Maximum Rate Of Pressure Rise Research Articles

Effects of ignition location on the characteristics of dust explosion venting at elevated static activation pressure

The effect of ignition location on the pressure characteristics of vented dust explosion was investigated in a 20 L chamber. For internal pressure, the proportion of the venting mixture with different ignition locations coupled with the wall quenching effect dominated the internal pressure curves. Besides, the maximum pressure rise rate was controlled by the residual amount of the fuel and induced turbulence. For external pressure, the ignition location dominated the delay time of the external explosion and the number of pressure peaks. Furthermore, the generation mechanism of pressure peaks was revealed by external pressure curves together with the visualization of the flow field. Eventually, it was found that both the internal and external maximum pressure with central ignition was larger than rear-end ignition and then the front-end. The corresponding dynamic mechanism was theoretically revealed, and a dimensionless prediction model for venting size and maximum external pressure was established.

In-cylinder pressure profiling for CNG/ethanol enriched biodiesel combustion

The current study takes a comparative approach to analyze the In-Cylinder pressure distributions and their effect on the engine combustion stability for a specific diesel engine when fueled with Mahua biodiesel in split injection mode with low reactive CNG/ethanol through port fuel injection. Variations in injection time, main-pilot energy sharing, and reactivity of the fuel mixture are included in this investigation. The engine’s operational and combustion stability during ethanol/CNG enriched Mahua biodiesel operation has been demonstrated by the coefficient of variance of indicated mean effective pressure and maximum rate of pressure rise, respectively. The minimum value of the stability index of maximum pressure rise rate for CNG-biodiesel & ethanol-biodiesel combustion illustrated a 49.23% & 88.07% reduction compared to baseline diesel operation. The minimum value of COVIMEP for the respective fuel strategies registered 83.49% & 40.27% lower measures than the corresponding baseline diesel operation. This inquiry also examines the variance in emission and performance of the test engine with stability indicators. 13.04% & 34.92% higher thermal efficiency have been reported for ethanol-biodiesel operation under the most stable combustion and operating conditions. Significantly lower particulate matter and carbon monoxide footprints have been reported under CNG-biodiesel operation with higher stability conditions.

Cardioprotective Effects of a Selective c-Jun N-terminal Kinase Inhibitor in a Rat Model of Myocardial Infarction.

Activation of c-Jun N-terminal kinases (JNKs) is involved in myocardial injury, left ventricular remodeling (LV), and heart failure (HF) after myocardial infarction (MI). The aim of this research was to evaluate the effects of a selective JNK inhibitor, 11H-indeno [1,2-b]quinoxalin-11-one oxime (IQ-1), on myocardial injury and acute myocardial ischemia/reperfusion (I/R) in adult male Wistar rats. Intraperitoneal administration of IQ-1 (25 mg/kg daily for 5 days) resulted in a significant decrease in myocardial infarct size on day 5 after MI. On day 60 after MI, a significant (2.6-fold) decrease in LV scar size, a 2.2-fold decrease in the size of the LV cavity, a 2.9-fold decrease in the area of mature connective tissue, and a 1.7-fold decrease in connective tissue in the interventricular septum were observed compared with the control group. The improved contractile function of the heart resulted in a significant (33%) increase in stroke size, a 40% increase in cardiac output, a 12% increase in LV systolic pressure, a 28% increase in the LV maximum rate of pressure rise, a 45% increase in the LV maximum rate of pressure drop, a 29% increase in the contractility index, a 14% increase in aortic pressure, a 2.7-fold decrease in LV end-diastolic pressure, and a 4.2-fold decrease in LV minimum pressure. We conclude that IQ-1 has cardioprotective activity and reduces the severity of HF after MI.

Simulation of combustion process in diesel/butanol dual fuel engine

ABSTRACT To investigate the feasibility of diesel engines with high butanol substitution rate (BSR), the performance and emissions of diesel–butanol dual fuel engines are studied numerically. It i based on a four-cylinder diesel engine, which is modified into a diesel–butanol dual fuel engine with port-injected butanol fuel and direct-injected diesel fuel. The simulation is performed using GT-Power software, and simulation results are validated with the experimental data. The engine speeds are set at 1600, 2300, and 3600 rpm, respectively. The engine load is set at 25%, 50%, and 75% engine load, respectively. The BSR varies from 0% to 80% with an interval of 10%. The results show that, with the increase of BSR, the peak cylinder pressure (PCP), and the maximum pressure rise rate (MPRR) decrease, while the brake mean effective pressure (BMEP) and the indicated thermal efficiency (ITE) increase under various working conditions. Among them, the MPRR increases by 9%–12%, while the ITE increases by 6%–7%. In terms of emissions, the nitrogen oxide (NOX) decreases obviously (decrease by 32%–54%), while the carbon monoxide (CO) and the hydrocarbons (HC) decrease slightly (CO: decrease by 4%–10%, HC decrease by 3%–4%).

Experimental study on CO2/CF3I suppression of methane-air explosion and flame propagation

To explore the inhibitory effects of CF3I and CO2 gas on the explosion pressure and flame propagation characteristics of 9.5% methane, a spherical 20 L experimental explosion device was used to study the effect of the gas explosion suppressants on the maximum explosion pressure, maximum explosion pressure rise rate and flame propagation speed of methane. The results indicated that with a gradual increase in the volume fraction of the gas explosion suppressant, the maximum explosion pressure of methane and maximum explosion pressure rise rate gradually decreased, and the time taken to reach the maximum explosion pressure and maximum explosion pressure rise rate was gradually delayed. At the same time, the flame propagation speed gradually decreased. Additionally, the time taken for the flame to reach the edge of the window and the time taken for a crack as well as a cellular structure to appear on the flame surface was gradually delayed. The fluid dynamics uncertainty was suppressed. The explosion pressure and flame propagation processes were markedly suppressed, but the flame buoyancy instability was gradually enhanced. By comparing the effects of the two gas explosion suppressants on the pressure and flame propagation characteristics, it was found that at the same volume fraction, trifluoroiodomethane was significantly better than carbon dioxide in suppressing the explosion of methane. By comparing the reduction rates of the characteristic methane explosion parameters at a volume fraction of 9.5%, it was observed that the inhibitory effect of 4% trifluoroiodomethane on the maximum explosion pressure was approximately 4.6 times that of the same amount of carbon dioxide, and the inhibitory effect of 4% trifluoroiodomethane on the maximum explosion pressure rise rate and flame propagation speed was approximately 2.7 times that of the same amount of carbon dioxide. The addition of 0.5%–1.5% trifluoromethane to 4% and 8% carbon dioxide can improve the explosion suppression efficiency of carbon dioxide. This enhancing phenomenon is a comprehensive manifestation of the oxygen-decreasing effect of carbon dioxide and the trifluoroiodomethane-related endothermic effect and reduction in key free radicals.

Explosive properties of selected aerosols determined in a spherical 5-L test chamber

Combustible liquids in the form of aerosols are important for many industrial processes. Therefore the problem of explosion hazards posed by the aerosols becomes increasingly more prominent. To correctly assess the explosion risk and fulfil the requirements of the ATEX directive, it is necessary to obtain information regarding the flammable and explosive properties of the aerosols. Unlike in the case of gases and dusts, no standard procedures aimed at obtaining quantitative information of this type exist. Factors that influence the explosion dynamics of aerosols include: concentration, droplet size, temperature etc. Some of these factors are strongly dependent on the aerosol generation methods. A prototype apparatus was designed and constructed to address that dependence. The apparatus was used in an attempt to determine the basic explosion parameters of liquid flammable aerosols. The device consisted of a 5-L spherical vessel equipped with a pump-injection system that generated aerosols as well as a spark ignition source. A wide variety of injection settings were tested to select the most suitable conditions over a broad range of concentrations and fluid properties. A measurement procedure was developed for operating the device. Prototype tests were carried out with fluids commonly used in industry: isopropanol and kerosene. The tests demonstrated the significant influence of the vessel wall temperature on the result accuracy. Correct temperature control made it possible to obtain relationships between the aerosol concentration and the following explosion parameters: maximum explosion pressure and maximum rate of pressure rise.

Effects of hydrogen mixing ratio on combustion and emissions of natural gas‐diesel dual fuel engine with high natural gas substitution rate

AbstractIn order to explore the feasibility of natural gas (NG)/diesel dual‐fuel engine with high NG substitution rate under medium and low load, the effects of hydrogen (H2) on the performance and emissions of the engine are studied numerically. The baseline engine is a four‐cylinder turbocharged diesel engine, which is modified into a diesel‐Natural Gas‐Hydrogen ternary fuels engine with port‐injected H2 and NG fuels and direct‐injected diesel fuel. The simulation is performed using GT‐Power software, and numerical results are validated with the experimental data. The percentage of diesel fuel is set at 10% and 20% (by energy). The engine speed decreases from high speed to medium speed and finally to low speed. The engine load decreases from medium load to low load. The H2 mixing ratio increases from 10% to 50%. The results show that, with the increase of H2 mixing ratio, the peak cylinder pressure (PCP), the peak cylinder temperature (PCT), the heat release rate (HRR) and the maximum pressure rise rate (MPRR) increase, while the indicated thermal efficiency (ITE) decreases under all working conditions. Among them, the MPRR increases by 4%~13% at medium load and 1%~2% at low load, but it does not exceed 0.6 MPa/ (°) CA. The indicated thermal efficiency decreases by 1%~4% at medium and low load. In terms of emissions, the carbon monoxide (CO) and the hydrocarbons (HC) decrease by 34%~43%, but the nitrogen oxide (NOX) increases by 58%~73%.

Performance optimization of RCCI engines running on landfill gas, propane and hydrogen through the deep neural network and genetic algorithm

The present study is to optimize the performance of the reactivity controlled compression ignition engines taking landfill gas plus propane or hydrogen or a combination of both as low reactivity fuels. A heavy duty, 2.44 L caterpillar 3401E single-cylinder diesel engine is employed for the numerical simulation, and a number of the most effective variables on the engine performance are determined as inputs. The research purposes are to procure the maximum energy efficiency (i.e. the maximum thermodynamics first and second law efficiencies, and the minimum indicated specific fuel consumption), and to fulfill the Euro VI engine emissions standards (i.e. CO, UHC, and NOX maximum emissions 1.5, 0.13, and 0.4 gr/kW-hr, respectively). The maximum peak pressure and peak pressure rise rate are restricted to 150 bar and 10 bar/crank angle deg., respectively. The deep neural networks are utilized to obtain the engine mathematical model and the genetic algorithms are used to attain the intended optimization. Based on the outcomes, injecting a combination of propane and hydrogen to the premixed charge by 3.4 and 6.6 % by volume, respectively, and adopting an engine equivalence ratio of 0.31, an intake pressure of 1.983 bar, and a diesel fuel injection timing of about 75 deg. before the top dead center provide the maximum performance for the considered engine. In the optimized state, a 6.6 % hydrogen by volume takes 2.5 % of the total fuels energy. This research has proven that numerical modeling in combination with deep neural networks and genetic algorithms is an effective methodology to optimize the performance of the reactivity controlled compression ignition engines. Moreover, a dimensional analysis made shows the dimensionless peak pressure is function of the dimensionless engine heat release and the ratio of the engine cumulative heat release to the primary inlet mixture flow work. In the optimized case, the dimensionless ratio of cumulative heat release to the inlet flow work of fluid is 11.5.

The study of ignition and emission characteristics of hydrogen-additive hydro-processed renewable diesel

This study was conducted to understand the effects of hydrogen (H2) addition on the combustion and emission characteristics of hydro-processed renewable diesel. Experiments were performed in a constant volume combustion chamber (CVCC) at varying H2 concentrations (0%, 5%, and 10% (by vol.)) relative to air (100%, 95%, and 90% (by vol.)), initial temperatures (Tini) of 600, 650 and 700 K, equivalence ratios (φ) of 0.5, 1.0, and 1.5 and a fixed initial pressure (Pini) of 10 bar. Overall, HRD has lower ignition delay (ID) and total ID. However, H2 addition to HRD delayed the fuel's auto-ignition due to excess H2 oxidation (H2+OHH2O + H) reaction taking place, which turns the chain reactions from branching to propagation, resulting from increasing in ID. Moreover, increasing of H2 concentrations enhanced the maximum pressure rise (Pmax) and heat release rate (HRR), whereas carbon dioxide (CO2) and unburned hydrocarbon (HC) were decreased due to the higher magnitude of the lower heating value of H2 than that of pure HRD. Since H2 itself is a carbon-free molecule, the carbon content of the fuel is reduced. H2 has the characteristics of fast combustion, resulting in a more flammable and complete mixture, which also makes HC emissions to become lower. However, the higher energy density of H2 significantly raises the combustion temperature, and subsequent nitrogen oxides (NOx) were increased. The kinetic modeling predictions revealed that the IDs for HRD-H2 were elongated due to the increased hydroperoxyl (HO2) and hydrogen peroxide (H2O2) mole fractions which led to improved stability.

Combined effect of multi‐injection scheme, injector nozzle bore, and biodiesel blends on combustion and performance characteristics of diesel engine

AbstractMany researchers have conducted extensive experimental and numerical studies to explore the influences of multiple types of fuels. The high demand of energy in the world has led to the growing crisis and depletion of fossil fuels. Therefore, the researchers have focused on investigating renewable energy sources like biodiesel with the aim of suggesting, which energy is more friendly to the environment. Biodiesel has specifications for using it as an alternative fuel to traditional fossil fuels. Whereas, the use of biodiesel fuel in the original design of Diesel engine can emit a higher percentage of nitrogen oxides (NOx). Therefore, to reduce the harmful emissions of the fuel, the injection schemes and injector nozzle bore (INB) of the engine were modified. The present research combines the effect of the nozzle hole diameters and split injection scheme on the performance and combustion parameters of compression ignition (CI) engine was investigated. The engine was fueled with diesel blended of different proportions (Sp20, Sp40, Sp60, and Sp100) of spirulina biodiesel to prove the suitability of this blend as an alternative fuel. The injector nozzle has three injection holes, and the diameter of the three modified holes of the nozzle is changing (from 0.20 to 0.28 mm, step 0.02 mm) along with two types of scheme injection (double and triple). Furthermore, the influence of the direct injection Diesel‐RK model, single‐cylinder, four‐stroke engine; constant compression ratio (17.5:1), engine speed (1500 rpm), and naturally aspired engine at full load condition are studied. A comparison of the present simulation is compared with published results to validate the present simulation model for conventional baseline Diesel for validation. The simulation was done to investigate and present a comparative study with the conventional baseline Diesel engine. The double injection scheme shows a decrease by 1.8%, 1.7%, and 1.9% for parameters of peak cylinder pressure (PCP), peak cylinder temperature (PCT), and maximum rate of pressure rise, respectively. Whereas, the specific fuel consumption (SFC) and break thermal efficiency are increased by 8.7% and 9.33%, respectively. The results showed a reduction by 2.1%, 20.5%, 22.1%, and 3.2% in PCP, PCT, maximum rate of pressure rise, and break thermal efficiency, respectively. Moreover, the SFC is increased by 3.1% with the modified INB 0.28 (mm).

Numerical Optimization of Spray-Guided Spark Assistance for Cold Idle Operation in a Heavy-Duty Gasoline Compression Ignition Engine

This article describes the results of a response surface model (RSM)-based numerical optimization campaign for spray-guided spark assistance at cold operations in a heavy-duty gasoline compression ignition (GCI) engine. On the basis of an earlier work on spark-assisted GCI cold combustion, a space-filling design of experiments (DoE) method was first undertaken to investigate a multitude of hardware design variables and engine operating parameters. The main design variables included the number of injector nozzles, fuel split quantities and injection timings, and spark timing. The objective variables were engine combustion efficiency (ŋc), maximum pressure rise rate (MPRR), and engine-out nitrogen oxide (NOx) emissions. A total of 150 design candidates were automatically generated using the Sobol sequence method provided by the commercial software package, CAESES. Then, closed-cycle computational fluid dynamic (CFD) spark-assisted GCI simulations under cold idling operations were performed. The outcomes from the CFD-DoE design campaign were utilized to construct high-fidelity RSMs that allowed for further design optimization of the spark plug- and fuel injector-related design variables, along with fuel injection strategy parameters. A merit function with respect to objective variables was formulated with an appropriate weight assignment on each objective variable. Finally, the best design candidate was identified from the RSM-based optimization process and further validated in the CFD analysis. The best design candidate showed the potential to significantly improve combustion efficiency (ŋc > 90%) over the baseline at cold idle while satisfying MPRR and NOx emissions constraints (MPRR < 5 bar/CAD and NOx < 4.5 g/kWh).

Experimental investigation and Artificial Neural Network modelling of combustion pressure parameters of dual spark plug SI engine

Shortages of petroleum-based fuels due to their rapid consumption rate and their environmental degradation motivates researchers to develop new technologies for the efficient use of petroleum-based fuels as well as the use of environmentally friendly alternate biofuels. Ethanol is one of the promising alternative biofuels for spark ignition (SI) engines. Currently, the Indian union Government aims to mix 20% ethanol by 2030. Therefore, extensive research studies are needed to determine the combustion stability of E20 blend. The purpose of this study was to investigate the combustion pressure fluctuations is dual plug SI engine using ethanol-gasoline blends and to develop Artificial neural network model using back propagation algorithm for the prediction of these fluctuations. The fluctuations of Indicated mean effective pressure (IMEP), maximum cylinder pressure and maximum rate of pressure rise has been measured by conducting experiment in a dual spark plug SI engine under different compression ratios and spark ignition timings using E5, E10, E15 and E20. Then, these experimental data’s have been used for training and testing of BP model to predict the combustion pressure parameters. The % load, blend ratio, compression ratio and spark timings were used as the input parameters whereas IMEP, maximum cylinder pressure and maximum rate of pressure rise were used as the output parameters of the model. The experimental results showed that E20 achieved maximum average IMEP and minimum COVIMEP at a compression ratio of 10:1 and ignition timings of 24° bTDC. The modelling results showed that BP model is capable of predicting the combustion pressure fluctuations with good accuracy.

Cyclic Combustion Variability of Dimethyl-Ether-Fueled Agricultural Tractor Engine

Abstract Combustion in dimethyl-ether (DME)-fueled engines needs to be assessed carefully for its widespread acceptability from a drivability viewpoint. Since the test engine used in an off-highway segment, it was tested in a steady-state cycle for engine performance, combustion, emissions, and their cyclic variations, which were the only parameters to assess the drivability. This study investigated and analyzed the cyclic variations of a 100% DME-fueled engine equipped with modified mechanical fuel injection equipment. It was compared with baseline diesel to understand its positive and negative aspects. Experiments were conducted at different engine speeds (1200,1600, and 2000 rpm) and loads (No Load, 1.29, 2.59, 3.88, 5.18, and 6.47 bar brake mean effective pressure (BMEP)) . In-cylinder pressure was recorded for 250 consecutive engine cycles, and many combustion parameters were comparatively analyzed for diesel and DME fuelings. The coefficient of variation (COV) of maximum in-cylinder pressure (Pmax) was lower for DME than diesel at 1600 rpm and comparable at the other remaining engine speeds (1200 and 2000 rpm). Variations in COV of Pmax were higher at low loads and negligible at high loads for both test fuels. At 2000 rpm, the crank angle positions at which Pmax occurred were distributed in a narrow range for DME, representing higher combustion stability than baseline diesel. Variations in the maximum rate of pressure rise (RoPRmax) were lower for DME at 3.88 and 6.47 bar BMEP, while these were higher at 1.29 bar BMEP than baseline diesel. COV of indicated mean effective pressure (COVIMEP) decreased from lower to higher loads for diesel and DME fueling at 1600 and 2000 rpm engine speeds. The differences in COVIMEP between diesel and DME were negligible at higher loads, representing engine stability similar to baseline diesel. Combustion parameters assessed indicated that DME fueling led to lower cyclic variations than baseline diesel as the engine operated from lower to higher loads. At lower loads, DME fueling showed higher cyclic variations than baseline diesel.

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.