Maximum Rate Of Pressure Rise Research Articles

Recent Studies on Alternative Fuel of Dimethyl Ether

With the development of industrialization, a large number of non-renewable fuels (such as coal and crude oil) are consumed, and the harmful substances produced in the combustion process of a large number of fossil fuels have caused serious pollution to the atmosphere, and the harmful gases produced by combustion have caused disastrous damage to the ecological balance. Therefore, finding clean energy and exploring alternative fuels are very important in today's society. This paper mainly reviews the studies on the alternative fuels of dimethyl ether (DME). Firstly, the types of alternative fuels currently researched by society and their respective advantages and disadvantages are analyzed, and the preparation of dimethyl ether and its advantages and disadvantages are analyzed in detail. In addition, the physicochemical properties, combustion and emission characteristics of dimethyl ether and diesel are compared and analyzed. The conclusion is that the injection delay angle of dimethyl ether is larger than that of diesel, the ignition delay period is shorter than that of diesel, and the maximum explosion pressure, maximum pressure rise rate and combustion noise of dimethyl ether are lower than that of diesel. The diffusion combustion speed of DME is faster than that of diesel, and the combustion duration is shorter than that of diesel. At the same time, as an alternative energy, dimethyl ether engine has a significant reduction in NOx emission, a very low level of HC and CO emission, and zero soot emission. In conclusion, the DME engine has good performance and emission characteristics.

Closed-loop Control of SI←→RCCI Mode Transitions in a Multi-Mode Combustion Engine

The primary barrier to implementing the RCCI mode in on-road vehicles is its limited operating range due to excessive pressure rise rates and complexity of combustion control during mode switching. The feasible operating range of the RCCI mode is only a subset of the speed-load range of conventional spark ignition (SI) engines. Therefore, a multi-mode engine concept operating in RCCI and SI modes can cover required engine operating range and can improve engine performance in terms of thermal efficiency and emissions. The goal of this study is to develop a model-based closed loop control of an SI-RCCI multi-mode engine. To this end, a gain scheduled model predictive controller (MPC) is developed for SI-RCCI-SI mode switching. A Kalman filter is designed for state estimations. The control architecture includes; a supervisory controller that determines the optimal operating mode based on the requested engine load and speed, and gain scheduled MPC and a Kalman filter. The controller performance is validated on a 2-liter multi-mode engine for SI-RCCI-SI mode switching at different engine loads (NMEP) and combustion phasings (CA50). The controller is capable of tracking NMEP and CA50 in both modes and during mode transitions while maintaining air-fuel ratio near stoichiometry in SI mode and constraining the maximum pressure rise rate (MPRR) below 8 bar/CAD in the RCCI mode.

Investigation on combustion characteristics and gas emissions of a high-pressure direct-injection natural gas engine at different combustion modes

In the present study, the potential of natural gas pre-injection, mixing-limited combustion, and slightly premixed combustion modes were evaluated to achieve high thermal efficiency and low nitrogen oxides and carbon monoxide emissions. To this end, a dual direct injection model was established to perform numerical simulations. The obtained results revealed that in the natural gas pre-injection mode, the optimized natural gas pre-injection proportion and injection interval between the end of natural gas pre-injection and the start of diesel injection can significantly reduce carbon monoxide emissions and improve indicated thermal efficiency with a slight increase in nitrogen oxides. In the mixing-limited combustion mode, combustion phasing and indicated thermal efficiency are not sensitive to the variations of the injection interval between diesel and natural gas. Moreover, a larger injection interval between diesel and natural gas is beneficial to reduce carbon monoxide. In the slightly premixed combustion mode, as the injection interval between diesel and natural gas decreases, combustion phasing delays, carbon monoxide emissions reduce, and nitrogen oxides emissions increase first and then decrease. Advancing the start of natural gas injection increases maximum pressure rise rate and nitrogen oxides in both natural gas mixing-limited combustion and slightly premixed combustion modes but decreases carbon monoxide dramatically. The natural gas mixing-limited combustion mode has more potential to meet carbon monoxide limits imposed by the Euro VII standard with no need for extra after-treatment devices while improving thermal efficiency.

Effects of split injection strategy on combustion stability and GHG emissions characteristics of natural gas/diesel RCCI engine under high load

Natural gas/diesel RCCI mode is considered as a high-efficiency clean low-temperature combustion strategy with great application prospects. In order to solve the problem that RCCI engines are prone to knock combustion under high load, the effects of diesel start of main-injection (SOImain), start of pilot-injection (SOIpilot) and pilot-injection quantity (PIQ) on in-cylinder combustion and pollutant emissions of RCCI engine were systematically investigated. Results show that the advance of SOImain effectively reduces CO, HC, soot and CH4 emissions of RCCI engine, but increases knock tendency and NOx emissions. Split injection strategy makes combustion exothermic of RCCI mode present two-stage heat release phenomenon. When SOIpilot is advanced from −15°CA ATDC to −27°CA ATDC, the IMEP and combustion pressure peak increase, the knock tendency significantly decreases, and CO, HC, soot and CH4 emissions are reduced by 55.6%, 43.1%, 28.8% and 39.1% respectively. With the increase of PIQ, the in-cylinder combustion of RCCI engine gradually changes from single-stage to two-stage heat release, the ignition delay is shortened, and the knock tendency is enhanced. Compared with single injection strategy, split injection strategy can simultaneously reduce HC, CO and greenhouse gas emissions, as well as maximum pressure oscillation amplitude and pressure rise rate in RCCI mode.

Effects of operating parameters on combustion and soot emissions in a pilot ignited HPDI natural gas engine for different combustion modes

In this paper, a comprehensive numerical study of the combustion and emission characteristics of a direct injection natural gas engine operating at the high load condition was presented. First, two combustion modes, natural gas mixing-limited combustion (NMLC) and natural gas slightly premixed combustion (NSPC), were defined separately. Subsequently, the potential of combustion chamber type, spray angle of natural gas (SAN), diesel injection pressure (DIP), and natural gas injection pressure (NIP) to achieve high thermal efficiency and low soot emissions are evaluated in both NMLC and NSPC modes. The results showed that in both NMLC and NSPC modes, the straight-sided combustion chamber (SSCC) has more potential to improve the indicated thermal efficiency (ITE) and reduce soot emissions. In NMLC mode, an appropriate increase in SAN can promote the development of vortex at the bowl bottom and improve the stratification state of concentration gradient, thus enhancing ITE, inhibiting the production of pyrene (A4) and acetylene (C2H2), and reducing soot emissions. However, an excessive increase in SAN will lead to fuel accumulation, thus deteriorating soot emissions. In NSPC mode, when SAN increases to 15°, ITE reaches the maximum. Meanwhile, the production of soot precursors (A4 and C2H2) reduces, thus soot emissions reach an extremely low level. However, when SAN exceeds 15°, soot emissions increase rapidly along with the rising SAN. In both combustion modes, when NIP is low, increasing DIP can significantly reduce soot emissions. In NMLC mode, the increase of NIP is more effective in enhancing ITE and inhibiting soot formation. In NSPC mode, when NIP reaches 30 MPa, the maximum pressure rise rate (MPRR) exceeds the limit (1.5 MPa/°CA). When NIP exceeds 30 MPa, ITE begins to decrease. Therefore, NIP should be controlled within 30 MPa for NSPC mode.

Research on destructive knock combustion mechanism of heavy-duty diesel engine at low temperatures

ABSTRACT To clarify the mechanism of destructive knock combustion and piston ablation in heavy-duty diesel engines operating at low temperatures, CONVERGE simulation and wall temperature measurement were performed. The results show that as the initial temperature (intake valve closing instant) decreases from 380K to 307K, the spray wet-wall ratio increases from 12.8% to 22.2%. The fuel film evaporates slowly at low temperature before the hot flame, so the ignition is seriously delayed until the fuel injection ends, and the free-jet autoignition shifts to wall-attached combustion. However, the fuel film evaporation reverses after hot flame, and the maximum evaporation rate at 307K is about 54 times that at 380K. The wall temperature rises sharply to 350-450°C during wall-attached combustion. As the initial temperature decreases, the maximum pressure rise rate increases from 0.9MPa/°CA to 8.3MPa/°CA, and the pressure waves repeatedly oscillate along the end-center-end path in the cylinder. The highest pressure at the monitoring point is nearly an order of magnitude higher than the average, and the oscillation amplitude is as high as 6-10MPa, which far exceeds the failure threshold. The piston whose strength has been greatly reduced after thermal shock quickly undergoes ablation damage under strong pressure shock.

Dynamics of Pressure Variation in Closed Vessel Explosions of Diluted Fuel/Oxidant Mixtures

Nitrous oxide is widely used as oxidizer or nitriding agent in numerous industrial activities such as production of adipic acid and caprolactam and even for production of some semiconductors. Further, it is used as an additive in order to increase the power output of engines, and as an oxidizer in propulsion systems of rockets, because it has a large heat of formation (+81.6 kJ mol−1). N2O is highly exothermic, and during its decomposition a supplementary heat amount is released, so it needs special handling conditions. The combustion of fuels in nitrous oxide atmosphere can lead to high unstable and turbulent deflagrations that speedily self-accelerate and therefore a deflagration can change to a detonation. The peak explosion pressure and the maximum rate of pressure rise of explosions in confined spaces are key safety parameters to evaluate the hazard of processes running in closed vessels and for design of enclosures able to withstand explosions or of their vents used as relief devices. The present study reports some major explosion parameters such as the maximum (peak) explosion pressures pmax, explosion times θmax, maximum rates of pressure rise (dp/dt)max and severity factors KG for ethylene-nitrous oxide mixtures (lean and stoichiometric) diluted with various amounts of N2, at various initial pressures (p0 = 0.50–1.50 bar), in experiments performed in a spherical vessel centrally ignited by inductive-capacitive electric sparks. The influence of the initial pressure and composition on pmax, θmax and (dp/dt)max is discussed. The data are compared with similar values referring to ethylene-air mixtures measured in the same initial conditions. It was found that at identical C/O ratios with ethylene-air, ethylene-N2O-N2 mixtures develop higher explosion pressures and higher rates of pressure rise, due to the exothermic dissociation of N2O under flame conditions.

Inhaled Epoprostenol and Milrinone Effect on Right Ventricular Pressure Waveform Monitoring

BackgroundPulmonary hypertension (PH) and right ventricular (RV) dysfunction are major complications in cardiac surgery. This study aimed to evaluate the change in RV pressure waveform in patients receiving a combination of inhaled epoprostenol and inhaled milrinone (iE&iM) before cardiopulmonary bypass (CPB) and to assess the safety of this approach with a matched case-control group. MethodsA prospective single-centre cohort study of adult patients undergoing cardiac surgery administered iE&iM through an ultrasonic mesh nebulizer. RV pressure waveform monitoring was obtained by continuously transducing the RV port of the pulmonary artery (PA) catheter. ResultsThe final analysis included 26 patients receiving iE&iM. There was a significant drop in mean PA pressure (MPAP) (–4.8 ± 8.7, P = 0.010), systolic PA pressure (SPAP) (–8.2 ± 12.8, P = 0.003), RV end-diastolic pressure (RVEDP) (–2.1 ± 2.8, P < 0.001) and RV diastolic pressure gradient (RVDPG) (–1.7 ± 1.4, P < 0.001) after 17 ± 9 minutes of iE&iM administration. Patients also had a significant increase in RV outflow tract (RVOT) gradient (3.7 ± 4.7, P < 0.001), RV maximal rate of pressure rise during early systole (dP/dt max) (68.3 ± 144.7, P = 0.024), and left ventricular (LV) dP/dt max (66.4 ± 90.1, P < 0.001). Change in RVOT gradient was only observed in those with a positive pulmonary vasodilator response to treatment. Treatment with iE&iM did not present adverse effects when compared with a matched case-control group. ConclusionsCoadministration of iE&iM in cardiac surgery patients presenting with PH or signs of RV dysfunction is a safe and effective treatment approach in improving RV function. Appearance of a transient increase in RVOT gradient after iE&iM could be useful to predict response to treatment.

Effect of ignition position on the combustion instability of premixed methane-air in a semiopen duct

Experiments were conducted in a semiopen chamber to investigate the combustion instabilities of methane-air mixtures. The effect of ignition position (IP for short, i.e., the distance between ignition source and the closed end of a channel) on the characteristics of the pressure waveform of premixed stoichiometric methane-air mixture combustion is investigated in detail. The results reveal that the pressure waveforms demonstrate periodic oscillations when the ignition position is at the half-part of the duct on the side of the open end. The maximum pressure for the oscillating cases is 2.38 times that for the nonoscillating cases, and the maximum rate of pressure rise for the oscillating cases is one order of magnitude higher than that for the nonoscillating cases. The instant of burnout of the methane-air mixture escaping earlier from the open end coincides with the onset of the periodic oscillation. Then, the pressure oscillation is amplified with the exponentially growing amplitude through the flame-pressure interaction. The oscillation amplitude increases as the ignition position shifts toward the open end of the duct. The flame trajectory shows an intimate link with the pressure profile. The oscillating flame velocity precedes the oscillating pressure signal by a 180° phase shift. It is corroborated that the oscillation period depends on the length of the unburnt gas column located between the closed-end and the flame front, irrespective of the ignition position. The pressure oscillation amplitude is a linear function of the frequency. The growth rate of pressure oscillation is calculated through the velocity coupling mechanism. It is shown that the experimental growth rate is compatible with the calculated growth rate for premixed methane combustion. Front ignition produces the highest acoustic energy and thus a higher maximum combustion pressure.

Effect of diesel/PODE/ethanol blends coupled pilot injection strategy on combustion and emissions of a heavy duty diesel engine

Ethanol has limited solubility in diesel. Polyoxymethylene dimethyl ethers (PODE) can enhance the miscibility of ethanol/diesel blends. The application of pilot injection strategy can improve combustion noise and NOx emissions. Thus, the effects of different diesel/PODE/ethanol blends coupled various pilot injection strategies on the combustion, performance and emissions were conducted in a six-cylinder heavy duty diesel engine. As renewable alternative fuel, PODE has the characteristics of high cetane number, high oxygen content and no CC bond, while ethanol has the characteristics of high volatility and high oxygen content. The results show that the significant differences in heat release rate (HRR) and maximum pressure rise rate (MPRR) among DP20, DPE5, DPE10 and DPE15 can be reduced by using the pilot injection, in that the differences in HRR timing and peak value of HRR are weakened. Both the brake and indicated thermal efficiency of blends can be improved by appropriately optimizing the pilot strategy, when compared with the case of single injection. The thermal efficiency of blends is more sensitive to the pilot injection quantity, while the CO and HC emissions are more sensitive to the pilot-main interval. For single injection, blending ethanol into PODE/diesel blends causes adverse effects of increasing hazardous gas emissions, while optimizing pilot injection strategy can reduce the hazardous gas emissions of the blends to the best level of diesel and significantly reduce soot emissions when compared to diesel.

Explosion Flame and Pressure Characteristics of Nonstick Coal Dust and the Inhibition of Explosion Suppressants

Nonstick coal is widely distributed in the world and is an important resource for human beings. The explosion characteristics and explosion suppression of nonstick coal dust are increasingly concerning. In this paper, the flame and pressure characteristics of a nonstick coal dust explosion are studied, and the suppression effect of SiO2, KCl, and NH4H2PO4 on the explosion is analyzed. It is concluded that the maximum propagation distance of a nonstick coal dust explosion flame is 0.59 m, the maximum pressure is 0.63 MPa, and the maximum pressure rise rate is 40.79 MPa/s. The explosion suppression effect of SiO2 is worse than that of KCl, but the inhibition effect of NH4H2PO4 is the best among the three kinds of explosion suppressants. When the mass percentage of NH4H2PO4 dust mixed with coal dust is 70%, the coal dust explosion is completely suppressed. It absorbs a certain amount of heat to promote the chemical reaction, which plays a certain role in controlling the explosion process, and its explosion suppression mechanism includes both physical and chemical explosion suppression.

Laminar combustion characteristics of methane/methanol/air mixtures: Experimental and kinetic investigations

Methanol has been studied to solve the problems of insufficient combustion and unstable operation of natural gas engines. To explore the influence of methanol addition on natural gas/air mixture, the laminar combustion characteristics of stoichiometric methane/methanol/air mixture with methanol volume fractions of 0–100% are measured in a constant volume combustion chamber under the initial pressures of 1–4 bar and initial temperatures of 353–393 K. The experimental results show that the laminar combustion characteristics are linearly enhanced by methanol addition. When the methanol volume fraction varies from 0% to 100% at 393 K and 4 bar, the change rates are 11.7%, 120.4%, - 28.1% and 61.7% for combustion peak pressure, maximum pressure rise rate, combustion duration and laminar burning velocity (LBV) respectively. At high pressure, the influence of methanol addition is enhanced. Chemical kinetics analysis shows that CH2OH, the intermediate product of methanol oxidation, generates HO2 through R134: CH2OH + O2<=>CH2O + HO2, which contributes from 14% to 56% to the generation of HO2, so that HO2 replaces part of the O2 to participate the reaction with H, resulting in the transformation of part of R1: H + O2<=>OH + O to R10: HO2+H<=>2OH, thereby generating more OH and promoting the reaction.

Performance evaluation of artificial neural networks for a fish oil biodiesel fueled diesel engine: Paying a pathway to sustainable energy in environmental progress

AbstractThe purpose of this study is to develop a neural networks model to predict the performance monitoring of the compression ignition engine at various injection timings (21°, 24°, 27°bTDC) using fish oil biodiesel thereby increasing the sustainability of the biodiesel and leading to greener environment. The influence of the injection timing on the engine performance, emission, and combustion are observed in a four‐stroke single cylinder, constant speed, direct injection with a rated output of 4.4 kW using fish oil biodiesel blended with diesel. Feed forward back propagation, Elman feed forward, and Cascade back propagation neural networks‐based models are created to predict the parameters like ignition delay, maximum rate of pressure rise, combustion duration, smoke, hydrocarbon, oxides of nitrogen, carbon monoxide, and carbon dioxide, brake thermal efficiency, brake specific fuel consumption, and exhaust gas temperature. Scaled conjugate gradient and Levenberg–Marquardt have been used as training functions. The predictive capability of the models is compared with each other. It is observed that Elman feed forward with trainlm is the best model with the correlation coefficient is 0.9–1 and low root mean square error. The developed artificial neural network (ANN) predicts the engine parameters with the acceptable correlation limits and proves the efficiency and precision of the model which significantly reduces the time consumption and cost incurred in real time application. Hence by using limited experimental investigations the more accurate engine performance and emissions can be determined for wider engine operating conditions using Elman feed forward ANN.

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.

Experimental investigation of the control strategy of high load extension under iso-butanol/biodiesel dual-fuel intelligent charge compression ignition (ICCI) mode

Advanced combustion modes have shown the great advantages to achieve high thermal efficiency and low pollution emissions. However, lack of sufficiently control over combustion phasing of heat release under high and ultra-high engine load limits the commercial application. In this paper, an experimental investigation had been conducted to explore the control strategy under iso-butanol/biodiesel dual-fuel intelligent charge compression ignition (ICCI) mode for achieving the high engine load extension. The criteria is used to identify clean combustion under high load expansion, which the indicated thermal efficiency is 45% or higher, and nitrogen oxides (NOx) emissions should be below 400 ppm. The results show that stable and controllable ICCI operation is obtained under high and ultra-high engine load. An iso-butanol single direct injection in the intake stroke, biodiesel double direct injection strategy in the compression stroke and near top dead center, respectively, offers a very competitive pathway to expand the engine load with clean and highly efficient combustion, in which the maximum indicated thermal efficiency reaches 49.9% and NOx emissions below 100 ppm at the indicated mean effective pressure (IMEP) of 12 bar, and the maximum engine load reaches 18 bar IMEP (96% engine load). At higher engine load, lower iso-butanol energy ratio is used to reduce the in-cylinder pressure and maximum pressure rise rate, while punishes the engine thermal efficiency and emissions. With the iso-butanol energy ratio increase, the lower in-cylinder reactivity leads to the increase of incomplete combustion products. In addition, the exhaust gas recirculation (EGR) is essential on the reduction of NOx emissions, and the second biodiesel injection duration is increased with the engine load increase for the purpose of the load expansion.

Utilization of multiwalled carbon nanotubes (MWCNT) additive in HCCI engine to widen operating range

Homogenous charge compression ignition (HCCI) combustion mode is a promising technology for the future of internal combustion engines because of its high thermal efficiency. However, HCCI engines have limited stable operating range which is a major drawback. Nanoparticles usage as fuel additive provides improvement of combustion characteristics of internal combustion engines. The objective of this study is to enlarge operating range of HCCI engine. For this purpose, the effects of multiwalled carbon nanotubes (MWCNT) on combustion characteristics of an HCCI engine were scrutinized. The effects of MWCNT on engine operating range, combustion parameters, and HC and CO emissions were determined. The maximum operating range was obtained with 75 % n-heptane, 25 % ethanol, and 100 ppm MWCNT mixture. Compared to 75 % n-heptane and 25 % ethanol mixture, 75 % n-heptane, 25 % ethanol, and 100 ppm MWCNT mixture increased the operating range of engine 112 %. Furthermore, in-cylinder pressure, heat release rate, indicated thermal efficiency, and maximum pressure rise rate were increased with use of MWCNT additive. Start of combustion and 50 % heat release location was shifted to earlier crank angles. Combustion duration was shortened. HC and CO emissions were also decreased.

Laminar burning characteristics of bio-aviation fuel candidate derived from lignocellulosic biomass

This study investigated the laminar burning characteristics of bio-aviation fuel candidate produced from corn stover lignin via catalytic hydrodeoxygenation (HDO). The experiments were conducted at equivalence ratios of 0.7–1.4, initial pressures of 1 bar, 2 bar, and 4 bar, and initial temperatures of 443 K and 473 K. The laminar burning velocity (LBV), explosion pressure, maximum pressure-rise rate, and combustion duration were studied. The LBV was studied using the constant volume (CVM) and constant pressure (CPM) methods. The CVM results were significantly higher than that of CPM in the presence of cellular flame. In other cases, the deviations of both were within 10 %. The analysis indicated that the LBV of the bio-aviation fuel candidate at certain equivalence ratios was lower than that of Jet A-1, RP-3, and n-decane. However, the LBV of the bio-aviation fuel candidate was greater than that of n-decane in fuel rich mixtures. A 12-term power-law correlation was determined to quantify the relationship between the LBV of the bio-aviation fuel candidate and the equivalence ratio, initial temperature, and initial pressure. The maximum deviation between the experimental data and the correlation was 11.85 %, and the average deviation was 2.95 %. Finally, the effects of the initial conditions on the explosion characteristics of the bio-aviation fuel candidate were analyzed. The explosion pressure, maximum pressure-rise rate, and deflagration index were linearly and positively correlated with the initial pressure; however, the latter two were insensitive to the initial temperature. Furthermore, a quantitative correlation between the explosion characteristics and the equivalence ratio and initial pressure was determined.

On the smoothing explosion pressure curves using Savitzky-Golay method

This study reports the optimal range of window width of Savitzky–Golay method for smoothing the raw oscillating explosion evolution curves obtained in methane-air mixtures. The experiments were carried out in a closed vessel of 3.375 L at various equivalence ratios (φ=0.8−1.2) and initial pressures (P0=1.0−2.5bar). All experiments were conducted at room temperature (293 K). The optimal range of window width and the corresponding explosion characteristics (the maximum explosion pressure Pmax, maximum pressure rise rate (dp/dt)max and deflagration index KG) of each initial condition were determined. The results show that (dp/dt)max is influenced markedly by the window width, and some similar behaviors (three characteristic segments) of (dp/dt)max-window width curves are found. Besides, the optimal range of window width depends not only on the equivalence ratio but also on the initial pressure, and the representative median of each range shows a downward trend with the initial pressure. And the median is stable at 1251 points when P0 is greater than 2.0 bar at φ=0.8, while it shows a linear decrease at φ=1.0 and φ=1.2, and maybe also tends to a stable value at a higher initial pressure. Furthermore, Pmax, (dp/dt)max and KG corresponding to the optimal range of window width have perfect linear correlations with P0, verifying convincingly the correctness of the range we determined.

Simulation study on effects of EGR ratio and compression ratio on combustion and emission characteristics of PODE/methanol RCCI engine

In order to solve the problems of combustion instability and emission deterioration of reactivity controlled compression ignition (RCCI) engine under high load, the in-cylinder combustion model of polyoxymethylene dimethyl ethers (PODE)/methanol dual-fuel RCCI engine was constructed by CONVERGE software coupling with chemical reaction mechanism, and the influence mechanism of exhaust gas recirculation (EGR) ratio and compression ratio (CR) on engine performance, in-cylinder combustion and emission characteristics of PODE/methanol RCCI mode was systematically studied. Results show that with the increase of EGR ratio, the combustion phase of RCCI mode is gradually delayed, the ignition delay and combustion duration are extended, the CA50 phase is gradually delayed, the combustion temperature decreases, the mixture distribution becomes more uniform, and the combustion process becomes smoother. When the EGR ratio increases from 0 % to 30 %, NOx production is reduced by 47.3 %, ringing intensity (RI) and maximum pressure rise rate (MPRR) decreases by 1.31 MW/m2 and 0.37 MPa/°CA respectively, and brake thermal efficiency (BTE) decreases from 45.45 % to 43.19 %. With the reduction of CR, the combustion start point is gradually postponed, the peak heat release rate and combustion temperature continuously decrease, and both IMEP and BTE show a downward trend. The variation of CR breaks the trade-off relationship between NOx and soot, and improves combustion stability, but it is also limited by the BTE reduction. When the CR decreases from 17.5 to 15.5, NOx and soot production are reduced by 28.58 % and 20.1 %, RI and MPRR are reduced by 1.26 MW/m2 and 0.7 MPa/°CA respectively, and BTE decreases from 45.45 % to 44.52 %. Therefore, the CR of 16.5 is more suitable for stable operation of PODE/methanol dual-fuel RCCI engine at high load.

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.