is proposed, focusing on kerosene JetA1 mists but is applicable to other hydrocarbons. Experiments were carried out in a modified apparatus based on the 20L explosion sphere. Fine control of the gas/liquid ratio and flow rates, the mist concentration, and the ignition energy and duration, was ensured by a specifically customized control system guaranteeing the flexibility and compliance of the test apparatus. The droplet size distribution (DSD) and the level of turbulence of the JetA1 mist cloud were first determined by an in-situ laser diffraction sensor and by Particle Image Velocimetry, respectively. The lower explosive limit (LEL), the minimum ignition energy (MIE), the limiting oxygen concentration (LOC), the maximum explosion overpressure (P max ), and the maximum rate of pressure rise (dP/dt max ) were then determined for different mist concentrations, ambient temperatures, initial turbulence levels, energies, and DSD. Tests showed that the LEL mist of JetA1 mists of an average diameter of 8 µm is around 94 g/m 3 , a value which increases to 220 g/m 3 with increasing DSD. This value also tends to decrease considerably with increasing temperatures. Moreover, at a JetA1 concentration of 125 g/m 3 , P max and dP/dt max as high as 6 bar and 192 bar/s respectively were reached, the latter increasing to about 480 bar/s at T = 60 °C. These mists were shown to be ignitable using energies as low as 200 mJ, which is lower than that of vapors at low temperatures, and a limiting concentration of oxygen of 15.8 % v/v . The potential presence of hydrocarbon mist should therefore be an element that requires reconsidering the classification of hazardous areas. Finally, to stress the influence of the vapor-liquid ratio present in the cloud before ignition on the combustion kinetics, an evaporation model based on the d 2 -law was developed estimating the evaporation time and the vapor quantity at different initial temperatures or droplet diameters. Findings were shown to be well coherent allowing the proposition of a new technique for determining hydrocarbon mist safety criteria. Finally, results have shown that JetA1 mists can ignite at temperatures below the liquid’s flashpoint under varying turbulence levels and droplet size distributions.

Autoignition, knock, detonation and the octane rating of hydrogen

This paper presents an experimental and numerical study of hydrogen’s combustion, autoignition and octane rating. The experiments are conducted in a standard engine that is compliant for rating liquid fuels to the ASTM’s Research Octane Number (RON) method, with minor modifications to enable hydrogen fueling. The numerical analysis is undertaken using a combination of calibrated, two-zone combustion and kinetic modeling of the end-gas. Application of the standard RON method first shows that hydrogen has a RON of 62–64, which is significantly lower than that of standard gasolines. However, this standard RON method requires conditions that are not relevant to practical, hydrogen-fueled engines and, indeed, do not appear to feature autoignition and knock. A set of modified RON tests are therefore undertaken at more practical conditions. These indicate that hydrogen at standard knock intensity and λ=1,1.5 and 2 has a modified RON of 93.7,117 and greater than 120 respectively, spanning the range of λ that match the energy delivered by common SI engine fuels.Together, these results show that hydrogen is significantly more knock-resistant than standard gasolines when providing similar energy to the premixture. Indeed, it should have comparable knock resistance to some high-octane fuels. However, care must be taken when examining hydrogen autoignition, knock and abnormal combustion more generally. Hydrogen’s high flame speeds near stoichiometric conditions can produce high rates of pressure rise at lower compression ratios that can be mistakenly identified as autoignition, even with contemporary in-cylinder pressure measurement, while higher compression ratios near stoichiometric conditions can cause detonation. The identification and avoidance of conventional knock and other forms of abnormal combustion is therefore particularly important for hydrogen fueled engines. This also has significant implications for the development of standard test methods for determining the octane and methane numbers of hydrogen-rich fuel blends.

Experimental Combustion Analysis of a Small Size Diesel Engine Fueled With Tire Derived Fuel/Diesel Fuel Blends

This study aims to analyse the detailed combustion characteristics of tire derived fuel blends (TDF) in small-size DI diesel engines. From this point of view, the refined TDF and reference diesel fuel (No.2 Diesel) were blended in various percentages and tested in a single cylinder naturally aspirated DI diesel engine to clarify its detailed combustion characteristics. The experimental test results point out that ignition delay period is ob-served to be 4.32 CAD (No.2 Diesel fuel), 5.57 CAD (TDF20), 6.56 CAD (TDF40), 8.48 CAD (TDF60), 11.09 CAD (TDF80), and 14.26 CAD (TDF100) for the low engine speeds (1400 rpm). With the increasing TDF in fuel blends and engine speed, the ignition delay period prolongs more, and the total combustion duration shortens. However, due to the excessively long ignition delay period of TDF100, it is not possible to run the test engine at more than 3000 rpm. TDF blends usually demonstrate a longer premixed combustion period than that of No.2 Diesel, while it exhibits a shorter diffusive combustion period. TDF blends also display a higher maximum value of heat release rate (HRRmax), a higher peak value of in-cylinder pressure (Pmax) and a higher rate of pressure rise (dP/dCAD). In addition, combustion events occur late, and the center of combustion moves away from the top dead center into expansion stroke in the case of TDF blends.

Effect of aluminum foam on pressure oscillation of premixed methane-air deflagrations

The effect of aluminum foam on the pressure oscillation of premixed methane-air deflagrations was investigated using experiments performed in an empty duct and a duct with aluminum foam attached to the upper and lower walls. For a fair comparison, the passage areas of the two ducts are identical when considering a 10 mm thickness of the porous medium. The flame propagation, pressure oscillation, and interaction mechanism between the acoustic wave and flame front are discussed by comparing the flame structure and pressure waveform during premixed methane-air mixture deflagration. The results demonstrate that for the empty duct configuration, the flame propagates as a cellular structure and then evolves into an oscillating flame when approaching the closed end of the duct. The coupling effect of the flame and acoustic waves induces the flame to oscillate violently as the distance from the ignition source to the closed end of the duct (i.e., the ignition position) increases to a threshold value. The magnitude of pressure oscillation increases as the distance between the ignition source and the closed end of the duct increases and reaches a maximum when the ignition position is 700 mm from the closed end. Additionally, the pressure oscillation is consistent with the flame oscillation. This oscillation results in a large deflagration pressure and a high rate of pressure rise. By contrast, the aluminum foam-laden duct completely suppresses the oscillation of the premixed methane-air deflagrations for all ignition positions. The aluminum foam inhibits the coupling effect and consequently restrains the prominent deformation and oscillation of the flame front. Flame oscillation vanishes as the acoustic damping coefficient increases. In this case, there is no oscillation and the leading position of the left flame exhibits a linear relationship with time. Whether the foam material has an inhibitive effect on the deflagration pressure depends on the ignition position. The aluminum foam enhances the deflagration pressure when the ignition position is 100 mm from the closed end, with a 29% increase in the maximum overpressure. By contrast, the aluminum foam attenuates the deflagration pressure for other ignition positions, with a maximum drop ratio of 61.7% at the ignition position being 700 mm from the closed end.

Investigation of the chemical effect of pilot injection on main combustion in a gasoline controlled auto-ignition engine by in-cylinder measurements and numerical simulation of H2O2, HO2, and OH radicals

Compared to conventional combustion in gasoline engines, Gasoline Controlled Auto-Ignition (GCAI) has the potential to significantly reduce both fuel consumption and nitrogen oxides (NOX) raw emissions. However, GCAI combustion still has a limited operating range due to limitations in combustion stability at low loads and high rates of cylinder pressure rise at high engine loads. Previous research identified hydrogen peroxide (H2O2) decomposition as an effective means to control GCAI, which is formed among other species with pilot fuel injection during the negative valve overlap (NVO) phase. Since the chemical effect of H2O2 on the main combustion has not been experimentally confirmed so far, the aim of the experimental study described in this paper is to detect H2O2 during early compression using optical methods. This is approached by conducting Photofragmentation Laser-Induced Fluorescence (PFLIF) of H2O2 by a pump laser and simultaneous hydroxyl radical Laser-Induced Fluorescence (OH-LIF) detection in the combustion chamber of a dedicated GCAI single-cylinder research engine at low loads after NVO with pilot injection (PI). Thereto, the pilot injection strategy as well as the global air/fuel ratio (AFR) are varied. Interestingly, no H2O2, hydroxyl (OH) or hydroperoxyl (HO2) constituents were detected under the operating conditions studied, despite relatively high pilot injection fuel masses and a highly accurate H2O2 detection limit of about 1 ppm. Numerical three-dimensional computational fluid dynamics (3D-CFD) combustion simulations using a semi-detailed reaction kinetic mechanism predicted 5–8 times higher H2O2 concentrations than the detection limit, yielding an uncertainty estimate of the numerical methods. Furthermore, the 3D-CFD simulations showed a significant mixture stratification which is a possible reason for the lack of H2O2 detection under these operating conditions.

Comparison of ethanol/diesel fuel dual direct injection (DI2) strategy with reactivity controlled compression ignition (RCCI) in a diesel research engine

The dual direct injection (DI2) strategy is expected to cover the advantages of conventional diesel (CDI) mode while avoiding deficiencies of reactivity controlled compression ignition (RCCI) strategy such as high amount of incomplete combustion emissions and extremely high rate of pressure rise. Therefore, the present study focused on the comparison of combustion characteristics of these combustion modes in a diesel research engine, which was firstly operated under CDI mode at varying loadings and a constant speed of 2400 rpm to establish the reference data. Then, a low pressure port fuel injection (PFI) and high pressure gasoline direct injection (GDI) systems were activated to run on RCCI and DI2 modes, respectively, whereas test engine was already equipped with a common-rail direct injection (CRDI) system for conventional diesel fuel injection. Results showed that both direct and port injection methods increased the in-cylinder pressure (up to 9%) compared to conventional mode. In RCCI combustion, the rate of pressure rise increased more than direct injection and conventional mode. CDI exhibited higher thermal efficiency than RCCI and DI2 modes while both advanced modes were successful in reducing NOx and Smoke Opacity. However, significantly higher CO and unburned HC emissions were observed with both advanced modes in comparison to conventional one. Both CO and unburned HC emissions were reduced by direct injection of ethanol (DI2 strategy) at the rates of 16% and 35% compared with port injection method of RCCI strategy. This is an important finding of this study, which shows that the DI2 strategy has a potential to address a deficiency of RCCI and will bring it closer to its application to practical engines.