Engine Performance Research Articles

Optimization of Performance, Emissions, and Vibration in a Hydrogen-Diesel Dual-Fuel Engine Using Response Surface Methodology

Background: Dual-fuel diesel engines using hydrogen as a secondary fuel source are a promising technology for reducing emissions while maintaining engine performance. However, optimizing these engines for all three aspects (performance, emissions, and vibration) simultaneously presents a challenge. Objective: This study aimed to address this challenge by employing Response Surface Methodology, a statistical technique used to optimize multi-variable processes. The goal was to find the ideal combination of engine load, hydrogen flow rate, and compression ratio that would maximize Brake Thermal Efficiency while minimizing Brake-Specific Fuel Consumption, Nitrogen Oxide emissions, and engine vibration. Method: A Box-Behnken design, a specific type of design optimization with three factors and three levels, was employed. The experiment evaluated the impact of three key factors: engine load (ranging from 0 - 12 kg), hydrogen flow rate (0-15 L/min), and compression ratio (16 to 18:1). The effects of these factors on performance, emissions, and vibration were measured. Results: The results revealed a trade-off between achieving optimal performance and minimizing emissions. The highest Brake Thermal Efficiency and lowest Brake-Specific Fuel Consumption were achieved at a high compression ratio (18:1), maximum hydrogen flow rate (15 L/min), and under full engine load (12 kg), corresponding to a brake power of 3.5 kW. However, these conditions also resulted in higher NOx emissions and vibration levels. Conversely, minimizing NOx and vibration occurred at a lower compression ratio (16:1), with the same maximum hydrogen flow rate (15 L/min), but at a significantly reduced engine load (3 kg), resulting in a much lower brake power of 0.875 kW. Conclusion: These findings highlight the complex relationship between performance, emissions, and vibration in a hydrogen-diesel dual-fuel engine optimized using Response Surface Methodology. While optimal conditions were identified for specific goals, achieving all desired characteristics simultaneously across the entire operating range remains a challenge.

Performance and emission of a spark-ignition engine using gasoline-plastic pyrolysis oil blends

In response to the problem of plastic waste, this study investigates the conversion of PET waste plastics into Pyrolysis Plastic Oil (PPO) as an environmentally sustainable alternative energy source, aiming to tackle the pressing issue of plastic waste accumulation. Accordingly, the research comprehensively evaluates the physicochemical properties of PPO, examines its impact on engine performance, and determines the optimal concentrations for blending with gasoline. The investigation uncovers the potential of PPO through precise material preparation involving PET plastic waste pyrolysis, employing meticulous testing and analysis for comprehensive insights. Engine testing, conducted on a 125 cc, 4-stroke motorized vehicle, scrutinizes power, torque, and exhaust emissions under various PPO and gasoline blends. The findings reveal distinctive relationships between PPO ratios and engine behavior, emphasizing the need for nuanced fuel blending. The examination extends to fuel consumption and specific fuel consumption (SFC) testing, highlighting PPO's superior SFC. Exhaust emission testing demonstrates reduced emissions with heightened PPO concentration, showcasing its positive environmental impact. The results contribute valuable insights into PPO's viability as an alternative fuel source and its potential role in mitigating plastic waste. A comparative analysis with existing literature enriches our understanding of the field, emphasizing the need for careful consideration in fuel formulation. While PPO may not achieve performance parity with conventional gasoline, its environmental benefits and efficient waste utilization underscore its significance for a sustainable future. Further research is encouraged to optimize PPO properties and blending ratios, paving the way for an eco-friendlier energy landscape.

Applying fischer tropsch and its pentanol blends into an aviation compression ignition engine for PM emissions control

The aviation industry is recovering from COVID-19 to regain rapid growth at an increasing rate of over 5 % annually. Aviation compression ignition (CI) engines attributed to their economic fuel consumption and adorable reliability, have been widely utilized in the general aviation (GA) industry. To fill in the knowledge gap of the compatibility of Fischer Tropsch (FT) blended with long-chain oxygenated fuel applied into the aviation engines, this research focuses on analyzing the combustion performance and particle matter (PM) emissions of an aviation CI engine by burning FT alternative fuel and its pentanol blends (FT80P20 - 80 % FT + 20 % pentanol), in comparison with baseline diesel/pentanol-diesel blends (D80P20 - 80 % diesel + 20 % pentanol). It was found that FT80P20 significantly increases the indicated thermal efficiency (ITE) by 6.5 %, and remarkably decreases the indicated specific fuel consumption (ISFC) by 12 % in contrast to neat diesel at high load (8.5 bar IMEP), which is due to better homogeneous charge that alternates heterogeneous combustion. Moreover, the PM size-resolved number distributions of emissions were characterized. It was observed that the integrated PM emissions from diesel were predominant (∼1.4 × 1014 #/kg∙fuel), while those from FT80P20 were significantly reduced by nearly 85 % (∼0.2 × 1014 #/kg∙fuel). Concurrently, the particulate geometric mean diameter (GMD) were decreased apparently from 80 nm to 35 nm correspondingly. The research findings reveal that “main diffusion combustion” was predominant as burning diesel, while “main premixed combustion” was prominent as using FT80P20, which has a promising impact on effective engine-work promotion with superior PM mitigation.

Experimental analysis and modeling of gas turbine engine performance: Design point and off-design insights through system of equations solutions

In this article, a systematic approach is presented for simulating turbojet engine performance at both design and off-design points. The construction of gas turbine engines involves a core, with additional components added based on the proposed methodology. Accurate formulation of component characteristics and their matching forms the basis for the system of equations needed for solving off-design engine performance. The developed algorithm's initial step involves comparing results with experimental data obtained from 230 N engines. Experimental testing utilizes a 780 N engine under diverse operating conditions, allowing determination of thrust values, fuel consumption, and outlet gas temperatures. An engine characteristic curve is derived under static conditions at ground level and validated against ground test results in Tehran. Unknown parameters are calibrated using a dedicated model, enabling the extraction of engine performance parameters across different corrected speeds. These results are then compared with GasTurb outputs. Comparative analysis between the proposed model's simulation and experimental data demonstrates high accuracy, affirming the reliability of the presented model.

Investigation of biodiesel and its blends fueled diesel engine: An evaluation of the comprehensive performance of diesel engines

The carbon-neutral era and the increasing demand for energy worldwide are imperative for researching alternative energy. At the same time, biodiesel is considered one of the most prospective alternative energy due to its renewable nature and similar properties to diesel. A comparative study of the effects of different proportions of biodiesel-diesel blends (BD10, BD20, BD40, BD60, BD100) on emissions, vibration, lubricant ferrography, and tribological performance of cylinder liner-piston ring (CL-PR) of a direct injection diesel engine (ZS195) was carried out with a baseline of petroleum diesel. The results of the study demonstrated that the appropriate proportion (less than 20 %) of biodiesel significantly improves the comprehensive performance of diesel engines, primarily by combustion optimization and vibration shock reduction. The BD20 fuel blend achieves the best comprehensive diesel engine performance. The higher percentage of biodiesel results in enhanced vibration and severe degradation of CL-PR performance caused by the dilution of the lubricant and erosion of the components by the biodiesel. The study illuminates the mechanism and intrinsic connection of the effects of biodiesel on diesel engine performance. These results will facilitate the understanding of the effects of biodiesel-diesel blends on diesel engine performance and contribute to carbon neutrality in the transportation sector.

Flow field design and simulation in electrochemical machining for closed integral components

Using closed integral components (CICs) not only simplifies the structure and reduces the weight of aeroengine components but also reduces the number of parts and improves overall engine performance. However, there are currently few publicly available reports on the electrochemical machining (ECM) of CIC blades. The key factor influencing the stability of ECM is the flow-field, which is difficult to design for a CIC because its two sides are closed, thereby limiting the direction of electrolyte flow into the processing area. To achieve the ECM of CICs, flow modes involving either lateral or composite liquid supply (LLS or CLS) are proposed, followed by flow-field and cathode-deformation simulation analyses. The simulation results show that the CLS flow-field is more reasonably designed and its electrolyte distribution is more uniform. The maximum cathode deformation under CLS flow-field is only ca. 15 µm. The experiments were conducted to improve the efficiency of CIC ECM and compare the LLS and CLS flow-fields. During processing, the feed rate was increased from 0.2 min/mm to 0.45 min/mm, and the surface roughness (Ra) decreased from ca. 1.29 µm to ca. 0.37 µm. The experiments show that the CLS flow-field offers higher processing efficiency and better surface quality.

Evaluation of emission of the hydrogen-enriched diesel engine through machine learning

Improving the engine operation by implementing intelligent algorithms is crucial for meeting stricter emissions regulations and enhancing engine performance. Therefore, in this study, hydrogen enrichment effects on emissions from a diesel engine were examined. The diesel engine's intake port was used to add hydrogen. Different quantities of hydrogen (2.5–13 lpm) were used to study the effects of hydrogen on the diesel engine at various engine loads (0–100 %) and speeds. The results of the study indicate that machine learning methods are highly effective modeling techniques with a high level of accuracy. Moreover, XGBoost outperformed other methods regarding its prediction performance, specifically for CO2 (R2 = 0.997) compared to random forest prediction (R2 = 0.964). These techniques strongly agreed with experimental findings, ranging from 97 % to 99 %. Other machine learning algorithms were also used to predict CO and NOx, but their R2 values were slightly lower than those of machine learning models, further highlighting the excellent predictive capabilities of XGBoost modeling.

Control strategies for mode switching of a large marine two-stroke engine equipped with exhaust gas recirculation and turbocharger cut-off systems

To meet the stringent nitrogen oxides emissions regulations, the recent marine two-stroke engines are equipped with exhaust gas recirculation (EGR) systems. Crossing the boundaries of exhaust control areas requires switching between the engine operating modes associated with the activation or deactivation the EGR system, which imposes challenges to the engine operation. This study aims to develop and numerically test effective control strategies for improving the mode switching of marine two-stroke engines with EGR systems. The investigated engine dynamic model is developed by integrating a zero-dimensional thermodynamic model developed in GT-POWER and the control model developed in MATLAB/Simulink. This model is first validated against the experimentally measured engine performance parameters, and subsequently employed to simulate the engine dynamic operation with mode switching. The simulation results are assessed to quantify the impact of several control strategies on the engine performance. The derived perrformannce parameters time variations demonstrate that the deactivation of the EGR branch and the small engine–turbocharger result in exceeding the manufacturer limits at high loads and increasing the fuel consumption. The proposed load-based control strategies, which employ load thresholds and time delays for the control of the EGR and turbocharging systems activation/deactivation, are proved effective, as the engine performance parameters are retained within their limits and fuel consumption penalties are minimised. This study provides insights for developing the control of the marine engines after-treatment systems, hence contributing towards enhancing shipping sustainability.

The investigation of the performance and exhaust emissions of the compression-ignition engine with a mixture of diesel and aluminum particles

In this study, aluminum particles were added to diesel fuel in amounts of 75 and 150 ppm, with a particle size of 15 micrometers and a purity of 98.95 %. A magnetic stirrer was used to achieve homogeneous mixing of aluminum particles in diesel. In order to prevent aluminum particles from settling, fuel mixtures were stirred for 45 minutes for every 2 kg of fuel mixture. Fuel mixtures prepared to prevent settling were used immediately to avoid affecting the experimental results. The experiments were conducted at torque values of 100, 150, and 200 Nm, with a constant 660 rpm. The experiments initially started with pure diesel. Then, they continued with diesel fuels containing 75 and 150 ppm of aluminum additives, respectively. Positive effects of aluminum addition on engine performance were observed. The highest efficiency was obtained with the fuel containing 75 ppm of aluminum additive. The fuel with 75 ppm of aluminum additive provided efficiency increases of 4.57 %, 2.90 %, and 2.23 % compared to pure diesel at torque values of 100, 150, and 200 Nm, respectively. Although the fuel with 150 ppm of aluminum additive showed less efficiency improvement compared to 75 ppm, it still provided efficiency improvement compared to pure diesel. Improvements in NOx, CO, and HC emissions were observed in experiments conducted with aluminum particle-added fuels. The aim of this study is to increase the efficiency of diesel engines and reduce exhaust emissions by using aluminum particle additives.

Effect of addition of biodiesel having Karanja oil on exhaust emissions and performance in a diesel engine with hydrogen as a secondary fuel

With a specific end goal to take care of the worldwide demand for energy, broad research is done to create alternative and cost-effective fuel. The fundamental goal of this examination is to investigate the performance, emissions and vibration characteristics of a single cylinder four stroke diesel engine, working in dual fuel mode with biodiesel of Karanja oil ((BKO) as a renewable fuel and hydrogen (H2) as gaseous fuel on low (2%), intermediate between medium-high (53%) and high (69%) load conditions. Biodiesel of Karanja oil as 20% biodiesel and 80% diesel known as BKO20, while 30% biodiesel and 70% diesel known as BKO30. With 25% introduction of gaseous fuel (H2) and biodiesel (10%–40%) along with diesel showed an increase in brake thermal efficiency (BTE), 85.23%, 10.62% and 19.4% respectively as compared to parent diesel fuel operation. As far as emission is concerned, oxides of nitrogen (NOx) decreased on higher load conditions with a variation of biodiesel (10%–50%) in comparison to low load condition. However, the formation of monoxide (CO), carbon dioxide (CO2) and un-burnt hydrocarbon (HC) decreases along with BKO50 using 25% hydrogen fuel substitution at high (69%) load conditions.

Convection Heat-Transfer Characteristics of Supercritical Pressure RP-3 in Horizontal Microchannels

To enhance the heat-transfer performance of scramjet engines, a numerical simulation was conducted on the heat-transfer process of RP-3 aviation kerosene under supercritical pressure within a horizontal micro-fine circular tube. The intrinsic mechanism of the heat-transfer process was analyzed, summarizing the impacts of mass flux, inlet temperature, and gravitational acceleration. Furthermore, four commonly used buoyancy criterion numbers were compared and evaluated. The results indicate that the heat-transfer process can be divided into five phases: heating inlet phase, normal heat-transfer phase, heat-transfer deterioration phase, heat-transfer enhancement phase, and high-temperature normal heat-transfer phase. The heating inlet phase is significantly influenced by the inlet temperature, while the heat-transfer deterioration is affected both by the thermal property variations of the aviation kerosene and the buoyancy effects. Lower mass flux and hypergravity conditions all exacerbate heat-transfer deterioration. Inlet temperature, however, does not affect the heat-transfer pattern. Among the criteria, Grq/Grth provides the best prediction of buoyancy effects in horizontal circular tubes.

Advancements in biofuel research: Understanding the physical and chemical characteristics of green diesel

Green diesel is a potential biofuel that offers certain advantages over traditional fossil diesel, such as low environmental pollution and no sulfur. However, there is little information available regarding the density and viscosity of green diesel, which is crucial for the quality control of biofuels and their performance in engines. In this study, the properties of green diesel produced from palm and soybean oils hydrotreatment were investigated, and models were developed to predict the physical properties of green diesel and n-alkanes. The experimental measurements had uncertainties of 1×10-4 g/cm3 and 1×10-2 mPa s in density and viscosity, respectively. The models were found to be in good agreement with the experimental values. The study highlights the importance of density and viscosity for quality control and engine performance of biofuels. The developed models for predicting the physical properties of green diesel and n-alkanes can be useful for quality control and optimization of biofuel production processes. The findings can be useful for researchers, engineers, and policymakers working in the field of biofuels and renewable energy. Further research is needed to explore the applicability of the developed models to other types of biofuels and to investigate the environmental and economic sustainability of green diesel production.

Implementation of Failure Mode and Effect Analysis (FMEA) for centrifugal pump maintenance in water supply distribution system

A centrifugal pump is an essential mechanical device in the Regional Drinking Water Company (PDAM) to distribute sterile water from the reservoir to local community houses by flowing the fluid through the pipeline. However, improper and inadequate maintenance of centrifugal pumps can result in component damage, including bearings that are broken, ripped, or damaged mechanical seals. Therefore, for the water supply to continue smoothly, proper maintenance needs to be carried out so that the engine's performance will be maintained and last longer. This study aims to conduct a maintenance analysis on centrifugal pumps utilized by the PDAM of Madiun City. The Failure Modes and Effects Analysis (FMEA) method was employed to assess the potential failure of a system, design, process, or service by implementing a systematic approach to analyze damage and devise maintenance strategies. The FMEA analysis revealed that the shaft of the centrifugal pump component had the highest Risk Priority Number (RPN) value, which amounts to 294. The wearing ring had the lowest RPN value among the centrifugal pump components, with a value of 54. The Pareto diagram results classified six components: shaft, clutch, stuffing box, motor, impeller, and mechanical seal to recommend preventative maintenance action. Additionally, three other components suggested for corrective maintenance were the bearing, packing, and wearing rings

Novel biofuel blends for diesel engines: Optimizing engine performance and emissions with C. cohnii microalgae biodiesel and algae-derived renewable diesel blends

Fossil diesel is a significant global fuel; however, environmental concerns and resource scarcity necessitate alternative fuels. Third-generation microalgae biodiesel (MB), despite its carbon neutrality, leads to higher oxides of nitrogen (NOx) emissions and poor engine performance. Renewable diesel (RD), also known as hydrotreated vegetable oil (HVO), could reduce these issues. A quasi-dimensional multi-zone combustion model is employed in this study to look into how different fuel blends of diesel, C. cohnii MB, and algae-derived RD affect the performance, combustion, and emissions of a compression ignition (CI) engine. The study uses a 2000 rpm engine arrangement with different engine loads, and validates the computational analysis with an experimental test engine arrangement. The study aims to explore the potential of sustainable biofuels in CI engines. D70MB30 (70 vol% diesel, and 30 vol% MB) fuel blend leads to a higher ignition delay period (IDP) while lowering peak cylinder pressure (PCP) and peak heat release rate (PHRR) compared to D100; however, when RD is added to diesel-MB fuel blends, it reduces IDP and increases PCP and PHRR. Brake specific fuel consumption (BSFC) for the D70MB30 blend rises by 5.28–8.9 %, while brake thermal efficiency (BTE) reduces by 0.98–4.27 %. However, RD in MB blends reduces BSFC by 1.57–3.41 % and marginally enhances BTE, resulting in greater fuel economy and efficiency. D70MB30 fuel blend results in higher specific carbon dioxide (CO2) emissions and oxides of nitrogen (NOx) emissions while lowering particulate matter (PM) and smoke emissions compared to neat diesel due to its high intrinsic oxygen content. In contrast, RD with the MB blend reduces specific CO2 and NOx emissions; however, it increases PM and smoke emissions due to the NOx-PM trade-off. The optimum results occur with a full load and D70MB15RD15 (70 vol% diesel, 15 vol% MB, and 15 vol% RD) fuel blend. Compared to the D70MB30 blend, D70MB15RD15 reduces BSFC, specific CO2, and NOx by 2.15 %, ∼1%, and 8.37 %, respectively, while increasing PM emissions at 100 % load.

Impact of hydrogen-assisted combustion in a toroidal re-entrant combustion chamber powered by rapeseed oil/waste cooking oil biodiesel

This study investigates the performance and emission characteristics of biodiesel blends of rapeseed oil and waste cooking oil in a toroidal re-entrant combustion chamber (TCC) compression ignition engine. Hydrogen was allowed into the engine in dual fuel mode to enhance the engine performance. The presence of oxygen in the biodiesel and hydrogen induction increased the peak pressure and heat release rate significantly for all the engine loads. At a peak load of 4.88 kW, the maximum brake thermal efficiency (BTE) of 31.77% was recorded for the D70R20W10 (diesel 70%, rapeseed oil 20%, waste cooking oil 10%) biodiesel blend. Furthermore, hydrogen induction enhanced the BTE by around 3%. The biodiesel blending substantially lowered the emissions of unburnt hydrocarbons, carbon monoxide, and smoke opacity. Additionally, hydrogen supplementation facilitated 5–10% carbon monoxide reduction over biodiesel blends by enabling more complete oxidation. However, higher temperatures generated due to complete combustion resulted in more NOx formation. Thus, the authors propose that biodiesel blends of rapeseed oil, waste cooking oil, and diesel with hydrogen induction improve engine performance and reduce regulated emissions.

Experimental investigation on the impact of fuel injection schemes on the fuel/air mixing characteristics in alternating wedge struts

To enhance the performance of scramjet engines, it is essential to understand the fuel/air mixing characteristics downstream of alternating wedge struts and the dynamics of streamwise vortices. Two optical measurement techniques, Mie scattering and acetone-particle laser-induced fluorescence, were employed to study the impact of fuel injection location and different injection gases on the fuel/air mixing characteristics downstream of alternating wedge struts at total temperature of 300 K and total pressure of 800 kPa. The results indicated that the particle laser-induced fluorescence measurements provided superior results compared to Mie scattering, due to the more uniform distribution and better following characteristics of acetone molecules as seeding particles. Different fuel injection locations resulted in varying fuel distributions and plume morphologies downstream. The plume sizes obtained from the three types of fuel orifices were generally consistent, but the mixing effect of the orifices on the first strut was better, whose injection locations being at the trailing edge intersections, with a larger plume area and more uniform fuel distribution. The fuel/air mixing process downstream of the alternating wedge struts was primarily dominated by streamwise vortices. Despite certain differences in the physical properties of nitrogen and hydrogen molecules, the measurement results showed that the plume morphologies obtained with both gases were quite similar. Additionally, a streamwise vortex model was developed to predict the dynamics of streamwise vortices and the evolution of fuel plume morphology, and it was compared with experimental results.

Performance and Emission Characterization of a High-Injection Pressure Common Rail Diesel Engine Fueled by Blended Diesel and TiO2 Nanoparticles.

Abstract How to increase engine power and reduce fuel consumption and emission is an important target that engine designers try to achieve it. One of the most promising approaches to realise this goal is adding nano additives to fuel. Titanium dioxide (TiO2) blended with biofuels get wide studies by researchers using conventional diesel engines at different operating regimes. This work aims to prolong these investigations using diesel fuel, rather than biofuels, on a high injection pressure (1400 – 1600 bar) common rail diesel engine at wide operating conditions and different TiO2 concentrations. Experimental outcomes show an increase in peak cylinder pressure up to 8.51% than pure diesel when using 100 ppm TiO2 concentration. Also, BSFC has been decreased by 36%, and BTE increased by 48% compared to pure diesel at high speeds and loads. NOx and CO2 emissions raised by 35.3% and 40.3% respectively, while CO emissions decreased by 35%. These results could be a reason for further studies for TiO2 using different sizes, at wider engine regimes and mixture strengths.

Numerical and Experimental Analyses of the Effect of Water Injection on Combustion of Mg-Based Hydroreactive Fuels

The energy release process of the Mg-based hydroreactive fuels directly affects the performance of water ramjet engines, and the burning rate is one of the key parameters of the Mg-based hydroreactive fuels. However, there is not enough in-depth understanding of the combustion process of Mg-based hydroreactive fuels within the chamber of water ramjet engines, and there is a lack of effective means of prediction of the burning rate. Therefore, this paper aims to examine the flame structure of Mg-based hydroreactive fuels with a high metal content and analyze the impact of the water injection velocity and droplet diameter on the combustion property. A combustion experiment system was designed to replicate the combustion of Mg-based hydroreactive fuels within water ramjet engines, and the average linear burning rate was calculated through the target line method. On the basis of the experiment, a combustion–flow coupling solution model of Mg-based hydroreactive fuels was formulated, including the reaction mechanism between Mg/H2O and the decomposition products from an oxidizer and binder. The model was validated through experimental results with Mg-based hydroreactive fuels at various pressures and water injection velocities. The mean absolute percentage error (MAPE) in the experimental results was less than 5%, proving the accuracy and validity of the model. The resulting model was employed for simulating the combustion of Mg-based hydroreactive fuels under different water injection parameters. The addition of water injection resulted in the creation of a new high-temperature region, namely the Mg/H2O non-premixed combustion region in addition to improving the radial diffusion of the flame. With the increasing water injection velocity, the characteristic distance of Mg/H2O non-premixed combustion region is decreased, which enhances the heat transfer to burning surface and accelerates the fuel combustion. The impact of droplet parameters was investigated, revealing that larger droplets enhance the penetration of the fuel-rich gas, which is similar to the effect of injection velocity. However, when the droplet size becomes too large, the aqueous droplets do not fully evaporate, resulting in a slight decrease in the burning rate. These findings enhance the understanding of the mechanisms behind the burning rate variation in Mg-based hydroreactive fuels and offer theoretical guidance for the optimal selection of the engine operating parameters.

Effect of thermodynamic-dynamic parameters on the oscillation and performance of a free piston Stirling engine

This paper presents an analysis of the oscillation and parametric performance of a gamma-type free piston Stirling engine using a thermodynamic-dynamic nonlinear model. Firstly, the concept of oscillation and impact cylinder points is defined and a method for determining the stable oscillation zone of the free piston Stirling engine is proposed. Besides, the effects of various thermodynamic parameters on the system’s performance, such as charging pressure, hot-end and cold-end temperatures, and dynamic parameters (such as the masses and spring stiffness of the displacer and piston), are investigated. The oscillation zone takes on a “V” shape when the piston and displacer masses or stiffness, and hot-end temperature and displacer stiffness, are varied. Finally, the output power and operating frequency of the impact cylinder line are determined. The results show that maximum output power and operating frequency of 75.36 W at 58.21 Hz or 76.73 W at 58.61 Hz are achieved at the “V” bottom when either the piston and displacer masses are adjusted or their stiffness properties are varied. Additionally, consistent output power and operating frequency of 125.35 W and 75.08 Hz, and 104.63 W and 68.59 Hz, are obtained regardless of changes in both displacer mass and stiffness.

Improve the thermal performance of precooler by enhancing the utilization of chemical heat sink: Refined design method and characteristic analysis

The chemical heat sink of the coolant plays a crucial role in enhancing the performance of the precooler, which affects the overall performance of the air-breathing precooled engines. The conventional thermal design method for precoolers cannot accurately evaluate the chemical heat sink of coolants. To address this crucial issue, this paper proposes a refined model that considers the chemical reaction processes of n-Decane, based on a two-dimensional discretization unit model and the plug flow reactor model incorporating molecular-level chemical reaction mechanisms. The validation of this model is conducted by comparing it with publicly accessible data and computational fluid dynamics simulations, thereby demonstrating its excellent accuracy. Subsequently, an analysis is conducted on the factors influencing the chemical heat sink release of the coolant within the precooler, and enhanced design criteria for optimizing chemical heat sink utilization are proposed. Building upon these considerations, the performance of a precooler with a design point of Mach number 5 under off-design conditions was analyzed. The findings indicate that employing rational design methods can enhance the chemical heat sink efficiency of endothermic fuels by 8.0%, along with a concurrent 10.3% increase in the total heat sink. This underscores the significance of considering the impact of the chemical heat sink of endothermic fuels in the design of precoolers. In the case presented in this paper, the contribution of the chemical heat sink to the total heat sink within the n-Decane precooler could reach 35.3%.