Automotive Engine Research Articles

Adaptive Design of Experiments for Automotive Engine Applications Using Concurrent Bayesian Optimization

Abstract Most practical automotive problems require the design of experiments (DoEs) over a number of different operating conditions to deliver optimal calibration parameters. DoE is especially crucial for automotive engine calibration problems due to its increasing complexity and nonlinearity. As the complexity of the system increases, the DoE applications require a significant amount of expensive testing. However, only a limited number of testings are available and desired. The current work addresses this issue by presenting an adaptive DoE method based on Bayesian optimization to find optimal parameter settings with a significantly reduced number of physical testings (or function evaluations). To further improve optimization efficiency, this work presents a new approach: concurrent Bayesian optimization, which searches for optimal DoE under multiple operating conditions simultaneously. The method utilizes a surrogate model and a novel concurrent evolutionary multi-objective optimization method: concurrent non-dominated sorting genetic algorithm-II, to solve adaptive DoE in multiple operating conditions with a limited number of function evaluations. The experimental study is carried out on a gasoline engine calibration problem using a high-fidelity GT-SUITE™ engine model. The experimental results demonstrate the effectiveness of the algorithm by optimizing engine performance with a significantly reduced number of expensive testings to achieve accurate optimal solutions. The method simultaneously performs engine calibration at eight different operating conditions using only 500–600 testings, compared to the traditional approach, where each operating condition requires 300–500 testings independently to achieve optimal results.

Semi-Active Controllable Stiffness Engine Mount Utilizing Natural Rubber-Based Magnetorheological Elastomers

This study proposes the design and fabrication of a natural rubber-based magnetorheological elastomer (NR-MRE) engine mount as a new device in absorbing the vibration originated from the automotive engine. The conceptual design was performed through a simulation process by Finite Element Method Magnetics to analyze the magnetic field distribution. The simulation result had indicated that the device was capable of generating an equivalent magnetic field density of 0.31 T at the effective area. The MRE was prepared by utilizing 60 wt% of carbonyl iron particles (CIPs), and the cavity was filled by compression molding. The MRE compound was tested based on its basic mechanical properties, while the MRE engine mounts were tested under a static compression load at off- and on-state conditions. It was observed that the compound possessed a good tensile strength for a load bearer matrix with an average of 12.65 MPa. Subsequently, the results of the static compression load had showed that the MRE engine mounts recorded an increase of 12% in the force generated as compared to conventional engine mounts at an off-state condition. Meanwhile, at an on-state condition of 2.4 A, the MRE engine mounts recorded an increase in the force generated with 106%. The study has demonstrated that the proposed device can be one of the potential candidates for vibration control applications due to its stiffness controllability.

WEDM of Al/SiC/Ti composite: A hybrid approach of RSM-ARAS-TLBO algorithm

Aluminum-based hybrid composites are the lightweight materials used for many industrial applications. These applications include brake parts, automotive engine, high speed rotating shafts, high speed machinery and robots. The machining of aluminum was normally done by conventional machining processes. However, after the addition of ceramic particles, it became difficult to process the hybrid composite by conventional processes. Thus, non-conventional machining processes are used for the machining of aluminum-based hybrid composite. In the present work, the aluminum-based hybrid composite was developed using stir casting method, where Al6063 was used as matrix material and SiC along with Ti were used as reinforcement material. After the development of hybrid composite, the material is processed on wire electric discharge machining (WEDM). The varying control factors while machining was pulse on-time (Ton), pulse off-time (Toff), servo voltage (SV) and wire feed (WF). However, the response variable to measure the machining characteristics were cutting speed (CS) and kerf width (KW). The experiments were planned according to Response Surface Methodology (RSM) based Box Behnken Design (BBD). The response variables were converted into optimality function using Additive Ratio Assessment (ARAS) and then the developed empirical model was solved by Teaching Learning Based Optimization (TLBO). The optimized setting suggested by hybrid approach is Ton: 128 μs; Toff: 48 μs; SV: 48 V; WF: 7 m/min. After the optimization an improvement of 12% in optimality function, 18.24% in CS and 17.11% in KW was observed as compared to the best experimental run. The morphological investigation shows that at the optimized setting the presence of micro-cracks, sub-surface, globules and recast layer reduced significantly.

Chemically cross-linked gel storage for fuel to realize evaporation suppression

High-energy density liquid fuels are commonly used to operate combustors such as rockets, gas turbines, automotive engines, and boilers to make an energy transformation. To prevent a serious incident such as an explosion or a fire disaster, we have recognized practical issues of the liquid fuels that are safety and stability during transportation and storage, evaporation rate, and burning rate constant. In this experiment, ethanol is used as a liquid fuel and is retained on chemically cross-linked poly(N-isopropylacrylamide) (PNIPPAm) gel to use it as a polymeric gel storage for liquid fuels. In general, because the cross-linking structure of chemical gels is formed by covalent bonding, it is more stable than physical gels for a thermodynamic change such as temperature. The evaporation rate of the polymeric gel storage to suppress evaporating the ethanol is investigated. We finally demonstrate to obtain burning rate constants based on a changing mass of the polymeric gel storage during combustion. By demonstrating the polymeric gel storage combustion, we revealed existence of the d2 law in a droplet combustion.

Technical Analysis on Reducing Automotive Engine Emissions

Technical Analysis on Reducing Automotive Engine Emissions

Tribological and mechanical characterization of as-cast and thermal treated Al-9Si/SiC graded composite

Tribology and mechanical properties of thermal treated Al-9Si/10wt%SiC functionally graded composite are compared with as-cast condition. The composite was centrifugally cast as a hollow cylindrical component (Ø(outer) 100 × Ø(inner) 60 × 100 mm), characterized at three wall layers (up to 3, 10, and 18 mm) from the outer periphery. Metallographic analysis on as-cast composite and thermal treated components revealed graded structure and spheroidization of acicular Si, respectively. Elemental mapping and phase formations were confirmed through Energy-dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD) analysis. Outer layer of thermal treated component revealed maximum improvement in hardness (26%) and tensile strength (15%) compared to as-cast. Brittle mode of failure was featured through fractography. A combination of adhesive and abrasive mechanisms were predominant during reciprocating wear. EDS analysis of wear debris formed at intermediate sliding distance (1250 m) confirmed the oxide layer formation. Thus, the thermal treated composites are developed for automotive engine components vulnerable to wear.

Fiber-optic Michelson interferometer for detecting coolant level and refractive index

Abstract This paper presents an interferometer based on a single-mode fiber-multimode fiber-thin-core fiber (SMF–MMF–TCF) Michelson interference structure that can be used for the measurements of coolant level and refractive index. Because of the different diameters of the cores of the individual fibers, optical excitation and coupling occur at the splicing points of the fibers. The multimode fibers are the couplers in the sensing structure, which allow the exciting light to enter the cladding of the thin-core fibers. The end face of the thin-core fiber is coated with a silver film to enhance the reflectivity of the light. The results show that the interference intensity first increases and then decreases with the length of TCF. When TCF is 4 cm, the interference light intensity is the strongest. The sensitivity of the sensor is 138.091 nm/RIU with the linearity of 0.977 over the refractive index of the coolant in the range of 1.3605–1.3880, and the temperature and time effects on the sensor are small. The proposed sensor has the advantages of simple fabrication, high repeatability, and good stability and it can be applied to the measurements of coolant level and refractive index in automotive engines.

Experimental investigation on effects of equivalence ratio on combustion with knock, performance, and emission characteristics of dimethyl ether fueled CRDI compression ignition engine under homogeneous charge compression ignition mode

This study deals with the effects of different equivalence ratios on combustion with a knock, performance, emissions of a DME fueled automotive CI engine under HCCI mode. The conventional common rail direct injection (CRDI) CI engine was modified to run with DME fuel (manifold injection) under HCCI mode. The experiments were conducted on the engine at different equivalence ratios at a constant speed of 1400 rpm. Two stages of combustion (low-temperature reaction (LTR) region and high-temperature reaction (HTR) region) were observed under HCCI mode. The LTR region occurs at the temperature range from 700 to 750 K. In contrast, the HTR region was at a temperature beyond 1000 K. The cyclic variations with the coefficient of variation (COV) of maximum in-cylinder pressure, indicated mean effective pressure with knock peak pressure and knocking intensity (KI) were analyzed for assessment of combustion stability. Based on the knocking intensity, the optimum equivalence ratio with controlled auto-ignition (CAI) was found as 0.55, with peak in-cylinder pressure of 70.87 bar and peak in-cylinder temperature of 1815 K. The COV for all the parameters and KI found below the limit value (COVlimit − 5% and knocklimit − 5 MW/m2) till 0.55 equivalence ratio and beyond the equivalence ratio, the knock occurred resulting in uncontrolled auto-ignition (UAI). Ultra-Low NOx (10–15 ppm) and zero smoke emissions with a considerable reduction in CO and HC emissions were observed at a higher equivalence ratio from DME fueled HCCI mode. However, CO and HC emissions were higher at lower equivalence ratio. This study shows that the simultaneous reduction of NOx and smoke emissions could be achieved in a DME fueled HCCI engine.

Experimental investigations of effects of cycle time on NOx emission in a hydrogen fueled multi-cylinder automotive spark ignition engine

The present study deals with the influence of cycle time on NOx emission in a hydrogen-fueled multi-cylinder automotive spark-ignition engine. The engine was operated at a constant torque of 70 Nm in the speed range of 1000–1900 rpm with a step interval of 300 rpm. FT-IR spectrometer was used to measure the real-time regulated (NO, NO2) and non-regulated (N2O, HCN) emissions. The peak in-cylinder pressure and convective heat transfer rate decreased till cycle time of 75 ms due to reduced available time for combustion and heat exchange resulting in lower NO emission. However, as the cycle time decreased to 63 ms, NO emission shot up. NO emission drastically increased about five times higher at an engine speed of 1900 rpm compared to lower engine speeds due to an increase in peak in-cylinder gas temperature (above 1700 K). Percentage apportionment of NO2 to NOx emission is by half at 1900 rpm due to the rise of NO emission at higher engine speeds. The increasing trend of HCN and NMHC emissions with engine speed indicates the possibility of lubricating oil burning.

Pentanol/diesel fuel blends: Assessment of inhalation cancer risk and ozone formation potential from carbonyl emissions emitted by an automotive diesel engine

Pentanol has recently drawn particular attention as a fuel for diesel engines due to its higher energy density and its renewable nature. However, it is well known that oxygenated fuels increase carbonyl emissions, that are harmful to human health. In this study, carbonyl compounds emitted by an automotive diesel engine fueled with pentanol and ultra-low sulfur diesel (ULSD) blends were investigated. Three ULSD-pentanol blends were studied: 13%, 15.5% and 20% by volume. A common-rail, direct-injection diesel engine equipped with exhaust gas recirculation system and diesel oxidation catalyst was operated under two representative urban driving modes (M1: 1750 rpm and 71Nm; M2: 2450 rpm and 90Nm). Carbonyls were sampled from the undiluted exhaust by trapping the gas with 2,4-DNPH cartridges and analyzed by HPLC-UV. The impact of carbonyl specific emissions on the ozone formation potential (OFP in mg O3/kWh) was determined and their estimated inhalation cancer risk (CR) associated with carcinogenic compounds such as formaldehyde and acetaldehyde were quantified. Results indicate that total specific carbonyl emissions increased significantly with pentanol addition, and a maximum was observed with the 15% blend for both engine operating modes. The emissions of all measured carbonyls decreased for the high engine load. Formaldehyde, acetaldehyde, acetone and acrolein were the most abundant carbonyls independently of the fuel tested. The OFP increased with pentanol blends by up to a factor of 2 for M1 and 4 for M2. The estimated inhalation CR increased up to 5x with pentanol blends for a specific exposure scenario evaluated. According to the results obtained in this work, the CR are below the threshold suggested U.S EPA, however, the CR were calculated considering two relevant aldehyde compounds. To reach a representative cancer risk assessment, the greatest possible quantity of carcinogenic volatile organic compounds (VOCs) should be measured.

Spray Characteristics of Bioethanol-Blended Fuel under Various Temperature Conditions Using Laser Mie Scattering and Optical Illumination

Bioethanol has great potential to reduce emissions from transportation while improving energy security and developing the economy. Bioethanol has a higher octane-number and a higher enthalpy of vaporisation than gasoline (resulting in charge cooling)—properties that have been used to extend knocking limits. Therefore, bioethanol can be used to substitute gasoline in automotive engine applications. The characteristics of bioethanol spray, such as hydrous bioethanol fuel which consists of 93% bioethanol and 7% water, were investigated under various temperature conditions from sub-zero (−15 °C) to room temperature (17 °C) by means of high-speed direct photography and laser Mie scattering techniques without any seeding materials. The experimental results show that the spray patterns are not significantly changed. In the case of the sub-zero temperature condition, the spray tip penetration decreases while the spray angle keeps almost constant once the spray becomes fully developed. The results show that scaling of the spray tip penetration rate achieves a reasonable collapse of the experimental results. The normalised droplet diameter was also obtained and shows that larger droplets are formed at the sub-zero temperature condition.

Possibility of reducing the technogenic load on the environment by reducing oil waste in diesel

The study is aimed at solving an important environmental problem of reducing the technogenic load on the environment created by automotive diesel engines. The issue of reducing the toxicity of exhaust gases by reducing the waste of oil in the combustion chamber of the cylinder-piston group for various modifications of 15/18 diesel engines is considered according to the results of bench tests. It was found that a decrease in oil burnout in a diesel engine is accompanied by a decrease in CO, CH, PM emissions with exhaust gases. At the same time, a slight increase in emissions of nitrogen oxides NOx was observed. It was found that with a change in oil burnout from 0.32 to 0.6% of fuel consumption, the estimated indicator for nitrogen oxides decreased by 10%, for carbon monoxide - increased by 52%, for hydrocarbons - increased by 50%, for solid particles - increased by 94%. The results of the study showed that the technogenic load matters. The indicator of technogenic load was HTL = 43.63 tl/g with oil burnout of 0.32% and HTL = 39.87 tl/g with oil burnout of 0.6% due to reduction of NOx emissions.

An Evaluation of an Unhealthy Part Identification Using a 0D-1D Diesel Engine Simulation Based Digital Twin

<div class="section abstract"><div class="htmlview paragraph">Commercial automotive diesel engine service and repair, post a diagnostic trouble code trigger, relies on standard troubleshooting steps laid down to identify or narrow down to a faulty engine component. This manual process is cumbersome, time-taking, costly, often leading to incorrect part replacement and most importantly usually associated with significant downtime of the vehicle. Current study aims to address these issues using a novel in-house simulation-based approach developed using a Digital Twin of the engine which is capable of conducting in-mission troubleshooting with real world vehicle/engine data. This cost-effective and computationally efficient solution quickly provides the cause of the trouble code without having to wait for the vehicle to reach the service bay. The simulation is performed with a one-dimensional fluid dynamics, detailed thermodynamics and heat transfer-based diesel engine model utilizing the GT-POWER engine performance tool. The prediction accuracy of the engine model is validated against a standard duty cycle data from engine testing. Multiple failure modes listed in the service troubleshooting steps for several diagnostic trouble codes are then incorporated in the engine model. Some examples of failure modes include, leakage in the plumbing of engine flow path, restricted air-filter, failed actuators, degraded heat exchanger performance etc. When a diagnostics trouble code is triggered on a vehicle, the Digital Twin simulation model initiates a design of experiment (DOE)-based analysis of associated failure modes and their different levels of failure, using a few minutes of engine transient cycle data as inputs. A set of performance parameters predicted from the model are extracted for each DOE experiment and using the same parameters from the engine data as reference, an error metric is computed for the duration of the duty cycle. This error metric is used to compare the various failure modes which are then ranked as an indicative of their closeness to the engine data. Failure modes which are responsible for the diagnostic trouble code, will tend to have a lower value of the error metric while the ones in healthy state on the real engine will be insensitive to the engine data. The Digital Twin model has been validated with real world customer truck data where the prediction of the model is compared to actual service troubleshooting results. Over multiple occasions, the Digital Twin model has been able to not only strongly indicate the actual failure, but also eliminate failure modes which are insensitive to the engine data for the trouble code. This is expected to be an assistive service tool where a robust, highly accurate, predictive and a computationally efficient simulation is run in the background whenever an engine sees an issue with performance or indicates any unhealthy characteristics. Moreover, since the simulation is capable of being run in-mission, the service technician can be alerted with indicative part failure of the vehicle even before the vehicle reaches the service bay, such that they can be prepared with appropriate maintenance actions and order parts that need replacement. This will result in a drastic reduction in vehicle downtime and cost associated with each service event.</div></div>

DRIVEABILITY INDEX OF COMMERCIAL GASOLINE IN ASEAN COUNTRIES

Motor gasoline is essentialy a complex mixture of hydrocarbons distilling between about 40°C and 225°C and consisting of compounds generaly in the range C5 to C12. Small amounts of additives are also used to exchange various aspects of the performance of the fuel. Gasoline produced from different refin[1]eries can vary widely in compositions, even at the same octane level.The primary requirement of a gasoline is that should burn smoothly without exploding, under the conditions existing in the combustion chamber of the spark-ignition, so that themaximum amount of useful energy is liberated[1].The volatility of a gasoline has a vital influence on the both performance of a car emission. It affects the way car starts, the time it takes to warm up, the exten to which ice will form in the carburator, causing stalling and other problems; it influences vapour lock in the fuel system and indirectly it determines overall fuel economy. Volatility is a measure of the ability of a fuel to pass from the liquid to the vapour state under varying conditions.In cold weather, cars can take a very significant time to warm-up i.e., be capable of smooth, non-hesitating accelerations without the use of the choke. The fuel parameter that is found to have the grestest influence on warm-up is the mid-boiling range volatility as characterized by for example; the 50 per cent distillation temperature. Even after the car has warmed up, fuel volatility can still have an influence on acceleration time. Low volatility fuels obviously give leaner mixture and as mixtures leaner, acceleration performance can fall off quite rapidly.The fraction of the fuel that influences acceleration behaviour to the greatest extent is in the mid and to a lesser extent the higher boiling range. Thus, the 50% distillation temperature, sometimes together with the 90% distillation, must be controlled to ensure optimum acceleration behaviour. The factors which influence vapour lock is the volatility characteristics of the fuel. The degree to which a fuel is liable to give vapour lock depends mainly on its front end volatility. A number of different front-end volatility parameters have been used to define the vapour locking tendency of a fuel, such as RVP, percentage evaporated at 70°C, the 10 and 15% slope of the distillation curve, the vapour/liquid ratio at a given temperature and pressure. These distillation characteristics affect the following performance characteristics: starting, vapour lock and driveability.ASTM D4814-98a the standard specification for Automotive Spark-Ignition Engine Fuel has included Driveability Index as an item of performance requirement of the fuel. The inclusion of the parameter is to provide control of distillation parameters that influence cold start and warm up driveabilities.

Estimation of the performance of automotive engines by the results of their diagnosis under operating conditions

The need for food supply for the population has been and remains the most important component of the life of the world's population. In connection with the growth of the population, this need will grow. Considering that food production requires enormous and constant work in the bosom of the Earth's biosphere, measures are being taken to alleviate working conditions, increase its efficiency, safety and efficiency. In this regard, the growth of electromechanization and automation of technological processes in the agro-industrial complex is an inevitability not only of the past, but also of the current century. With regard to agricultural production, the decisive factor in this direction is the use of mobile agricultural units with piston motor tractor engines. The latter are characterized by the peculiarity of reducing efficiency as they approach the amortization period, up to complete failure (i.e., termination of performance). In this regard, specialists are developing methods and tools for diagnosing the operability of auto-tractor engines in order to restore it in a timely manner. For this purpose, an innovative device has been proposed for diagnosing the operability of these engines. The article provides a diagram of the device, a description of the principle of its operation to achieve the set goal under operating conditions. The constituent structural elements of the device are deficient-free and affordable. The device combined with their use is not structurally difficult and allows one to obtain reliable results on assessing the performance of engines according to their measured characteristic indicators under operating conditions.

Wear Study of Cubic Boron Nitride (cBN) Cutting Tool for Machining of Compacted Graphite Iron (CGI) with Different Metalworking Fluids

Due to its desirable mechanical properties, compacted graphite iron (CGI) has been used to replace conventional gray cast iron (CI) in various applications, such as automotive engine blocks and cylinder heads. However, the poor machinability of CGI can lead to excessive tool wear and consequently high manufacturing costs. Various strategies have been developed to improve the machinability of CGI, including optimizing machining parameters and the development of novel metalworking fluids. In this study, machining of CGI was conducted using cubic boron nitride (cBN) tools under different cutting speeds, with both soluble and full-synthetic water-based metalworking fluids at different levels of sulfur addition and water dilution. The effects of the metalworking fluids on the tool wear behavior were examined. Results showed that at 200 m/min cutting speed, the soluble metalworking fluid at 4% dilution and 0.3% sulfur compound exhibited the best performance, with a cutting distance reaching 23.8 km. In contrast, the least effective soluble metalworking fluid at 9% dilution and 0.3% sulfur compound resulted in a 28.6% decrease in the cutting distance (17.0 km) compared to the best one. At a higher speed (300 m/min), the cutting distance for all metalworking fluids dropped to less than 6.0 km, with the full-synthetic metalworking fluid showing the shortest cutting distance of 4.8 km.

Exhaust Gas Temperature Pulsations of a Gasoline Engine and Its Stabilization Using Thermal Energy Storage System to Reduce Emissions

Modern automotive gasoline engines have highly efficient after-treatment systems that reduce exhaust gas emissions. However, this efficiency greatly depends on the conditions of the exhaust gas, mainly the temperature and air–fuel ratio. The temperature instability during transient conditions may cause a reduction in the efficiency of the three-way catalyst (TWC). By using a thermal energy storage system before TWC, this negative effect can be suppressed. In this paper, the effects of the temperature stabilization on the efficiency of the three-way catalyst were investigated on a 1-D turbocharged gasoline engine model, with a focus on fuel consumption and emissions. The thermal energy storage system (TESS) was based on PCM materials and was built in the exhaust between the turbine and TWC to use the energy of the exhaust gas. Three different materials were picked up as possible mediums in the storage system. Based on the results, the usage of a TESS in a gasoline after-treatment system has shown great potential in improving TWC efficiency. This approach can assist the catalyst to operate under optimal conditions during the drive. In this study, it was found that facilitating the heat transfer between the PCM and the catalyst can significantly improve the emissions’ reduction performance by avoiding the catalyst to light out after the cold start. The TESS with PCM H430 proved to reduce the cumulative CO and HC emissions by 8.2% and 10.6%, respectively, during the drive. Although a TES system increases the after-treatment cost, it can result in emission reductions and fuel consumption over the vehicle’s operating life.

Performance Evaluation of a Single Cylinder Compressed Air Engine: An Experimental Study

Abstract The quest to reduce dangerous environmental emissions has led to the research and use of alternate and renewable energy sources. One of the major contributors to the dangerous environmental emissions is the automotive industry. The world is, therefore, quickly moving towards hybrid and electric vehicles. An alternate pollution-free automotive engine is a compressed-air engine, which is powered by compressed air and is more efficient than the electric engine since it requires less charging time than a traditional battery-operated engine. Furthermore, the tanks used in compressed-air engines have a longer lifespan in comparison to the batteries used in electric vehicles. However, extensive research is required to make this engine viable for commercial use. The current study is a step forward in this direction and shows the performance analysis of a single-cylinder compressed-air engine, developed from a four-stroke, single-cylinder, 70 cc gasoline engine. The results show that compressed-air engines are economic, environmental friendly and efficient.

Cycle-to-cycle combustion analysis in hydrogen fumigated common-rail diesel engine

An experimental cycle-to-cycle analysis in multi-cylinder automotive common-rail compression ignition engine was performed to understand better the combustion in the hydrogen fuelled diesel engine. Hydrogen was fumigated in intake line at a wide-ranging from 0 lpm to 50 lpm in steps of 10 lpm. Test engine was operated at three different loads for a constant engine speed. The relative air–fuel ratios were between 1.55 and 3.31. The combustion occurred with an excess of air in all tests. Combustion data of 120 cycles were used to analyse the cyclic variations, determined by standard deviation of the cylinder pressure. Cyclic variations, coefficient of variance (CoV), standard deviation, frequency, and average value of peak combustion pressure (Pmax), maximum pressure rise rate (PRRmax), indicated mean effective pressure (IMEP), mass fraction burned (MFB), and MFB10-90 duration were analysed. Results showed that for all hydrogen addition levels, CoVs of Pmax, IMEP and MFB10-90 were always found below 3% at all loads, and PRRmax values with hydrogen operations in each cycle were under the limit of knocking combustion. Engine load was the most important factor to affect to CoV, standard deviation, and frequency of the combustion parameters. Minor cyclic variations in MFB traces were found at all engine loads and hydrogen addition levels, which agreed well with the cylinder pressure traces. Frequencies of Pmax and IMEP were moderate in low and medium loads, but reduced in high load, and also the values of Pmax and IMEP in high load were distributed in a wider range compared to low and medium loads. MFB10-90 duration increased for dual-fuel modes, its frequency was decreased, and its distribution was extended with hydrogen addition. Trend of standard deviation was mostly similar to that of CoV for the studied combustion parameters. Furthermore, variations of correlation coefficient (R) among Pmax, PRRmax, IMEP, and MFB10-90 were discussed in this paper, and the highest R value was found between IMEP and Pmax.

Investigation of bifurcations in cyclic combustion dynamics of a CNG-diesel RCCI engine

This study uses nonlinear dynamical and chaotic methods to investigate the cyclic combustion dynamics of a CNG-Diesel reactivity control compression ignition (RCCI) engine. The experiments of RCCI combustion mode are conducted on a single-cylinder automotive diesel engine with the development ECU. Low reactivity fuel (i.e., CNG) is injected into the intake manifold, and high reactivity fuel (i.e., diesel) is injected directly into the engine cylinder during the RCCI experiments. Mass of fuel injection per cycle and their injection events are controlled by using ECU. The engine is tested for fixed engine load and speed of 3 bar BMEP and 1500 rpm, respectively. A double diesel injection strategy is used for injecting the diesel fuel into the engine cylinder. In-cylinder pressure is measured using a piezoelectric pressure transducer on a crank angle basis with a resolution of 0.1 CAD. Combustion parameters are calculated on a cyclic basis from measured in-cylinder pressure. In this study, the effect of diesel injection timing (SOI-2) on the behavior of combustion dynamics for two different masses of port-injected CNG fuel (mc) is investigated. The CA50 time series of 1000 consecutive engine cycles is analyzed for combustion dynamics analysis using symbol sequence analysis, return maps, recurrence plots (RPs), recurrence quantitative analysis (RQA), and 0–1 test. The peaks in symbol sequence histograms and the corresponding symbol series depict the period-2 nature of the cyclic combustion dynamics at the intermediate SOI-2 of 30° and 40° bTDC. Return maps also confirm the onset of noisy period-2 bifurcation at 30° bTDC SOI-2. The dominance of deterministic period-2 characteristics is found in the cyclic combustion dynamics at 30° and 40° bTDC SOI-2 using recurrence plots. The 0–1 test method depicts stronger chaotic cyclic combustion dynamics at 20° and 50° bTDC SOI-2. In summary, the present study supports the existence of a periodic window in between the chaotic combustion for the intermediate values of SOI-2. The dominance of the deterministic characteristics makes this regime of intermediate SOI-2 values suitable for a better cycle resolved control.