In-cylinder Air Research Articles

INVESTIGATION OF GUIDE VANE SWIRL AND TUMBLE DEVICE TO IMPROVE IN-CYLINDER AIR FLOW FOR COMPRESSION IGNITION ENGINE RUNNING WITH BIODIESEL

Biodiesel is expected to become the main alternative fuel for transportation purposes in the coming future as a result of the recession of crude oil. The main advantage that makes biodiesel the first choice as a substitute for petroleum-based fuel is that biodiesel can be used in a compression ignition engine (CI) with minor modification. Unfortunately, with biodiesel, the engine experiences reductions in power and torque, and increases in fuel consumption and carbon deposits inside the combustion chamber mainly due to lower calorific value and heavier molecules present in the biodiesel. One of the solutions to minimize this problem is to increase the in-cylinder air motion and use this to break up the heavier molecules and mix these molecules with air. To achieve this, a high turbulent flow is required inside the cylinder. This paper presents the model of the Guide Vane Swirl and Tumble Device (GVSTD) to develop an organized in-cylinder turbulent flow. The basic model of GVSTD consists of simple fins imposed inside the intake system. Through computer simulations, the results of air flow characteristics are compared with a conventional intake system. The height of GVSTD vanes was varied at 25%, 50% and 75% of the intake runner radius. The results show that in-cylinder velocity, turbulence kinetic energy and absolute pressure at the start of the injection increase around 41%, 6% and 3%, respectively more than the ordinary system which is expected to improve the mixing of biodiesel and air resulting in better combustion.

Study of Time-Resolved Vortex Structure of In-Cylinder Engine Flow Fields Using Proper Orthogonal Decomposition Technique

The structure of in-cylinder flow field makes significant impacts on the processes of fuel injection, air–fuel interactions, and flame development in internal combustion engines. In this study, the implementation of time-resolved particle image velocimetry (PIV) in an optical engine is presented. Flow field PIV images at different crank angles have been taken using a high-speed double-pulsed laser and a high-speed camera with seeding particles mixed with the intake air. This study is focused on measuring the flow fields on the swirl plane at 30 mm below the injector tip under various intake air swirl ratios. A simple algorithm is developed to identify the vortex structure and to track the location and motion of vortex center at different crank angles. Proper orthogonal decomposition (POD) has been used to extract the ensemble and variation information of the vortex structure. Experimental results reveal that strong cycle-to-cycle variations exist in almost all test conditions. The vortex center is difficult to identify since multiple, but small scale, vortices exist during the early stage of the intake stroke. However, during the compression stroke when only one vortex center exists in most cycles, the motion of vortex center is found to be quite similar at different intake swirl ratios and engine speeds. This is due to the dominant driving force exerted by the piston’s upward motion on the in-cylinder air.

Effects of engine parameters on ionization current and modeling of excess air coefficient by artificial neural network

This study investigates the effects of engine speed, load, ignition timing and excess air coefficient on the ionization current and presents an artificial neural network model to predict the in-cylinder air-fuel ratio by using data of the ionization current. A secondary spark plug was used as an ionization current sensor. Experimental studies were conducted on a spark-ignition engine at variable speed, load, ignition timing, and excess air coefficient. The effects of these parameters on the ionization current were investigated individually. For modeling of the excess air coefficient, an artificial neural network model was developed with the experimental results. The network was trained with Levenberg-Marquardt and Scaled Conjugate Gradient training algorithms. Performance of the network was measured by comparing the predictions with the remaining experimental results. The excess air coefficient can be predicted with the network with a coefficient of determination of 0.99508. This study shows, the ionization current signal can be used to predict the in-cylinder excess air coefficient as a feasible alternative to the production air-fuel ratio sensors.

Effects of Scavenging System Configuration on In-Cylinder Air Flow Organization of an Opposed-Piston Two-Stroke Engine

In-cylinder air flow is very important from the point of view of mixture formation and combustion. In this direction, intake chamber structure and piston crown shape play a very crucial role for in-cylinder air pattern of opposed-piston two-stroke (OP2S) engines. This study is concerned with the three-dimensional (3D) computational fluid dynamics (CFD) analysis of in-cylinder air motion coupled with the comparison of predicted results with the zero-dimensional (0D) parametric model. Three configurations viz., a flat piston uniform scavenging chamber, a flat piston non-uniform scavenging chamber and a pit piston non-uniform scavenging chamber have been studied. 0D model analysis of in-cylinder air flow is consistent with 3D CFD simulation. It is concluded that a pit piston non-uniform scavenging chamber is the best design from the point of view of tumble ratio, turbulent kinetic energy and turbulent intensity, which play very important roles in imparting proper air motion. Meanwhile a flat piston uniform scavenging chamber can organize a higher swirl ratio and lower tumble ratio which is important to improve the scavenging process.

An experimental investigation into the starting process of free-piston engine generator

This paper presents an experimental investigation of the starting process of a prototype free piston engine generator (FPEG). Experimental test results show that during the motoring stage, the peak in-cylinder pressure and compression ratio increase in a non-linear manner and trend to reach a stable state after a number of cycles. The motoring force is suggested to be within a reasonable range. With a fixed starting force of 125N, the in-cylinder air fuel mixture was successfully ignited at the fourth cycle with a compression ratio of over 9:1. The peak in-cylinder pressure for the first combustion cycle reached over 40bar. The piston ran at high and relatively constant speed at the middle portion of the stroke. The peak piston velocity increases significantly to around 4.0m/s. Cycle-to-cycle variation of the piston movement was significant and the engine misfired frequently. During the misfire cycles, the peak piston velocity decreased to nearly 2.5m/s; and the piston dynamics were similar to the motoring process. Based on these, discussion on misfire and further stable running control, as well as the linear electric machine mode switch were presented.

Effect of piston shape on in-cylinder flows and air–fuel interaction in a direct injection spark ignition engine – A CFD analysis

DISI (Direct injection spark ignition engines) are very popular today because of their low fuel consumption and exhaust emissions due to their operation at lean stratified mixture. Their performance depends on the level of mixture stratification, which in turn depends on in-cylinder flows and air-fuel interaction at the time of fuel injection. However, these are very much affected by combustion chamber configuration, which in turn is mainly dependent upon the piston shape. In this study, a CFD (computational fluid dynamics) analysis is carried out to analyze in-cylinder air flows and air-fuel interaction created by different piston shapes viz., flat, flat-with-center-bowl, inclined and inclined-with-center-bowl pistons in a four-stroke engine at an engine speed of 1500 rev/min. Here, a start of fuel injection is considered at end of the suction stroke with a multi-hole injector operating at an injection pressure of 500 bar. Engine specifications are selected from the literature for which experimental data is available for comparison. Finally, it is found that flat-with-center-bowl piston results in about 51% higher tumble ratio and about 21% higher turbulent kinetic energy of in-cylinder flows, better mixture stratification along with 33% higher evaporation rate and 33% higher percentage of fuel evaporation as compared to those of flat piston.

PIV examination of spray-enhanced swirl flow for combustion stabilization in a spray-guided stratified-charge direct-injection spark-ignition engine

Practical implementation of spray-guided stratified-charge direct-injection spark-ignition engines can be inhibited by combustion instability, in particular the occurrence of misfire and partial burns. Performance testing in an all-metal spray-guided stratified-charge direct-injection spark-ignition engine shows that increasing the engine speed from 1000 to 2000 r/min can cause a deterioration of the combustion stability for operation without intake-generated swirl. Introducing swirl to the in-cylinder air charge motion maintains combustion stability while the speed is increased. To gain understanding how swirl reduces cycle-to-cycle variability of the flow, two-dimensional Particle Image Velocimetry (PIV) measurements were made in a horizontal swirl plane near the top of the piston bowl and in a central vertical tumble plane. Tests with and without injection were conducted at 1000 and 2000 r/min for operation both with and without swirl. The results demonstrate that the swirl creates flow patterns in each cycle that are more similar to the ensemble-averaged cycle, and with decreased variability. Furthermore, the fuel injection causes a redistribution of angular momentum resulting from spray–swirl interaction. The gas-phase swirl flow is redistributed by the spray to create a very repeatable vortex with enhanced angular momentum close to the spray centerline. This decreases the cycle-to-cycle variability of the flow patterns. Quantified changes in the stability of the flow patterns with swirl and engine speed are consistent with the combustion-instability trends.

An Investigation into In-Cylinder Tumble Flow Characteristics with Variable Valve Lift in a Gasoline Engine

In this paper, the investigation into in-cylinder tumble flow characteristics with reduced Maximum Valve Lifts (MVL) is presented. The experimental work was conducted in a modified four-valve Spark-Ignition (SI) test engine, with optical accesses for measuring in-cylinder air motion in the vertical direction. Three different MVL of 6.8 mm, 4.0 mm and 1.7 mm were tested and Particle Image Velocimetry (PIV) was employed for those measurements. Measurement results were analysed by examining the tumble flow field, the tumble ratio variation and the fluctuating kinetic energy distribution. Meanwhile, a numerical analysis method for detecting the vortex centre was developed. From results of the vortex centre distribution, the cyclic variation of the in-cylinder flow was explored. The phase-averaged flow fields show that higher MVLs could produce stronger vertical flows which turn more toward to the piston top and finally are possible to form big scale tumble flow structure. Although lower MVLs create a higher tumble ratio when the piston is close to the Bottom Dead Centre (BDC), higher MVLs substantially produce higher tumble ratios when the piston is moving close to the Top Dead Centre (TDC). In terms of kinetic energy, lower MVLs result in higher values including higher total kinetic energy and higher fluctuating energy. Finally, the vortex centres results demonstrate lower MVLs could enhance cycle-to-cycle variation due to the weakened tumble vortex.

Analysis of Diesel Engine In-Cylinder Air-Fuel Mixing with Homogeneity Factor: Combined Effects of Pilot Injection Strategies and Air Motion

With a view to understanding the air-fuel mixing behavior and the effects of the mixture quality on the emissions formation and engine performance, a new quantitative factor of the in-cylinder air-fuel homogeneity named Homogeneity Factor (HF) has been developed. Its characteristics under various injection conditions and air swirl motions within the cylinder have been investigated with CFD simulation. The results have shown that air-fuel homogeneity is essentially affected by the spatial and temporal fuel distribution within the combustion chamber. Higher injection pressure, longer dwell time and increased pilot fuel quantities can contribute to better mixing quality resulting in increased HF and optimum engine performance with low fuel consumption and soot emissions. With regard to the in-cylinder air motion, increasing swirl ratio enhances the air-fuel mixing quality which has been reflected in the variation of the HF. As a result, increased in-cylinder pressure and temperature caused by the optimized air-fuel mixing improved the combustion efficiency.

Optical investigation of fuel and in-cylinder air-swirl effects in a high-speed direct-injection engine

The primary aim of this study is to investigate current issues of combustion in high-speed direct-injection diesel engines in detail by optical diagnostics. Both fuel and engine design are considered. Recently, measurements of engine-out emissions demonstrated that approximately soot-free combustion can be achieved using a newly designed two-component fuel named BLT. It was composed of 70% butyl levulinate and 30% n-tetradecane (by volume). In this work, the underlying mechanism is clarified by in-cylinder visualization of OH* radicals and soot. In particular, it turns out that in-cylinder soot formation is avoided almost completely, that is, the soot oxidation process is much less important. This is basically achieved by both the oxygen content (about 21%) and the low cetane number (approximately 33) of BLT. The latter leads to enhanced pre-mixing of fuel and air. Consequently, soot formation can be greatly reduced because it depends on the air–fuel ratio of the mixture shortly before high-temperature combustion. The influence of in-cylinder air swirl on combustion and soot formation is also studied for both BLT and conventional diesel fuel, respectively, using the same optical diagnostic. The measurements show that the combustion zone strongly depends on the local gas-flow velocity for diesel fuel. Soot formation decreases with increasing swirl because of enhanced air entrainment and pre-mixing of fuel and air. In addition, the results indicate that soot oxidation is improved under high-swirl conditions for diesel fuel. In contrast, the influence of swirl on the combustion of BLT is overall found to be weak, suggesting that swirl could be reduced in future high-speed direct-injection engines for BLT-like fuels.

Effects of advanced injection strategies on the in-cylinder air–fuel homogeneity of diesel engines

The air–fuel mixing quality in the combustion chamber of a diesel engine is very critical for controlling the ignition and the combustion quality of direct-injection diesel engines. With a view to understanding the air–fuel mixing behaviour and the effect of the mixture quality on the emissions formation, an innovative approach with a new quantitative factor of the in-cylinder air–fuel homogeneity, called the homogeneity factor, was used, and its characteristics under various injection conditions were analysed with computational fluid dynamics simulations. By investigating the effect of advanced injection strategies on the homogeneity of the mixture and the emissions production, the study suggested that the homogeneity factor is greatly affected by the pulse number of injections, the injection timing and the dwell angle between two injections. The more advanced the injection taking place in the cylinder, the earlier the air–fuel mixing quality reaches a high level. Although the homogeneity factor is not sufficiently precise by itself to reflect the emissions formation, the results demonstrated that most often, the higher the homogeneity available in the cylinder, the more nitrogen oxides and the less soot were formed.

Cycle-to-cycle variation analysis of early flame propagation in engine cylinder using proper orthogonal decomposition

Experimental investigations on the cycle-to-cycle variations of early flame propagation were conducted at two intake air swirl ratio of 0.55 and 5.68 in a single-cylinder spark-ignition direct-injection (SIDI) optical engine. Both the crank-angle resolved flame images through the quartz insert in the piston and the in-cylinder pressure were simultaneously recorded for 250 consecutive cycles. An algorithm based on the cross-correlation of flame pattern was implemented to compute the two-dimensional velocity fields representing an early flame propagation. Afterwards, the proper orthogonal decomposition (POD) was performed to access the cycle-to-cycle variations of flame propagation. During early flame formation, the uncertainty of velocity was evaluated to be less than 5%. The velocity fields of early flame propagation were significantly affected by in-cylinder air flow. Increasing the swirl ratio from 0.55 to 5.68 augmented the average early flame propagation speed from 2.1m/s to 3.2m/s, and the COV of flame speed was reduced from 49.7% to 25.1%. Good correlations were identified between early flame speed and the pressure-derived results. Similar magnitude of reduction in COV (coefficient of variation) of IMEP (indicated mean efficient pressure) & PP was also found. The coefficients of POD mode 1 were found to represent the flame speed, and the remaining higher POD modes were related to the fluctuation in kinetic energy. The POD coefficients showed good correlations with the pressure-derived results such as CA05 (5% of total heat release) & PP (peak pressure). The weak spiral flow pattern, observed within the flame, was only found in higher POD modes. In summary, using the coefficients and modes of POD, the average and fluctuating parts of early flame propagation can be resolved, thereby providing more quantitative information of the cycle-to-cycle variation during the early combustion process in an engine cylinder.

Proper orthogonal decomposition analysis of fuel spray structure variation in a spark-ignition direct-injection optical engine

For spark-ignition direct-injection (SIDI) engines in which fuel is injected directly in the cylinder, large amount of in-cylinder mixture variation on a cyclic basis could adversely influence the combustion quality and lead to more fuel consumption and excessive engine emissions. In this study, multiple cycles of intake air flow fields and their effects on fuel spray structure were investigated experimentally in an optical SIDI engine. Proper orthogonal decomposition (POD) was utilized to identify and quantify the cyclic variations of intake air motions and spray the pattern in the cylinder. Results show that the pattern of POD mode 1 resembles the ensemble-averaged structure of intake air velocity field. Other higher POD modes are useful to identify the fluctuations of the flow. The cycle-to-cycle difference of in-cylinder air flow motion also influences the variations of spray structure on a cyclic basis, which can be unambiguously quantified by analyzing the POD modes 1 and 2 of the spray pattern. Whereas the first mode exhibits the variation for the dominant portion of spray structure, the second mode captures the subtle differences in the positions of discrete fuel spray plumes under the influence of intake air. Overall, POD can be useful in identifying and quantifying the cyclic variations of the intake air motion and spray structure in the cylinder of running engine conditions.

Optimizations of Vane Height of Guide Vane Swirl and Tumble Device to Improve in Cylinder Airflow Characteristics of a Diesel Engine Running with Vegetable Oil

Generally, compression ignition engine operating on neat vegetable oil and its blend with diesel fuel experience a reduction of engine performance and increase in exhaust emissions due to higher viscosity and lower volatility of vegetable oil than diesel fuel. Vegetable oil is less prone to evaporate, diffuse and mix with the in-cylinder air which eventually reduces the combustion efficiency and produces more emissions of CO and unburned HC. Therefore, this research investigated the potential of guide vane swirl and tumble device (GVSTD) to guide the air entrance to create more organized turbulence inside the fuel injected region to enhance the mixing process of air and vegetable oil. In order to do so, a base model of 3D computational fluid dynamic of internal combustion engine simulation was developed, verified and then simulations were carried with different GVSTD models. The results of turbulent kinetic energy, velocity, vorticity and swirling strength were compared to determine the optimum vane height. This research found that the 2 mm vane height was the optimum vane height with 35° twist angle, four vanes being arranged perpendicularly to each other and 30 mm vane length. Other different heights of vanes also showed improvement but 2 mm height showed the highest number of improvements. This could be due to the airflow pattern in bowl-inpiston head shape was amplified by the airflow pattern produced by the guide vane of 2 mm vane height. The extra turbulence, swirl, vorticity and velocity in the fuel injected region created by the 2 mm height vane is expected to enhance the mixing of vegetable oils with air to improve combustion and reduce CO and unburned HC emissions.

Guide Vane Swirl and Tumble Device to Improve in-cylinder Air Flow of CI Engine Using Vegetable Oil

A guide vane swirl and tumble device (GVSTD) can be used in compression ignition (CI) engines running on vegetable oils to generate better in-cylinder air flow characteristics to improve combustion efficiency. In this paper, IC engine simulations were performed to determine the effect of GVSTD on the air flow using 3D computational fluid dynamics (CFD) software. The effects of various vane heights by means of parametric optimization were investigated. The results of average in-cylinder pressure, turbulent kinetic energy (TKE) and velocity were analyzed before the optimum vane height to the pre-set values of vane angle, number and length were decided. Interestingly, the highest vane height failed to improve all the analyzed parameters. At a GVSTD vane height of 0.2 times the intake runner radius, the average in-cylinder pressure, TKE and velocity were found better than with other settings.

English

This paper investigates the in-cylinder air flow of a compression ignition (CI) engine modified by a guide vane swirl and tumble device (GVSTD) where the number of GVSTD vanes was varied to optimize its dimension to improve the CI engine performance using higher viscous fuel (HVF). Hence, eleven 3D CI engine models were developed; a base model and 10 GVSTD models, via SolidWorks. Computational fluid dynamics (CFD) were performed by utilizing ANSYS-CFX and simulated under motored conditions for two continuous complete cycles. The results are presented of the simulation of in-cylinder pressure, turbulence kinetic energy (TKE) and velocity during the fuel injection period until expansion. The recorded increments from six vanes of GVSTD were about 1.3%, 0.2% and 22% of the above results. Hence, this paper concludes that GVSTD has the potential to improve CI engine performance using HVF.

Transient Air-to-Fuel Ratio Control of an Spark Ignited Engine Using Linear Quadratic Tracking

Modern spark ignited (SI) internal combustion engines maintain their air-to-fuel ratio (AFR) at a desired level to maximize the three-way catalyst conversion efficiency and durability. However, maintaining the engine AFR during its transient operation is quite challenging due to rapid changes of driver demand or engine throttle. Conventional transient AFR control is based upon the inverse dynamics of the engine fueling dynamics and the measured mass air flow (MAF) rate to obtain the desired AFR of the gas mixture trapped in the cylinder. This paper develops a linear quadratic (LQ) tracking controller to regulate the transient AFR based upon a control-oriented model of the engine port fuel injection (PFI) wall wetting dynamics and the air intake dynamics from the measured airflow to the manifold pressure. The LQ tracking controller is designed to optimally track the desired AFR by minimizing the error between the trapped in-cylinder air mass and the product of the desired AFR and fuel mass over a given time interval. The performance of the optimal LQ tracking controller was compared with the conventional transient fueling control based on the inverse fueling dynamics through simulations and showed improvement over the baseline conventional inverse fueling dynamics controller. To validate the control strategy on an actual engine, a 0.4 l single cylinder direct-injection (DI) engine was used. The PFI wall wetting dynamics were simulated in the engine controller after the DI injector control signal. Engine load transition tests for the simulated PFI case were conducted on an engine dynamometer, and the results showed improvement over the baseline transient fueling controller based on the inverse fueling dynamics.

Analysis of In-Cylinder Air Motion in a DI Diesel Engine with Four Different Piston Bowl Configuration - A CFD and PIV Comparison

Analysis of In-Cylinder Air Motion in a DI Diesel Engine with Four Different Piston Bowl Configuration - A CFD and PIV Comparison

The Influence of In-Cylinder Flows on Emissions and Heat Transfer from Methane-Diesel Dual Fuel Combustion

Currently there is a large interest in alternative transport fuels. There are two underlying reasons for this interest: the desire to decrease the environmental impact of transports and the need to compensate for the declining availability of petroleum. In the light of both these factors, the CNG-diesel dual fuelengine is an attractive concept. The primary fuel of the dual fuel engine is methane, which can be derived both from renewables and from fossil sources. Methane from organic waste, commonly referred to as biomethane, can provide a reduction in greenhouse gases unmatched by any other fuel. Furthermore, fossil methane, natural gas, is one of the most abundant fossil fuels.Thedual fuelengine is, from a combustion point of view, a hybridof the diesel and theOtto-engineand it shares characteristics with both.From a market standpoint, the dual fuel technology is highly desirable; however, from a technical point of view it has proven difficult to realize. The aim of this project was to identify limitations to engine operation, investigate these challenges, and ,as much as possible, suggest remedies. Investigations have been made into emissions formation, nozzle-hole coking, impact of varying in-cylinder air motion, behavior and root causes of pre-ignitions, and the potential of advanced injection strategies and unconventional combustion modes. The findings from each of these investigations have been summarized, and recommendations for the development of a Euro 6 compliant dual fuel engine have been formulated. Two key challenges must be researched further for this development to succeed: an aftertreatment system which allows for low exhaust temperatures must be available, and the root cause of pre-ignitions must be found and eliminated.

Optimize Vane Length to Improve In-Cylinder Air Characteristic of CI Engine Using Higher Viscous Fuel

Environmental issues and the depletion of worldwide crude oil sources have developed the requirement for an alternative fuel to power internal combustion engines. Vegetable oil, waste cooking oil and biodiesel are all renewable, environmentally sustainable and compatible with current Compression Ignition (CI) engines with little to no engine modification necessary. These fuels however have a higher viscosity than conventional petro-diesel and may be referred to as Higher Viscous Fuels (HVF). HVF have reduced in-cylinder combustion efficiency when compared with petro-diesel which reduces the engine performance in terms of output power, torque and fuel efficiency. A possible solution to the reduced efficiency is through the use of a Guide Vane Swirl and Tumble Device (GVSTD). This device when installed in front of the air intake manifold may produce improved air flow characteristics. This improves the efficiency of the evaporation processes and air-fuel mixing and therefore improves overall combustion efficiency. The effect of GVSTDs on in-cylinder air flow was studied using 3D Internal Combustion (IC) engine simulation under motored engine conditions. This was done using ANSYS-CFX. The base model engine was adapted from the Hino W04D model CI engine. The model throughout all simulations was run at a constant speed of 1500 rpm. There are four parameters to consider for GVSTD models; vane length, vane height, vane angle and the number of vanes. For the purpose of this study, the vane height, vane angle and the number of vanes were maintained as constants leaving the vane length as the variable parameter. 11 GVSTD models were simulated each varying from 1.5 to 4.5 times the radius of the intake runner (R) in 0.3R increments. To analyze the air-flow characteristics, the maximum in-cylinder pressure, Turbulence Kinetic Energy (TKE) and velocity were measured. It was found that for the constant values for vane height, vane angle and the number of vanes of 0.2R, 35° twist angle and 4 perpendicularly-arranged respectively, the in-cylinder pressure, TKE and velocity were optimum for the vane lengths of 3.6 to 3.9 times R.