Combustion Pressure Research Articles

Effects of the Fuel Species on the Combustion Pressure in a Two Staged Fueled Scramjet Combustor

Two-staged fuel injection configuration for scramjet combustors has been shown to be effective in distributing heat release in the combustor for preventing the unstart transition of the engine by suppressing peak pressure while increasing the pressure thrust. In this study, the effect of fuel species on combustion characteristics in a two-staged fueled scramjet combustor was investigated. Wall pressure measurements in a two-staged fueled scramjet combustor were conducted in a combustion wind tunnel facility with fuels having different reactivity, such as H2 and CH4. Reynolds-Averaged Navier–Stokes/Large Eddy Simulation (RANS/LES) hybrid simulations were performed to verify the interaction characteristics between the primary and secondary combustion zones for different fuels. The experimental results confirmed that pressure peaks at injections were clearly separated in the hydrogen case, while these interacted with each other in the methane case with a lower reactivity than H2. The RANS/LES Hybrid analysis predicted this effect of fuel reactivity on the pressure distribution, namely, the heat release delay of the first stage fuel caused the interaction with the second stage fuel heat release. The results indicate that the need to design the staged fueled combustor, i.e., the injection stage interval accordingly to the reactivity of the fuel.

Evaluation of the Effect of Natural Gas Enrichment with Hydrogen on Gas Turbine Emissions: Numerical Study Based on Chemical Equilibrium

Decarbonization involves the intensive use of renewable energy to obtain a sustainable energy matrix. Brazil has an electrical matrix strongly anchored in renewable sources, historically in hydraulic energy, and more recently, in solar, photovoltaic, and wind sources. The latter are stochastic and, therefore, have strong restrictions on their insertion into the matrix in a broad and dominant manner. Due to these limitations, excess supply can be used to produce green hydrogen and even methane in a process called methanation (chemical reaction between CO2 and H2). The use of electrical energy from renewable sources for the production of fuels is known in literature as power-to-gas. These fuel vectors (H2 and CH4) can be used directly to generate energy or can be mixed with natural gas to enrich it in terms of energy and potentially reduce emissions. This study evaluates the effect of enriching mixtures of natural gas and hydrogen on CO, CO2, and NOx emissions, considering combustion applications in Gas Turbines. The analyses were numerical and involved the use of a thermodynamic combustion model with chemical equilibrium. The chemical equilibrium model is based on chemical equilibrium constants and assumes that the reactants and products are ideal gases. The volumetric fractions of H2 in the mixture from 0 to 30% and the effect of the combustion pressure were investigated. The pressure was varied according to the application chosen. Gas turbines are part of the combined power cycles, and plants can operate with gas turbines of different pressure ratios according to the model, power, and manufacturer of the Gas Turbine. The analyses focused on medium and large gas turbines, and the chosen pressure range was 12:1 to 24:1.

Experimental Study of Turbulent Premixed Flames of Gas-to-Liquids (GTL) Fuel in a Fan-Stirred Combustion Bomb

This study experimentally investigates the turbulent flame speeds (St) of Gas-to-Liquids (GTL) fuel and a 50/50 blend with diesel across turbulence intensities (u') ranging from 0.5 to 3.0 m/s and equivalence ratios (Φ) from 0.7 to 1.3. Experiments were conducted using a cylindrical fan-stirred combustion bomb at an initial temperature (Ti) of 463 K and atmospheric pressure under near homogeneous and isotropic turbulence (HIT) conditions. A pressure transducer measured the St of the propagating GTL flame. High-speed imaging reveals that changes in flame brightness are associated with variations in flame temperature and soot incandescence. Compared to diesel, stoichiometric GTL and the 50/50 diesel-GTL blend showed peak combustion pressure reductions of 8.9% and 4.9%, respectively. Rich diesel fuel and lean GTL exhibited higher pressure rise rates, flame propagation, and St due to their Lewis numbers (Le) being less than one, enhancing flame-turbulence interaction. At u` of 0.5, 1.5, and 3.0 m/s, St for GTL increased by approximately 3.6%, 5.3%, and 2.8%, respectively, when compared to diesel, with these increases observed at Φ < 1.1. Transition from wrinkled to corrugated flamelets with increasing u` supports models predicting flame stability and potential industrial combustion efficiency improvements. Comparisons with numerical St results using the Zimont Turbulent Flame Speed Closure (Zimont TFC) model showed good agreement at lower (u' = 0.5 m/s) and mid-range (u' = 2.0 m/s) turbulence intensities but discrepancies at higher intensities (u' = 3.0 m/s), highlighting the need to refine numerical models for more accurate predictions across all turbulence levels.

Dual-loop Segmented Piston Trajectory Control of Free Piston Linear Generator based on sliding mode control

Free piston linear generator (FPLG) can be applied as range extender for electrical vehicles to reduce greenhouse gas emissions attributed to its fuel flexibility and ultimate freedom of piston motion. However, FPLG still faces several challenges in control such as misfire and collision due to the eliminate of mechanical crankshaft. To fully utilize the potential of the ultimate freedom of piston motion, this paper presents a novel piston trajectory control strategy which employs the piston trajectory on the entire operation process of FPLG as the control objective. Considering disturbances and high coupling of FPLG, a sliding mode controller is employed to track reference piston trajectory. Additionally, a segmented control strategy is implemented to decouple the control of combustion pressure force and electromagnetic force. In order to ascertain the effectiveness of the proposed controller, a prototype of single-piston FPLG and a corresponding numerical model are constructed. The experimental and simulation results demonstrate the proposed controller shows fast response, precise tracking performance, and good robustness at various reference piston trajectories. Furthermore, the experimental results illustrate that the system can achieve cold start through the seamless transition between operation states and long-term stable operation by the controller.

Fragmentation Process and Combustion Performance of the Grain-molded Gun Propellant

Abstract In order to research the impact fragmentation and combustion behavior of the grain-molded gun propellant and guide the design of ammunition charge structures, experiments were conducted using constant-volume gas pressure impact and closed bomb tests. Tests were conducted and results were obtained, including the combustion pressure variation curves of the grain-molded gun propellant as well as its disintegration and fragmentation states under different termination pressures. The study analyzed the impact fragmentation process and the progressive combustion characteristics of the grain-molded gun propellant.. The results show that the combustion of the molded gun propellant does not follow the parallel layer combustion rule; The molded gun propellant exhibits inconsistencies in burning rate and disintegration fragmentation, making it difficult to achieve simultaneous ignition and combustion. Additionally, the molded gun propellant can reduce the gas generation rate during the initial stage of cartridge firing, thereby extending the combustion duration.

Combustion characteristics of Ammonia/Air mixture ignited by flame jet with and without hydrogen injection in Pre-Chamber

Ammonia is one of the important fuels that can promote the achievement of carbon neutrality, but its combustion characteristics are not conducive to its application in engines. Injecting hydrogen in the pre-chamber to form a flame jet to ignite the ammonia/air mixture is a method to improve the combustion of ammonia. This ignition method was investigated with the constant volume combustion chamber, high-speed video camera observation and the main-chamber pressure analysis. The flame behavior and combustion characteristics were compared with those ignited by the ammonia flame jet. Hydrogen flame jet significantly enhanced the combustion of the mixture and extended the lean flammability limit. Under conditions of hydrogen injection, the pressure rise delay and combustion duration became shorter, the average heat release rate became higher, and the combustion process was more stable. The hydrogen flame jet rapidly penetrated the main-chamber and impinged on the lower surface, generating intense turbulence. As a result, the combustion pressure took less time to rise from 10% to 50% than it did to go from 50% to 90%. This was different from the situation without hydrogen injection, where time required for both was similar. The hydrogen flame jet was shuttle-shaped when touching the lower surface owing to the rapid combustion speed of hydrogen, while the ammonia flame jet was spindle-shaped with the flame kernel in the center. The combustion process of the flame jet igniting the mixture exhibited two peaks in the heat release rate, reflecting two combustion stages dominated by the flame jet and flame propagation.

Experimental study on char nitrogen conversion characteristics during char combustion process in pressurized O2/CO2/H2O atmosphere

Pressurized oxy-fuel combustion is an advanced CO₂ capture technology with potential applications in coal-fired power generation. In this study, the conversion behavior of char-nitrogen under pressurized oxy-fuel combustion conditions was investigated using a horizontal furnace across a pressure range of 0.1–1.3 MPa in an O₂/CO₂/H₂O atmosphere. The influences of pressure, gas composition, and residence time on nitrogen conversion were examined, and key factors affecting nitrogen transformation pathways were identified. Results indicated that elevated pressures favored NH₃ formation while inhibiting the formation of NO and NO₂, particularly at pressures above 0.7 MPa. Under pressurized conditions (0.7/1.3 MPa), increasing the O₂/CO₂ ratio further suppressed the conversion of char-N to NO, a contrast to behavior observed at atmospheric pressure. X-ray photoelectron spectroscopy analysis revealed a preferential consumption of nitrogen species, such as pyridinic and pyrrolic nitrogen, with pressurization enhancing the depletion of protonated nitrogen. Furthermore, an increased O₂/CO₂ ratio promoted the conversion of nitrogen oxides and other nitrogenous forms.

Study on the effect and mechanism of EGR on methane/hydrogen pre-ignition caused by cylinder lubricating oil auto-ignition

The Otto-cycle mode Llow-speed two-stroke gas engines are prone to pre-ignition and detonation when the engines run with a low excess air ratio. One of the primary causes of abnormal combustion modes is the auto-ignition of cylinder oil. Implementing Exhaust Gas Recirculation (EGR) technology is recognized as one of the most effective strategies to mitigate abnormal combustions. However, the effects and mechanisms of EGR on pre-ignition caused by cylinder oil auto-ignition still require further investigation. Experimental research is conducted under in-cylinder conditions using a Rapid Compression Machine (RCM). The research delves into the influence of EGR on the pre-ignition of gas fuel premixtures, encompassing EGR gas-methane premixture and EGR gas-hydrogen premixture. Furthermore, the study examines the effects of the components present in the EGR gas, specifically CO2 and H2O for natural gas engines, and H2O for hydrogen engines. The findings suggest that EGR plays a crucial role in delaying the ignition delay time of oil droplets, thereby postponing the onset of pre-ignition. EGR also serves to diminish the flame propagation velocity, leading to a lower maximum combustion pressure. The principle effect of EGR is its diluting nature, with the impact of CO2 standing out prominently. The influence of H2O, while significant, is secondary to that of CO2 in prolonging the ignition delay time of cylinder oil droplets and reducing the maximum combustion pressure. Nevertheless, the slowing of flame propagation velocity exhibits only minor effects under the influence of H2O.

Energy and exergy analysis of pulse detonation combustor and pulse detonation turbine engine cycle

As a kind of pressurized combustion, pulse detonation combustion brings many possibilities for the improvement of aero-engine performance.In this paper, energy and exergy analyses of pulse detonation combustor (PDC) and pulse detonation turbine engine (PDTE) cycles based on unsteady analysisare conducted. A simplified exergy flow model is proposed to describe the exergy flow of PDC under different inlet conditions, and based on this, the exergy efficiency of PDC is compared with that of an isobaric combustion chamber. In addition, the energy and exergy flows of ideal and real PDTE cycles are analyzed, and the cycle thermal and exergy efficiencies under different inlet conditions are obtained. The results show that the exergy efficiency of PDC is higher than that of an isobaric combustion chamber from an inlet pressure ratio of 3–45, but the efficiency improvement decreases from 13.2 % to 7.2 %. The thermal efficiency of the ideal PDTE cycle is higher than that of the Brayton cycle, but the efficiency improvement decreases from 78.2 % to 4.7 %. The irreversible losses in the real process will lead to energy loss during compression and expansion processes in the PDTE cycle, thus reducing its exergy efficiency and thermal efficiency.

Investigation of bioethanol low-carbon fuel for diesel engines under idling conditions: Combustion, engine performance and emissions

In this study, the low idle operation is defined as the engine running at the lowest engine speed with a few slight loads. Idling is necessary for most vehicles, especially for buses and trucks that frequently travel long distances, as drivers often rest inside the vehicle. However, under idling conditions, weak air flow and low air-fuel ratio result in poor air to fuel mixture, ultimately causing incomplete combustion and the production of more harmful exhaust emissions. Bioethanol, as a low-carbon fuel, has great potential for application in diesel engines due to its unique properties. In this research, the influences of different diesel-bioethanol blends (BE0, BE5, BE10, BE15) on combustion and emissions of a diesel engine were investigated under idle conditions. The main results show that there was no phase separation phenomenon even up to 15% bioethanol was directly blended with diesel by volume. And adding bioethanol to diesel had no significant impact on combustion pressure peak, but it postponed the start of combustion (SOC). Surprisingly, the nitrogen oxide (NOx) and smoke were simultaneously decreased by over 52% and 78% with the intervention of bioethanol, respectively.

Exergy Analysis of Gas Turbine Open Cycle with Pressure Gain Combustion Based on Humphrey Cycle

Abstract This paper describes an exergy comparison of the pressure gain combustion (PGC) gas turbine (GT) with conventional GT. PGC has recently emerged as a promising approach to achieve major performance improvements in the current gas turbines operating on the Joule cycle, where the potential for major performance upgrades has nearly plateaued. However, the inherently unsteady and periodic nature of this combustion technology presents challenges in modelling the PGC process and understanding its impact on the cycle. In this work, PGC is represented by a steady-state model of constant volume combustion based on the Humphrey cycle, along with a constant pressure combustion loss model for capturing practical losses. Exergy performance was analysed in terms of exergy destruction for three air-cooled GT cycles with different combustors: a conventional isobaric combustor, an optimistic PGC combustor with no losses and a realistic PGC combustor with losses. Gas turbine cycles were modelled in WTEMP (Web-based Thermo-Economic Modular Program) software, a modular and flexible cycle analysis tool developed by TPG at the University of Genova. Simulations were performed at compressor pressure ratios from 5 to 40 at turbine inlet temperatures of TIT=1300°C and TIT=1700°C, and results were analysed in terms of exergy destruction and exergy efficiency. It was found that a PGC combustor with optimistic losses recovers more exergy than a conventional combustor due to pressure gain. At a cycle pressure ratio of 20 and 1700°C TIT, the PGC combustor with a pressure ratio of 1.35 resulted in an exergy efficiency of 79.6% compared to 77.9% of the Joule combustor. However, with realistic loss from inlet pressure drop and constant pressure combustion in the PGC combustor, the PGC combustor showed higher irreversibility than conventional combustor but the overall benefit on the cycle was retained at low compressor pressure ratios. Moreover, the percentage increase in turbine irreversibility from blade cooling was found to be slightly lower for the PGC cycle as compared to Joule.

A Thermodynamic Study of Pressure Gain Combustion in Combined Cycles

Abstract Gas turbines are internal combustion engines based on the Brayton-Joule cycle with four thermodynamic processes including air compression, constant pressure combustion, gas expansion and heat rejection. Actually, a relevant increase in entropy production is related to the constant pressure combustion, even in the ideal cycle, so alternative combustion solutions, such as the Pressure Gain Combustion (PGC), are worthy of attention. This work aims at investigating PGC potential in gas turbines compared to conventional power plants based on the Brayton-Joule cycle. Both simple cycle and combined cycle operations are considered, focusing on a F-class gas turbine unit for power production. Cycle performance is estimated through a thermodynamic in-house code, where the common calculation scheme has been revised in order to simulate a combustion process occurring with increasing pressure from inlet to outlet of the combustor. A booster compressor is necessarily included in the power system for delivering the cooling air to the first stage blades of the turbine. The results are fully satisfactory as PGC technology really improves the efficiency of the gas turbine expander: in case of a pressure gain of 45%, which is a reasonable value based on literature data, 1.3 to 3.4 percentage points more in gas turbine efficiency have been calculated. Finally, a parametric analysis of expansion efficiency penalties due to supersonic pulsating flows at the first stage of the turbine expander is presented.

Investigation into the impact of acetylene on performance and emission characteristics of a compression ignition engine using a blended biodiesel of ethanol and tamanu oil.

Due to the significant increase in transportation, traditional fossil fuels utilised in internal combustion engines will only be accessible for a limited duration. Additionally, the harmful pollutants produced by these fuels, including CO, NOx, unburned hydrocarbons, smoke, and a small amount of particulate matter, have a severe negative impact on the environment. Although biodiesel proves efficient without necessitating engine modifications, its performance is hindered by its higher viscosity. Consequently, this research aims to enhance performance by introducing acetylene alongside tamanu methyl ester (biodiesel); however, this approach results in elevated NOx levels. To mitigate NOx emissions, a combination of ethanol and biodiesel is employed. This study investigates the performance and emission attributes of Acetylene + TME90E10 as the fuel. The combustion pressure and heat release rate of TME90E10 with 6 lpm, improved by 5.41% and 9.1% than diesel. When compared to regular diesel fuel, the introduction of 6l per minute of acetylene with TME90E10 yields a substantial 24.4% decrease in hydrocarbon (HC) emissions. Furthermore, employing TME90E10 at the same acetylene flow rate demonstrates the lowest carbon monoxide (CO) emissions, registering at 0.07%, in contrast to the 0.13% emissions observed throughout the exhaust cycle when using pure diesel fuel.

Characterizing Aircraft Exhaust Emissions and Impact Factors at Tianjin Binhai International Airport via Open-Path Fourier-Transform Infrared Spectrometer.

The growth of the civil aviation industry has raised concerns about the impact of airport emissions on human health and the environment. The aim of this study was to quantify the emissions of sulfur dioxide (SO2), nitrogen oxides (NOX), and carbon monoxide (CO) from in-service aircraft via open-path Fourier-transform infrared (OP-FTIR) spectroscopy at Tianjin Binhai International Airport. The results suggest that the CO and NOX emission indices (EIs) for five common aircraft/engine combinations exhibited substantial discrepancies from those reported in the International Civil Aviation Organization (ICAO) databank. Notably, during the idling, approach, and take-off phases, the CO EIs exceeded the ICAO's standard values by (11.04 ± 10.34)%, (56.37 ± 18.54)%, and roughly 2-5 times, respectively. By contrast, the NOX EIs were below the standard values by (39.15 ± 5.80)%, (13.57 ± 3.67)%, and (21.22 ± 4.03)% in the same phases, respectively. The CO and NOX EIs increased by 31-41% and decreased by 23-24%, respectively, as the ambient temperature decreased from -3 °C to -13 °C. This was attributed to lower temperatures reducing fuel evaporation, leading to inefficient combustion and increased CO emissions and lowering the combustion temperature and pressure, resulting in reduced NOX emissions. The CO EIs had a positive correlation with humidity (adjusted R2: 0.715-0.837), while the NOX EIs were negatively correlated with humidity (adjusted R2: 0.758-0.859). This study's findings indicate that humidity is a crucial factor impacting aircraft exhaust emissions. Overall, this research will contribute to the development of scientifically informed emission standards and enhanced environmental management practices in the aviation sector.

Spray characteristics and combustion mechanism influence on combustion stability of UDMH/NTO pre-combustor under external excitation

To study the combustion stability of liquid rocket engines with hypergolic propellant more comprehensively, external pressure pulse excitation was applied to the UDMH (unsymmetrical dimethylhydrazine)/NTO (methylhydrazine) pre-combustor. The effects of pressure pulse intensity, spray characteristics (droplet diameter and spray cone angle), and combustion mechanism on combustion stability characteristic frequencies and attenuation characteristics after excitation were investigated. The simulation results show that all operation conditions capture the first three longitudinal frequencies of the pre-combustor, and all factors have a greater impact on frequencies with higher orders. Increasing the pulse intensity and reducing the droplet diameter are not conducive to combustion stability. The influence of the spray cone angle on the combustion stability is not monotonous. The pre-combustor has good stability when the spray cone angle is 70°. Different combustion mechanisms have a significant effect on the results before and after pressure pulses, and considering a more complete combustion process may increase the attenuation time in the pre-combustor. The obtained rules can provide a reference for the design and simulation of hypergolic liquid rocket engines, which is beneficial for predicting and evaluating the combustion stability of liquid rocket engines.

Characterizing the Multiscale Knock Energy of the in-Cylinder Pressure of Compound Combustion Engines Fueled with Dimethyl Ether.

A two-cylinder, direct injection, and four-stroke naturally aspirated diesel engine is reformed to the compound combustion engine fueled with dimethyl ether. The wavelet energy spectra of the in-cylinder pressure with normal combustion and knocking combustion in a compound combustion engine are experimentally studied. The effects of the port fuel quantity, engine load, and engine speed on them are analyzed. The multiscale knock energy characteristics of the in-cylinder pressure are investigated based on wavelet energy and the Shannon entropy-energy ratio. The result shows that the in-cylinder pressure oscillation tends to be violent with the increase of port fuel quantity, the peak in-cylinder pressure increases, and its crank angle phase advances. With the increase in port fuel quantity, the wavelet energy of high-frequency detail signals d1, d2, and d3 obtained from wavelet decomposition all increases and the Shannon entropy-energy ratio decreases. The high-frequency detail signal d1 is more sensitive than the other detail signals. The frequency band of 5-10 kHz is the knock characteristic frequency band. The energy of the detail signal d1 increases significantly during knocking combustion, and the oscillation range enlarges and moves forward. The wavelet energy of detail signal d1 is the largest, and the Shannon entropy-energy ratio is the smallest at different brake mean effective pressures and different engine speeds. The effect of brake mean effective pressure and engine speed on the values is not obvious, and the port fuel quantity is the main factor.

The decoupled effect of oxidizer mass flux and combustion pressure on turbulent combustion characteristics of finite-length solid fuel

Combustion pressure and oxidizer mass flux are key factors influencing the performance of hybrid rocket motors. In the present work, the decoupled effects of oxidizer mass flux and combustion pressure on turbulent combustion characteristics were investigated. First, a finite-length combustion theory of fuel grains was developed to identify the main sensitive parameters, including flame structure and the recirculation zone, which affect the combustion of solid fuel. Then, a two-dimensional transient numerical model, based on the coupling characteristics of the heat transfer process in solid fuel grains and dynamic combustion flow, was developed and validated through fire experiments under a wide range of inflow conditions. A quantitative analysis was conducted to assess the impact of flame structure and the recirculation zone on the dynamic combustion characteristics of finite-length solid fuel. The results showed that the fuel characteristic temperatures of the front and central parts are negatively correlated with flame height, while the characteristic temperature of the rear part is positively correlated with the recirculation zone temperature. Both the mass flow rate and combustion pressure are negatively correlated with flame height and positively correlated with the temperature of the recirculation zone. Compared to combustion pressure, the influence of mass flow rate is more significant. The transient processes of the solid fuel regression rate under different inflow conditions exhibit a consistent tendency: an increase in mass flow flux and combustion pressure results in faster attainment of peak regression rate and stabilization.

Experimental and modeling studies on char combustion under pressurized O2/H2O conditions

The desorption kinetic parameters for pressurized combustion and gasification reactions were determined based on a C++ program coupled with the Langmuir-Hinshelwood (L-H) kinetic model developed and experimental data from pressurized char combustion, and the established L-H kinetic model for pressurized char-O2/H2O combustion was refined in the current paper. The activation energy for desorption in reactions involving pressurized char-O2 and char-H2O was determined to be 250.8 kJ/mol, accompanied by a pre-exponential factor of 5.42 × 1010 g/(m2 s). Using this foundation, the current research conducted simulations to investigate the impacts of temperature, pressure, and H2O concentration on the oxidation adsorption rate (Rads,oxi), desorption rate (Rdes), gasification adsorption rate (Rads,gas), and the competitive influences of kinetics and diffusion processes within the pressurized char-O2/H2O combustion. The simulation results indicate a gradual increase in Rdes and Rads,gas with char conversion to reach a peak, followed by a gradual decline. Conversely, the Rads,oxi varies smoothly throughout the char conversion process. At 1673 K/1.0 MPa, the char-O2/H2O reaction rate is primarily constrained by Rads,oxi and Rads,gas, with the adsorption reaction serving as the rate-controlling step. Moreover, it was noted that a rise in pressure resulted in a linear increase in Rads,oxi, Rdes, and Rads,gas. At elevated temperatures, the impact of pressure on them becomes more noticeable. However, the introduction of H2O mitigates this effect. Elevated temperature and pressure facilitate the competition on the kinetics of char-O2 combustion for O2 diffusion, resulting in the conversion of char being more susceptible to O2 diffusion rate limitation. With the addition of 20 % H2O, the competition effect was weakened. In the case of pressurized combustion involving char and O2/H2O, the char conversion is primarily constrained by the O2 diffusion rate and is scarcely influenced by the H2O diffusion rate.

Numerical study on influences of intake temperature and swirl ratio on in-cylinder combustion and pollutant formation characteristics of ammonia/diesel dual-fuel engine

In order to improve the combustion efficiency of ammonia fuel, and enhance the operational stability and emission level for ammonia engines, this study constructs an in-cylinder combustion numerical model of ammonia/diesel dual-fuel engine based on CONVERGE software, and investigates the effects of initial intake temperature and swirl intensity on in-cylinder combustion and pollutant formation characteristics of ammonia/diesel dual-fuel engine. The results show that increasing the intake temperature can improve the in-cylinder thermal atmosphere, advance the dual-fuel combustion reaction process, and increase the peak in-cylinder combustion pressure and temperature. The peak in-cylinder pressure increases from 6.05 to 6.44 MPa when the intake temperature is increased from 303 to 343 K. This is effective in improving the emissions of incomplete combustion for the ammonia/diesel dual-fuel engine. The in-cylinder unburned NH3, CO and HC emissions are reduced by 20.2 %, 77.1 % and 88.21 %, respectively. Increasing the swirl ratio enhances the in-cylinder gas disturbance, reduces the amount of fuel attached to the wall, and improves the quality of in-cylinder fuel-gas mixture. It also accelerates the process of combustible mixture formation, advances the starting point of ammonia fuel consumption, and accelerates the initial reaction rate. When the swirl ratio is increased from 0.5 to 3.0, the in-cylinder unburned NH3 emission is reduced by 14.85 %. Reasonable adjustment of intake temperature and swirl ratio helps to improve the distribution of direct injection fuel particles inside the cylinder, thereby optimizing the dual-fuel combustion process and enhancing engine performance.

Study on the measurement method and influencing factor analysis for the torsional angle of crankshaft

An improved method is proposed to obtain the torsional angle at both ends of the crankshaft simply and reliably. The installation position deviation is removed with a novel correction method. A digital filter is used to decrease the fluctuation of zero crossing point by 69.8%. The relative variation of torsional angle is increased from 0.818 ℃A and 0.347 ℃A to 1.075 ℃A and 0.474 ℃A respectively for the first and fifth cylinder when the torque is increased, which is attributed to the increasing combustion pressure. With the increasing engine speed, the relative variation of torsional angle increases due to the increasing inertia force. The relative variation of torsional angle is not noticeable under different oil temperature due to the comprehensive influence of combustion and friction torque. The amplitudes of most orders have similar changing trend with the relative variation of torsional angle.