Cylinder Pressure Research Articles

Freight train air brake modelling with emergency valves

The 120-type air brake system is unique around global rail industry and critical for Chinese freight train operation. Existing research about its simulations does not include detailed models for the emergency brake valves. This paper filled this research gap by developing a detailed fluid dynamic air brake system with a focus on the emergency brake valve. The working principle of the emergency brake vale was reviewed. The brake system model was based on gas flow governing equations (mass and momentum) and orifice flow equations. The model was validated by comparing with measured data from a 150-wagon train. Four braking scenarios were compared. The simulated maximum cylinder pressure was only 5 kPa out of the range of the measured data. The maximum difference regarding the time when cylinder pressure reaches maximum pressure was 4 s. The simulation results have also shown variable switch pressure points for the two-stage brake valve. This is agreed by the measured results and was not shown in previously published research.

Study on the aerodynamic characteristics and flow mechanism of square cylinders with rounded corners

In order to elucidate the variation patterns of the aerodynamic characteristics of square cylinders with rounded corners with respect to corner radius ratio and angles of incidence, and to reveal their underlying mechanisms, a wind tunnel test was performed to examine the surface wind pressure of square cylinders with a corner radius ratio R/D (where R represents the corner radius and D signifies the characteristic dimension of the object) of 0, 0.1, 0.2, 0.3, and 0.4. The experiment was conducted at a Reynolds number of 120,000 while varying the angles of incidence between 0° and 45°. In this study, aerodynamic forces, Strouhal numbers, and wind pressure were analyzed. Additionally, the flow field was visualized using a large eddy simulation (LES). The results indicate that the critical angle of incidence αcr of square cylinders with rounded corners decreases as the corner radius ratio increases. αcr represents the angle at which the mean drag and fluctuating lift are minimum and the mean lift and Strouhal number are maximum. Significant negative pressure is observed near the windward rounded corner of the square cylinders with rounded corners in the vicinity of αcr, with the highest value occurring at an R/D of 0.2. Fluctuating wind pressures could attain larger values in the vicinity of the leeward rounded corners where α = 12.5°∼20° and α = 45°. Increasing R/D to a certain value significantly alters the flow structure compared to a square cylinder with R/D= 0. This is due to the shear layer flowing close to the wall, as it does not separate at the windward rounded corner.

Effect of multi-injection strategy on characteristics of methanol-fueled direct injection spark ignition engine

Present paper numerically investigates the effect of injection strategy and start of injection (SOI) timing on in-cylinder flow, air–fuel mixing, fuel distribution near spark plug, engine performance, and exhaust emissions for highly stratified methanol-fueled, multi-injection, direct injection spark ignition engine having high compression ratio. SOI is kept constant at −23° crank angle (CA) after top dead center (ATDC) with a spark timing (ST) of −2° crank angle (CA) ATDC. Mass of fuel is divided into pilot and main injection ports having pilot to main fuel injection mass ratio of 1:1, 1:2, and 1:3 at 0° and 2° dwell times between main and pilot injections. As the quantity of fuel in main injection increases, pressure rise rate increases, which results in higher in-cylinder pressure and higher rate of burning that gives higher apparent heat release. Due to higher peak pressure rise rate and faster burning in the case of 2° crank angle (CA) dwell time, shorter combustion duration is achieved compared to 0° crank angle (CA) dwell time. In the case of multi-injection, faster burning rate enhanced in-cylinder temperature; therefore, nitrogen oxides (NOx) emissions are higher. Pilot to main fuel mass ratio of 1:3 has resulted highest indicated thermal efficiency, lowest specific fuel consumption, lowest soot, and carbon monoxide (CO) emissions.

A Constant Pressure Cylinder Coupled With a “Zero-Stiffness” Eddy Current Damper

A Constant Pressure Cylinder Coupled With a “Zero-Stiffness” Eddy Current Damper

Maximizing waste plastic oil yield and enhancing energy and environmental metrics through pyrolysis process optimization and fuel modification

The accumulation of plastic waste poses a major environmental challenge, while the conversion of waste plastics into oil via pyrolysis holds promise as an alternative energy solution. Despite numerous investigations into this area, none have focused on optimizing pyrolysis process parameters for higher oil yield and enhancing the overall performance of plastic oil through suitable fuel modification. The present study aims to optimize the pyrolysis process parameters, including heating rate (HR), process temperature (PT), and reaction time (RT), to achieve a higher yield of waste plastic oil (WPO) and enhance the overall performance by blending optimal quantities of water. Fuel characterization and properties measurement were conducted using Fourier Transform Infrared and ASTM methods. WPO was blended with conventional diesel fuel (CDF) and different volume concentrations of water (5%, 10%, and 15%). The performance metrices were assessed under various engine conditions. The study findings indicate that the optimum condition of process parameters is an HR of 17.3 °C/min, PT of 403 °C, and RT of 96.30 min, and the fuel quality confirms its suitability as an alternative fuel source. The performance metrics revealed that WPO has a 5.4% lower brake-thermal efficiency than CDF, and the inclusion of 10% water in WPO (WPO10W) enhances the efficiency by 11.5%. The in-cylinder pressure and net-heat release rate of WPO are 1.3% and 12.9% lower than CDF, respectively, and WPO10W emulsion promotes efficient combustion. WPO10W emulsion fuel reduces oxides of nitrogen, hydrocarbon, and carbon monoxide emissions by 21.2%, 9.8%, and 22.2%, respectively, compared to WPO.

Rational Mode Parameters of Power Units Operating in Modern Energy Market Conditions

The paper analyzes the operation of condensing and heating turbines in modern energy market conditions with an assessment of the impact of operating parameters of live and secondary steam on economic indicators. It has been shown that when operating at variable loads, the most effective in terms of high-pressure turbines is a rational reduction in the initial pressure ps (sliding pressure), which leads to an increase in thermal efficiency by 1-1.5%. The experimental results of a study of the vacuum effect in the condenser on fuel consumption are presented in the paper as well. Using a specific example of the K-320-26.5 turbine unit, the need for a rational choice of cooling water flow in winter season to ensure optimal vacuum is shown. The issue of choosing a rational steam reheat temperature tr is examined in more detail. It has been established that one of the main reasons for the decrease in the efficiency of turbine units when operating in variable modes is the irrational use of the reheat temperature and the heat of phase transition in the flow part of the low pressure cylinder. The physical explanation of these processes in the turbine as tr decreases is given in detail. It has been shown that, as a result of analyzing the operation of turbine units of various capacities, a rational choice of reheat temperature (reducing tr by 10-20 °C) increases thermal efficiency by 1-2 %, and turbine efficiency - by 0.4-1.0 %. It is recommended to consider the pressure of the hot steam of the high pressure cylinder (рs), the pressure in the condenser (рc=f(tcirc.water)), as well as the reheating temperature tr, which altogether leads to a reduction in heat consumption by 2.5-3.5 % as rational parameters of steam when operating in variable modes. In order to increase the economic efficiency of the operation of turbine units of TPPs and CPPs at reduced loads, it is recommended to revise the regulatory documentation on the current amendments for changes in the reheat temperature. It is stated that with strict adherence to the recommendations discussed above, fuel savings at TTPs and CHPs in Ukraine can amount to 250–300 thousand tons of coal per year.

The Combustion and Emission Characteristics of Corn Oil Biodiesel with Titanium Oxide (TiO2) Nano-additive

This experiment produced biodiesel from corn oil through transesterification. Fuel mixture proportions were changed to assess engine performance and reduce fossil fuel emissions. This study examined brake power, mean effective pressure, mechanical efficiency, brake thermal efficiency and indicated thermal efficiency, and emissions such as hydrocarbons, carbon monoxide and NOx. 20% of corn oil was blended with diesel to make biodiesel. The fuel characteristics of the corn oil methyl ester matched ASTM standards. Experimental results were obtained by operating a single-cylinder four-stroke diesel engine under various load conditions. Titanium oxide nanoparticles in the biodiesel reduced HC and CO engine emissions whereas, there was an increase in CO2 and NOx emissions. Combustion parameters such as cumulative net heat release rate and fuel line pressure decreased whereas, cylinder pressure and net heat release rate increased; the sample BD20 + 100 ppm TiO2 sample exhibited appreciable results.

Numerical Analysis of the Effects of Fuel Injection Duration and Spray Angle on the Combustion Process in a Compression Ignition Engine

The changes in injection strategies for diesel engines have a major impact on the performance and pollutant emission characteristics of diesel engines. If injection strategies like injection duration, injection timing, injection pressure and spray angle are properly adjusted, combustion can be improved. The engine performance will increase and emissions will decrease with the combustion improvement. In this work, the influences of injection duration and spray angle on the combustion characteristics of single cylinder, natural aspirated, electronically controlled injection, compression ignition engine were investigated. In the first stage of the work, experiments were executed on a single cylinder CI engine using a Cussons P8160 DC dynamometer. After the experiments, the piston bowl geometry of the engine was modeled and numerical simulation studies were achieved at 7 different injection durations and 7 different spray angles using Converge CFD software. As a result of this study, it was observed that there is a good match between experimental and simulation data of heat release rate (HRR) and in-cylinder pressure. In-cylinder pressure decreased with longer injection duration. The highest max. in-cylinder pressure was roughly 101.0 bar at 4°CA injection duration and the lowest max. in-cylinder pressure was roughly 82.0 bar at 10°CA injection duration. When the HRR data were analyzed, it was seen that as the injection duration increased, the amount of heat released by combustion decreased. When examining the results of the spray angle analysis, it was concluded that there were not very large differences in-cylinder pressure and HRR data, and there was a difference of 1.4 bar between the highest and lowest max. in-cylinder pressure values. In addition, the highest in-cylinder pressure of approximately 86.7 bar was obtained at a spray angle of 77°. It was observed that the CA50 value was obtained at angles closer to the top dead center by increasing the spray angle and decreasing the injection duration. Moreover, the longest combustion durations were realized at 60° spray angle and 10°CA injection duration.

Investigation of the effects of single and double-walled carbon nanotube utilization on diesel engine combustion, emissions, and performance

In this study, single-walled carbon nanotubes (SWCNT) and double-walled carbon nanotubes (DWCNT) were separately added to diesel fuel to investigate their effects on the combustion, performance, and emission characteristics of a diesel engine. SWCNT and DWCNT were added to diesel fuel at concentrations of 100 mg/L with the assistance of ultrasonication, resulting in the creation of DFCNT-1 and DFCNT-2 fuels. Fuel samples were tested at 1500 rpm under varying load conditions. The results indicated significant increases in combustion parameters such as cylinder pressure (CP), Net Heat Release Rate (NHRR), Rate of Pressure Rise (ROPR), Cumulative Heat Release (CHR), and average gas temperature (MGT) for DFCNT-1 and DFCNT-2 fuels. Additionally, the use of DFCNT-1 and DFCNT-2 fuels led to a decrease in carbon monoxide and smoke emissions while nitrogen oxide and carbon dioxide emissions increased. The Brake Specific Fuel Consumption (BSFC) decreased by 7.59% and 4.29% with the use of DFCNT-1 and DFCNT-2, respectively. Moreover, a shorter ignition delay (ID) and combustion duration (CD) were observed with DFCNT-1 and DFCNT-2 fuels. Overall, it was concluded that the addition of SWCNT was more effective than DWCNT in terms of combustion efficiency, performance, and emissions.

Optimization of biodiesel production parameters for hybrid oil using RSM and ANN technique and its effect on engine performance, combustion, and emission characteristics

The increased need for renewable energy sources and growing concerns about environmental pollution has driven the need for alternative fuels (particularly biodiesel) in the transportation industry. The most used technique for producing biodiesel is transesterification, which involves the oil reacting with alcohol in the presence of a catalyst. This study looks at the usage of artificial neural network (ANN) and response surface methodology (RSM) to optimize biodiesel synthesis factors for a hybrid oil feedstock (30% cottonseed and 70% spirulina microalgae oil). The parameters that were optimized were the methanol/oil ratio, reaction time, and catalyst concentration. Cottonseed oil was combined with spirulina microalgae oil to minimize its higher free fatty acid content to less than 1% and prevent soap formation during the transesterification process. The optimal biodiesel production was 94.37%, with 106.4 minutes of reaction time, 1.612% catalyst loading, and a methanol/oil ratio of 20:1. The optimized findings, when confirmed with experiments, gave a biodiesel yield of 91.03% with an error of 3.6%. To provide vital insights into the potential environmental benefits of using this alternative fuel, the study further investigates how the optimized biodiesel blend influences engine performance and emission characteristics. Testing was done at 1500 RPM and 17.5 CR for maximum loading conditions, diesel, HBD20, and HBD fuel produced 0.2746, 0.2805, and 0.288 kg/kWh of specific fuel consumption (SFC), respectively. The CO2 emissions of HBD and HBD20 were 2.49% and 8.30% lower, respectively, than pure diesel. NOx emissions increased by 14% and 18.3%. The highest cylinder pressure was 66.87 at 363 °C.

Experimental investigation on diesel engine operating with CuO nanoparticles dispersed Azadirachta indica biodiesel

This study aims to ascertain the operating parameters of a Copper oxide nanoparticle and Azadirachta indica biodiesel-powered diesel engine. Copper oxide nanoparticles were considered at 75 ppm, and three dispersants were added at the same ratio as nanoparticles. An ultrasonic bath sonicator was used to sonicate the nanoparticles, and later, the ultrasonicator was used to prepare the nanofuel. The experiment was conducted on a diesel engine with different injection timings, such as 21 °bTDC, 23 °bTDC, and 25 °bTDC at full load. The performance was slightly improved by mixing nanoparticles with B20, and it got even better by adding dispersants. The combustion parameters were also changed compared to diesel. Finally, the emissions of carbon monoxide, unburnt hydrocarbons, nitrogen oxides and smoke opacity were significantly reduced by the dispersion of nanoparticles. Increasing the injection timing also led to better results, and 25 °bTDC showed better results. The B20+CuO75+QPAN 75 has shown the most remarkable effects among other samples. At 25°bTDC, the brake thermal efficiency, brake specific fuel consumption, cylinder pressure, net heat release rate, were 35.03 %, 0.391 kg/kWh, 66.23 bar, and 89.39 J/°CA, respectively, while carbon monoxide, unburnt hydro carbons, smoke, and oxides of nitrogen were 0.089 %, 32 ppm, 19.351 %, and 1238 ppm.

Combustion characteristics and performance analysis of a heavy-fuel rotary engine by designing fuel injection position

The heavy fuel rotary engine commonly operates under high-pressure direct injection, lean-burn and spark-assisted ignition modes, this characteristic feature further highlights the significance of the distance between fuel injection position (FIP) and assisted spark plug in engine combustion organization and performance improvement. Thus, a computational fluid dynamics (CFD) means coupled with chemical reaction kinetics is used to investigate the FIP effects on the fuel stratification rule and combustion performance of a heavy-fuel rotary engine. Meanwhile, the flow and combustion transient information in the narrow combustion chamber is analyzed by considering five specially designed FIPs, whose distances to the assisted spark plug along the X-axis (major axis) are 25, 30, 35, 40 and 45 (mm). The results indicate that the distance increases to 40 mm (FIP-40) and 45 mm (FIP-45), the fuel stratified distribution rule is more rational, the mixture burn rate accelerates, combustion time reduces, and combustion performance improves significantly. The FIP-45 scheme is the preferred engineering application scheme after comprehensively assessing engine performance parameters, and when compared to the FIP-35 (original scheme) its peak cylinder pressure (Pmax) increases by 5.3 %, CA10-90 accelerates by 20.4 %, and main emissions of Soot, NO and CO reduce by 48.1 %, 50.0 % and 36.2 % respectively, while CO2 increase.

Combustion performance and emission characteristics of aloevera diesel-emulsified fuel in a DI diesel engine.

Nowadays, mankind is very particular about the usage of energy in the most effective manner by keeping the view of less adulterating the atmosphere, which are the key aspects of many scientists all around the world. In this particular study, the aloevera diesel has been chosen as the primary fuel, and studies have been conducted on emission pollutant characteristics by choosing an appropriate diesel engine. Furthermore, stable emulsions have been produced by using aloevera, and the same was mixed with diesel at the ratio of 5% and 10% as the compound. Moreover, span 80 and tween 80 are used as the surfactant with an HLB balance of 9.95. Similarly, the emulsions are prepared with the help of a mechanical stirrer for exact duration of 30min. In order to carry out the experimental investigation process, a single-cylinder diesel engine was used with a data acquisition system. The entire analyses are carried out with two sets of methods such as no load and full load. The performance and combustion characteristics such as heat release, combustion pressure, thermal efficiency (B5 - 6.303%↑, B10 - 3.789%↑), and specific fuel consumption of the brake (B5 - 4.2%↑, B10 - 5%↑) were measured. Likewise, emission parameters such as CO (B5 - 0.02%↓, B10 - 0.04%↓), HC (B5 - 1 PPM↓, B10 - 5 PPM↓), NOx (B5 - 20 PPM↓, B10 - 89 PPM↓), and CO2 (B5 - 0.3%↑, B10 - 0.4%↑) are measured by using AVL Di-gas analyzer. It was noticed that increased peak cylinder pressure and greater heat release rate were on account of a longer ignition delay period. Additionally, an increase in engine performance and the corresponding reduction in exhaust emission have also been observed upon using aloevera-emulsified diesel fuel.

Comparative analysis of different heat transfer models, energy and exergy analysis for hydrogen-enriched internal combustion engine under different operation conditions

The implementation of hydrogen as a fuel in internal combustion engines is widely considered a favorable optimal due to its zero-carbon emissions and high energy content. Heat transfer from engine cylinder walls has a major role on engine combustion, performance and emission characteristics. In this study, heat transfer analysis conducted by different heat transfer models and identify the best model to analyse the energy and exergy analysis of hydrogen enriched internal combustion engine. A series of experiments were conducted on a compressed natural gas internal combustion engine across varying hydrogen fractions, EGR ratios, engine speeds and load conditions to capture in-cylinder pressure data and heat transfer rate. The authors compared six distinct models for heat transfer based on absolute percentage errors of maximum pressure and indicated mean effective pressure. These models systematically incorporated into a quasi-dimensional combustion model (QDCM) on MATLAB for hydrogen-compressed natural gas engine, accounting for diverse operating conditions. Convective heat transfer models, including Woschni, Nusselt, Hohenberg, Han, Eichelberg, and Assanis correlations were employed. Comparative analyses were undertaken to identify the most precise correlation for predicting engine in-cylinder pressure and heat transfer rates with experimental results across a broad spectrum of operational conditions. The Woschni model, as presented, is most suitable for the QDCM of the hydrogen-compressed natural gas fuel blend. This suitability is indicated by the close alignment of Taylor length and turbulent intensity coefficients to 1, as well as the minimal absolute percentage error observed for indicated mean effective pressure. It is also observed that heat transfer rate is increased by increasing the engine load 25 %, 50 %, 75 % and 100 % as 49.57 J/deg, 129.26 J/deg, 245.35 J/deg and 250.62 J/deg respectively and heat transfer rate is decreased by increasing the speed of engine 1100 rpm, 1200 rpm, 1500 rpm and 1700 rpm as 137.34 J/deg, 134.21 J/deg, 95.33 J/deg and 48.57 J/deg respectively. The energy and exergy analyses revealed that elevating the engine load corresponds to a reduction in exergy destruction. Brake energy increased 15 % by increasing the load conditions from 25 % to 100 % and decreased 7 % by increasing the speed from 1100 rpm to 1700 rpm. Another significant finding from this study is that the values of both energy and exergy efficiencies were 38.42 % and 40.12 % respectively obtained by thermodynamic analyses.

A Review of Recent Advancements in Knock Detection in Spark Ignition Engines

In gasoline engines, the combustion process involves a flame’s propagation from the spark plug to the cylinder walls, resulting in the localized heating and pressurization of the cylinder content ahead of the flame, which can lead to the autoignition of the gasoline and air. The energy release from the autoignition event causes the engine cylinder to resonate, causing an unpleasant noise and eventual engine damage. This process is termed as knock. Avoiding knock has resulted in limiting the maximum engine pressures, and hence limiting the maximum efficiencies of the engine. Modern engines employ knock sensors to detect resonances, adjusting the spark plug timing to reduce pressures and temperatures, albeit at the expense of engine performance. This paper sets out to review the different signals that can be measured from an engine to detect the start of knock. These signals traditionally consist of the in-cylinder pressure, the vibrations of the engine block, and acoustic noise. This paper reviews each of these techniques, with a focus on recent advances. A number of novel methods are also presented, including identifying perturbations in the engine speed or exhaust temperature; measuring the ion charge across the spark plug leads; and using artificial intelligence to build models based on engine conditions. Each of these approaches is also reviewed and compared to the more traditional approaches. This review finds that in-cylinder pressure measurements remain as the most accurate for detecting knock in modern engines; however, their usage is limited to research settings. Meanwhile, new sensors and processing techniques for vibration measurements will more accurately detect knock in modern vehicles in the short term. Acoustic measurements and other novel approaches are showing promise in the long term.

Performance and emission analysis of hydrogen-fuelled compression ignition engine with EGR: a prospective approach towards clean mobility

The energy demand has still been fulfilled, primarily by fossil fuels globally. Hydrogen is the only carbonless fuel that can fulfil the energy demand without impacting the environment. In this research work, a variable compression ratio (VCR) CI engine with exhaust gas recirculation (EGR) is tested with hydrogen gas as a primary fuel. Initially, the diesel is used as a pilot fuel igniter to initiate the combustion process. Once the cycle is initiated, the hydrogen gas is supplied and controlled through port fuel injection at a pressure of 2 bar. The engine is operated at various compression ratios (12, 14, 16, 18) and different loads: 0% (0 kg), 25% (4 kg), 50% (8 kg), 75% (12 kg) and full load (16 kg), with and without exhaust gas recirculation. The results revealed that the brake thermal efficiency of the hydrogen-fuelled engine increased by 6.5% and a significant decrement in brake-specific fuel consumption (bsfc). The maximum cylinder pressure inside the cylinder is observed at 68 bar at 12 kg of load and 18 CR. The NOx emission is reduced by 49.4% by using the cold ERG method.

Health monitoring of in-cylinder sensors and fuel injectors using an external accelerometer

This paper focuses on the development of a methodology to monitor the health of an engine by detecting any failures in the fuel injectors or in-cylinder pressure sensors using an accelerometer that is non-intrusively mounted on the engine block. A multi-cylinder engine with each cylinder having its own pressure sensor and injector is considered. First, a model relating the combustion component of the measured acceleration signal to the combustion component of in-cylinder pressure is proposed. Then, gains of the model are tuned to reduce the cycle-to-cycle estimation error by analyzing cycle-to-cycle variations with respect to the combustion pressure peak and engine vibration peak. Using the developed model, cylinder combustion pressures are estimated from engine vibration signals with small cycle-to-cycle estimation errors. Subsequently, a health monitoring system that can detect faults in pressure sensors, fuel injectors, and the accelerometers is proposed based on residues obtained from the difference between estimated combustion pressure and measured pressure signals. The source of the failed component can be identified uniquely by analyzing the pattern of residues. The proposed combustion pressure estimation algorithms are validated by extensive evaluation with experimental data obtained by operating a four-cylinder compression-ignition direct-injection engine with a range of experimental data. Finally, the developed health monitoring system is evaluated with various failure scenarios involving faults in the in-cylinder pressure sensor, fuel injector, and accelerometer.

Impact of fuel injection parameters and hydrogen enrichment on CI engine characteristics fueeled with Ceiba pentandra biodiesel

ABSTRACT Alternative fuel resources are currently gaining popularity as a potential solution to the challenges caused by a shortage of petroleum fuels and the associated increase in environmental pollution. Hydrogen (H2) as an alternative fuel source is getting a lot of attention. The motivation of this research was to examine how the fuel injection parameters (FIP) and H2 enrichment influence CI engine features when blended with Ceiba pentandra biodiesel. Based on the findings of prior research work, a 20% biodiesel blend (B20) and optimal FIP of 260 bar and 27° BTDC were selected for this trial, along with 10 lpm of H2 enrichment. As compared to diesel at standard FIP, the synergistic action of B20 with H2 enrichment and optimum FIP achieved the goal of improving performance and combustion, leading to increased brake thermal efficiency (10%), cylinder pressure (5%), and heat release rate (7.4%) while reducing brake-specific fuel consumption (9%) and emitting lesser emissions of hydrocarbon (16%), carbon monoxide (12%), and smoke (18%) emissions than diesel, except Nitrogen oxides. Therefore, combining these two strategies of optimum FIP and H2 enrichment with novel Ceiba pentandra biodiesel blend opens the door to a healthier ecosystem with superior combustion and lesser emission.

A Pressure-Oscillation-Based RON Estimation Method for Spark Ignition Fuels beyond RON 100

Knock in spark ignition (SI) engines occurs when the air–fuel mixture in the combustion chamber ignites spontaneously ahead of the flame front, reducing combustion efficiency and possibly leading to engine damage if left unattended. The use of knock sensors to prevent it is common practice in modern engines. Another measure to mitigate knock is the use of higher-octane fuels. The American Society for Testing and Materials’ (ASTM) determination of the Research Octane Number (RON) and Motor Octane Number (MON) of spark ignition fuels has been based on measuring cylinder pressure rise at the onset of knock since its inception in the 1930s. This is achieved through a low-pass filtered pressure signal. Knock detection in contemporary engines, however, relies on measuring engine vibrations caused by high-frequency pressure oscillations during knock. The difference between conditions in which fuels are evaluated for their octane rating and the conditions that generate a knock intensity signal from the knock sensor suggests a potential difference between octane rating and the knock limit typically identified by a contemporary knock sensor. To address this disparity, a modified RON measurement method has been developed, incorporating pressure oscillation measurements. This test method addresses the historical lack of correlation between RON and high-frequency pressure oscillation intensity during knock. Using toluene standardization fuels (TSFs) as a reference, the obtained results demonstrate excellent high-frequency knock intensity-based RON estimations for gasoline. The method is able to differentiate between two fuels that share the same ASTM RON, associating them with a RON-like metric that is more aligned with their performance in a modern SI engine. This alternative method could potentially serve as a template for an upgrade to the existing ASTM RON method without significantly disrupting the current approach. Additionally, its capability to evaluate fuels beyond RON 100 opens the door to assessing a wider range of fuels for antiknock properties and the intensity of fuel oscillations during knocking combustion.

A Multifactor Combination Optimization Design Based on Orthogonality for a Two-Degree-of-Freedom Floating Machine Gun Vibration System

This paper introduces a novel type of floating machine gun that can be simplified as a self-balancing two-degree-of-freedom mechanical system with distinct vibration characteristics. The model accounts for intricate motion patterns and encompasses numerous potential influencing factors. Multifactor combination optimization of the system represents a pressing engineering challenge. After establishing a simulation model for the machine gun and validating it experimentally, seven factors were chosen as optimization variables. The maximum recoil displacement of the inner receiver (MRD) and the firing rate were chosen to be indicators. Orthogonal combinations and variance analyses were used, and the effects of multiple factors were analyzed using SPSS software; these processes led to a determination of the optimal combination. The results indicated that the piston cylinder pressure, the bi-directional buffer spring energy storage, and the inner receiver mass significantly affected the MRD. Furthermore, the automaton mass and the reset spring energy storage were found to substantially affect the firing rate. Careful analysis of the variance results facilitated the determination of the optimal combination of parameter values. Remarkably, the optimal combination chosen resulted in an MRD reduction of approximately 20.2% and a firing rate increase of approximately 26.6%.