Expansion Stroke Research Articles

Effects of lubricant shear thinning on the mixed lubrication of piston skirt-liner system

A theoretical analysis is presented for the mixed lubrication of the piston skirt-liner system. The model is developed to consider the shear thinning effect of multigrade lubricant. The friction characteristics of the piston skirt-liner system for both monograde and multigrade lubricants are investigated. It is found that a decrease in the lubricant viscosity is effective in reducing the friction loss. However, the boundary friction at the expansion stroke will increase with low lubricant viscosity. Results in this study show a significant lubricant shear thinning effect on the piston skirt-liner system.

Experimental investigation of hydraulic effects of two-stage fuel injection on fuel-injection systems and diesel combustion in a high-speed optical common-rail diesel engine

In order to meet the ever more stringent emission standards, significant efforts have been devoted to the research and development of internal combustion engines. The requirements for more efficient and responsive diesel engines have led to the introduction and implementation of multiple injection strategies. However, the effects of such injection modes on the hydraulic systems, such as the high-pressure pipes and fuel injectors, must be thoroughly examined and compensated for since the combustion and the formation of pollutants in direct-injection engines are directly influenced by the spatial and temporal distribution of the injected fuel within the combustion chamber. This study investigated the hydraulic effects of two-stage fuel injection on diesel combustion and emissions. The fuel-injection system was characterised for all the tested strategies through the measurement of the fuel-injection rate and quantity. In particular, the interaction between the two injection events was identified. The effects of two-stage injection, dwell angle and the interactions between two consecutive injection events on the combustion process and the emissions were investigated in a high-speed direct-injection single-cylinder optical diesel engine using heat-release analysis and high-speed fuel spray and combustion visualisation techniques. The results indicated that the two-stage injection strategy has the potential for simultaneous reduction of nitrogen oxide, soot and unburned hydrocarbon emissions. The results suggested that an optimum fuel quantity in the first injection exists, 0–30%, with which simultaneous reduction of nitrogen oxide, soot and unburned hydrocarbon emissions can be achieved with the added benefits of improved engine performance, fuel economy and combustion noise. However, higher soot emissions were produced, mainly due to the interaction between the two consecutive fuel-injection events whereby the fuel sprays during the second injection were injected into burning regions, as well as reduced soot oxidation due to the continuation of the combustion into the expansion stroke.

High-speed micro particle image velocimetry studies of boundary-layer flows in a direct-injection engine

Mass and energy exchange processes near the in-cylinder walls have become increasingly important for internal combustion engine research and development. Heat-transfer and fuel-deposition processes are not well enough understood to fully predict their magnitude and temporal and spatial variation. To a large extent, improvements in modeling are limited because of a lack of experimental guidance on the dynamics of boundary-layer flows in engines. High-speed particle image velocimetry and micro particle image velocimetry were used to study the boundary-layer flow field at the cylinder head of a motored internal combustion engine for three different engine speeds (400, 800 and 1100 r/min). Velocity measurements were taken throughout the compression stroke and the beginning of the expansion stroke, and comparisons to the frequently used law-of-the-wall were made. The low-resolution particle image velocimetry images showed that the average bulk flow maintained a tumble flow throughout the compression and expansion strokes and velocities scaled with engine speed. Adequate spatial resolution of the boundary-layer flow required the use of high-resolution (micro particle image velocimetry) measurements which showed that the log-law does not accurately describe the experimental boundary-layer structure in the outer layer ([Formula: see text]). Using the log-law, the velocity for earlier crank angles (180–260 crank angle degrees) was over predicted while the velocity for later crank angles (300–330 crank angle degrees) was under predicted, as engine speed increased. However, the experimental velocity profiles near the wall ([Formula: see text]) matched the description of the viscous sublayer ([Formula: see text]). Furthermore, it was observed that the thickness of the viscous sublayer decreased as the engine speed increased. The viscous sublayer could not be adequately resolved at 1100 r/min because of the limitations in adequate seeding density near the surface and the resulting loss of data points closest to the wall. The capability of high-speed particle image velocimetry measurements is demonstrated by the ability to identify and track vortical structures that move through the outer and buffer layers. Future work must address the evolution of such flow structures, along with measurements of temperature, to enable development and validation of boundary-layer models that are not restricted by the assumptions necessary for the law-of-the-wall such as steady bulk flow conditions and properties.

Measurement of in-cylinder soot particles and their distribution in an optical HSDI diesel engine using time resolved laser induced incandescence (TR-LII)

Soot particles generated during combustion process in a single cylinder optical diesel engine were measured using time-resolved laser induced incandescence technique (TR-LII). Experimentally measured LII data were fitted with theoretically simulated LII data to determine the count median particle diameter and the geometric width of the particle size distribution. TR-LII signals were acquired simultaneously at two different wavelengths for crank angles in the range from 48.4° to 111.4° after top dead centre (aTDC) and for various engine operating conditions. Particle size was found to be dependent on the engine load but no significant change in particle sizes were observed for different fuel injection timings. The average size of the primary particles measured over different crank angles were larger at higher engine loads compared to lower engine loads. A general trend of the soot particle diameter decreasing with crank angle was observed due to oxidation, but towards the end of the expansion stroke a marginal increase in size was noted. For all operating conditions the width of the particle size distribution was found to decrease with crank angle until 61.4°aTDC, and thereafter it increases to reach a well defined size distribution for a given fuel injection quantity despite the differences in the injection timing. The soot particles are randomly transported by the complex fluid motion present within the combustion chamber leading to strong cycle to cycle fluctuations of the measured time resolved LII data. The in-cylinder soot volume fraction derived from TR-LII data revealed that for different fuel injection timings, a relatively higher amount of soot was produced for shorter ignition delay compared to larger ignition delays.

A Study of the Effects of Biofuel Use on Piston Lubrication During Fuel Post Injection in a Direct Injection Diesel Engine

The reduction of both exhaust gases and carbon dioxide emissions is necessary to meet future emissions regulations for diesel engines. Exhaust after-treatment devices are gradually being applied to diesel engines to reduce exhaust gases. Diesel particulate filters (DPF), an after-treatment device for diesel engines, in some cases require fuel post injection for regeneration. Post injection is usually conducted at the midpoint of the expansion stroke, and therefore causes fuel adhesion to the cylinder wall. However, using biofuels in a diesel engine is an effective way of reducing carbon dioxide emissions. It is well known that biofuels are chemically unstable, but the effects of biofuels on piston lubrication condition have not been thoroughly studied. In this study, piston lubrication condition during post injection in a single cylinder DI diesel engine using biofuel was investigated. Piston and ring friction forces were measured under engine operating conditions by means of a floating liner device to investigate the lubrication condition of the piston and rings. Both light fuel oil and biofuel were used in the measurements, with rapeseed methyl ester (RME) being used as the biofuel. Lubricating oil on the cylinder wall was also sampled under engine operating conditions, and the effect of post injection on fuel adhesion to the cylinder wall was analyzed. It was found that the effect of post injection on fuel adhesion to the cylinder wall was remarkable around the top dead center (TDC), and the fuel dilution rate reached approximately 90%. The results of the measurement of the piston friction forces showed that post injection caused an increase in the friction forces at the compression TDC (CTDC) in the cases of both RME and light fuel oil, and the friction forces at CTDC increased according to the delay of the post injection timing. The increase in the piston friction forces was moderate in the case of RME. It seems that the higher viscosity and the oiliness of RME suppressed the increase in piston friction forces at TDC. The following effects were found in this study. Fuel post injection caused fuel adhesion to the cylinder wall. Such phenomena affected the lubrication condition of the piston. In the case of RME, the increase in the piston friction forces caused by post injection was smaller than that of light fuel oil, but the effects on piston lubrication condition in the case of using other biofuels needs to be investigated.

Influence of Fuel Injection on Gasoline Engine Performance

Because of the most common method of preparing the fuel-air mixture for gasoline-fueled engines is port fuel injection (PFI). For reducing the wall-film entering the cylinder in liquid phase, the phenomena of wall-film entering the cylinder in liquid phase should be at minimum lever or be avoided. So the first thing for learning the wall-film is to detect the way of the wall-film entering the cylinder. Therefore, the way of the wall-film enter the cylinder in liquid phase is detected by changing the temperature of the wall-film location and time for wall-film evaporated. Then the way is validated by experiment test bed and it is improved that the way is feasible. At the end the influence of injection timing and fuel ratio on engine performance is studied based on the test bed.The results show that regardless of the expansion stroke or the intake stroke fuel injection the injection timing delay will decrese the engine power and make emission deterioration meanwhile the twice fuel injection can improve the fuel film evaporation resulting of high-speed airflow of intake charge. DOI: http://dx.doi.org/10.11591/telkomnika.v11i4.2398

Researching on Valve System of Hydraulic Electromagnetic Energy-Regenerative Shock Absorber

Hydraulic electromagnetic energy-regenerative shock absorber is a new kind of shock absorbers, who can perform the function of a standard shock while acting as an additional source of power. One of the core components of this new shock absorber is the valve system. And its function is to rectify the direction of the oil flow. Then the oil can flow through the hydraulic motor from one port only no matter in expansion stroke or compression stroke. The research focused on the compactness, sensitivity and energy recovery rate of two different valve systems. And the results showed that the valve system composed of check valves better matched the hydraulic electromagnetic energy-regenerative shock absorber.

Convective Heat Transfer in a Pneumatic Hybrid Engine

Several previous studies have proven that pneumatic hybridization of an internal combustion engine is a technically viable and cost-efficient alternative to electric hybridization. Because the heat transfer process remains a first order factor while the engine operates in a motored or pneumatic mode without combustion, an accurate instantaneous heat transfer model is required in order to predict the in-cylinder pressure. This study shows that the original Woschni model is not suitable for describing the shape of the measured instantaneous heat flux versus crank angle while the engine operates in a motored pneumatic mode, because of the extinction of tumble motion near Top Dead Center (TDC). A modified form of the Woschni model is therefore proposed here that better describes the instantaneous heat flux during compression and expansion strokes, applicable to pneumatic and motored with fuel cut-off modes. First, the new constant parameter model is identified from experimental measurements performed in various motored mode conditions. Next, the pneumatic supercharged mode without combustion (ignition not performed) is investigated with the new model using the same identification values as for the motored mode. This study shows that the modified model remains fully applicable to the supercharged mode, despite of a certainly modified in-cylinder aerodynamic structure created by the opening of the charging valve under a high pressure ratio.

Experimental study of syngas combustion at engine-like conditions in a rapid compression machine

As the world energy demand and environmental concern continue to grow, syngas is expected to play an important role in future energy production. It represents a viable energy source, particularly for stationary power generation, since it allows for a wide flexibility in fossil fuel sources, and since most of the harmful contaminants and pollutants can be removed in the post-gasification process prior to combustion. In this work, two typical mixtures of H 2, CO, CH 4, CO 2 and N 2 have been considered as representative of the producer gas coming from wood gasification, and its turbulent combustion at engine-like conditions is made in a rapid compression machine in order to improve current knowledge and provide reference data for modeling and simulation of internal combustion engines. Methane as main constituent of the natural gas is used as reference fuel for comparison reasons. Single compression and compression- expansion events were performed as well direct light visualizations from chemiluminescence emission. There is an opposite behavior of the in-cylinder pressure between single compression and compression–expansion strokes. For single compression, peak pressure decreases as the ignition delay increases. In opposite, for compression–expansion the peak pressure increases as the ignition delay increases. This opposite behavior has to do with the combustion duration under constant volume conditions. Conclusion can be drawn that higher pressures are obtained with methane–air mixture in comparison to both typical syngas compositions. These results could be endorsed to the heat of reaction of the fuels, air to fuel ratio and burning velocity. Another major finding is that syngas typical compositions are characterized by high ignition timings due to its low burning velocities. This could compromise the use of typical syngas compositions on high rotation speed engines.

A cold-start method and analysis for internal combustion engines particularly using a renewable fuel

A new cold-start approach for internal combustion engines is described, which may be particularly suitable for an engine using an alternative fuel, such as ethanol or methanol. One of the cylinders in the engine may be equipped with a holding chamber in the cylinder head for the cold-start purpose. The holding chamber may be opened or closed by a holding chamber valve to establish or block the fluid flow between the holding chamber and the cylinder space. The cold-start procedure includes an intake stroke and a compression stroke, an expansion stroke that conserves the energy content of the earlier compressed charge without returning the compression work to the piston, and a subsequent recompression stroke to compress the charge to a much higher temperature. A thermodynamic analysis on the cold-start process of a homogeneous charge internal combustion engine is undertaken, which includes the effect of fuel vaporization on the temperature change of the charge during the first compression stroke. It is found that the charge could be compressed effectively to a sufficiently higher temperature for ignition with pure ethanol as fuel. Copyright © 2010 John Wiley & Sons, Ltd.

Wear Mechanisms Approach to Ni-P Electroless Plating Applied to Hardening Engine Cylinder

For practical operation conditions of engine cylinder, piston speed and lateral pressure to cylinder wall are determined as experimental factors. According to load and speed on 1mm~8mm below top dead center of cylinder in expansion stroke, the ranges of experimental parameters are chosen. Based on the quadratic regression rotation combination method, wear resistance experiment of hardening material is designed. The wear mathematic models of Ni-P electroless plating is established, and three-dimensional curved surfaces for load-speed-wearing value are drawn. The results show that the Ni-P electroless plating can increase relative wear resistance of cylinder by 5 times. By analysis of wear mechanisms of hardening material and wear resistance, the material is perfect for hardening engine cylinder wall.

The realization and analysis of a new thermodynamic cycle for internal combustion engine

This paper presents description and thermodynamic analysis of a new thermodynamic cycle. Realization of this new cycle is possible to achieve with valveless internal combustion engine with more complete expansion. The main purpose of this new IC engine is to increase engines’ thermal efficiency. The engine was designed so that the thermodynamic changes of the working fluid are different than in conventional engines. Specific differences are reflected in a more complete expansion of the working fluid (the expansion stroke is larger than compression stroke), valveless gas flowing and complete discharge of residual combustion products from the combustion chamber. In this concept, the movement of the piston is different than in conventional piston mechanisms. The results obtained herein include the efficiency characteristics of irreversible reciprocating new engine cycle which is very similar to Miller cycle. The results show that with this thermodynamic cycle engine has higher efficiency than with the standard Otto cycle. In this article, the patent application material under number 2008/607 at the Intellectual Property Office of the Republic of Serbia was used.

Quasi-Dimensional Modeling of a CNG Fueled HCCI Engine Combustion Using Detailed Chemical Kinetic

In this study, an in-house quasi dimensional code has been developed which simulates the intake, compression, combustion, expansion and exhaust strokes of a homogeneous charge compression ignition (HCCI) engine. The compressed natural gas (CNG) has been used as fuel. A detailed chemical kineticscheme constituting of 310 and 1701 elementary equations developed by [Bakhshan and al.] has been applied for combustion modeling andheat release calculations. The zero-dimensional k-e turbulence model has been used for calculation of heat transfer. The output results are the performance and pollutants emission and combustion characteristics in HCCI engines. Parametric studies have been conducted to discussing the effects of various parameters on performance and pollutants emission of these engines.

A variable volume approach of tabulated detailed chemistry and its applications to multidimensional engine simulations

In the context of engine development for low fuel consumption and low emissions, combustion modeling is a challenging subject as the requirements for lower pollutant emissions mean that accurate temporal and spatial predictions of the heat release and species concentrations are needed. Among the various approaches developed recently to account for these processes in realistic configurations, tabulated techniques appear to be a promising approach. A good compromise can be obtained between the accuracy brought by detailed chemistry at limited computational cost. Tabulation approaches were first developed and successfully applied to stationary combustors at constant pressure. However, these approaches are severely limited for internal combustion engine applications: indeed, they are not capable of accounting for the enthalpy or energy loss due to the pressure work in the expansion stroke. To overcome this limitation a new Variable Volume Tabulated Homogeneous Chemistry (VVTHC) approach is proposed in this study. It provides the evolution of major species and radicals from the onset of auto-ignition up to the end of the expansion stroke for compression ignited and spark ignited engine applications. It is first validated for homogeneous engine cases where it compares very well to complex chemistry simulations. Implemented in a piston engine combustion model, it also succeeds in matching the burned gases volume variation behind a propagating flame at constant pressure and in reproducing the subsequent composition evolution. In these conditions, the new approach gives results similar to those obtained with classical constant pressure tabulations. Finally, a feasibility calculation of a realistic stratified Diesel engine configuration is presented. On these cases, a constant volume tabulation approach is shown to compare well with VVTHC and the experiment on the evolution of pressure but not on that of species mass fractions. This comparison demonstrates the interest of the VVTHC approach for piston engine applications.

Diesel soot oxidation during the late combustion phase

The diesel soot was extracted from the chamber of a running diesel engine using a total cylinder sampling system. A structural description and size distribution of the soot spherules were performed by means of high-resolution transmission electron microscopy (HRTEM). HRTEM image analysis was carried out to achieve semi-quantitative information about the soot organization. Different nanostructures were found in dependence upon the engine test conditions. A better organization of the graphitic layers occurred for the in-cylinder soot as the expansion stroke developed. The oxygen concentrations at sampling angles and the cylinder pressure were measured. The oxidation rates of the in-cylinder soot during the late combustion phase were calculated according to the differences of spherules size distributions between two consecutive sampling angles. The soot reactivity in dependence on the nanostructure was shown after deducting the effect of oxygen concentration and temperature. The increase of resistance toward oxidation was associated to the increase of the structural order for the in-cylinder soot. The results are a useful database for testing the structure–property relationship between the nanostructure and the reactivity of the in-cylinder diesel soot.

Modified one-step reaction equation for modeling the oxidation of unburned hydrocarbons in engine conditions

The oxidation of unburned hydrocarbons from piston crevices was modeled using a modified one-step reaction equation. This new one-step oxidation model was developed by modifying the Arrhenius reaction rate coefficients of the conventional one-step reaction equation. The predictions of the new one-step oxidation model agree well with the results of the detailed chemical reaction mechanism in terms of the 90% oxidation time of the fuel. The effects of pressure and intermediate species in the burnt gas on the oxidation rate were also investigated and included as additional multiplying factors in the modification of the equation. To simulate the oxidation process of unburned hydrocarbons from a piston crevice, a two-dimensional computational mesh, based on the conventional engine geometry, was constructed with a fine mesh density at the regions of the piston crevice and cylinder wall. The number of cell layers in the cylinder was controlled according to the piston motion to model the out-flow of unburned hydrocarbons from the piston crevice during the expansion stroke. The effects of engine operational conditions on the oxidation rate were examined at several engine speeds and load conditions, and the sensitivity of the oxidation rate to the piston crevice volume was also evaluated. Finally, the new one-step oxidation model was applied to a three-dimensional computational mesh that modeled the three-dimensional engine geometry and piston-valve motions to simulate the oxidation of unburned hydrocarbons in a real engine condition.

Flow and Heat Transfer during an Expansion Stroke in a Composite Fluid/Porous System

The purpose of this study is to analyze the fluid flow and heat transfer in a pipe partially filled with porous media and provided with a flat piston during an expansion stroke. In addition to the Navier-Stokes equation for the fluid region, Brinkman-Forchheimer-Lapwood-extended Darcy’s model is introduced into the numerical solver to simulate flow and heat transfer in the porous insert. The heat transfer in porous media is studied by using the assumption of local thermal equilibrium. The discretization procedure is based on Control-Volum e-based Finite Element Method. The coupled pressure-velocity equations are solved using the SIMPLER algorithm. This investigation concerns the hydrodynamic characteristics, using the Reynolds numbers and the porosity effects, and the heat transfer characteristics using the heat capacity and the thermal conductivity ratios effects.

Liquid penetration length of heptamethylnonane and trimethylpentane under unsteady in-cylinder conditions

While strategies employing early or late direct-injection of fuel can improve emissions, they also can lead to impingement of liquid-phase fuel on the piston and/or cylinder wall due to low in-cylinder temperatures and densities during the injection event. Previous work has shown that liquid-phase fuel films formed in this way can lead to pronounced degradations in efficiency and emissions. To avoid these problems, a quantitative understanding of fuel-property effects on the liquid penetration length is needed, and this understanding must include conditions where in-cylinder thermodynamic conditions and the injection rate vary with time. This work reports liquid penetration lengths measured in an optical engine under such time-varying conditions. Diagnostics included laser light scattering for measurement of the liquid length and conventional pressure-data acquisition for heat-release analysis. Unsteady liquid penetration was characterized for different injection timings, injection pressures, intake-manifold pressures, and fuel volatilities to gain an understanding of the relative importance of these factors. Fuel volatility was studied by using two fuels, 2,2,4,4,6,8,8-heptamethylnonane (HMN) and 2,2,4-trimethylpentane (TMP), which have very different volatility characteristics. Measured liquid lengths changed as in-cylinder conditions changed, with increasing temperature and density during the compression stroke causing a decrease in liquid length, and decreasing temperature and density during the expansion stroke causing an increase in liquid length. Intake-manifold pressure and fuel volatility were found to be primary factors governing liquid length. Heat loss from the charge gas to the engine and local charge cooling due to fuel vaporization were found to have a secondary influence on liquid length. Injection pressure was found to have little effect.

Determination of TDC in internal combustion engines by a newly developed thermodynamic approach

Abstract In-cylinder pressure analysis is nowadays an indispensable tool in internal combustion engine research & development. It allows the measure of some important performance related parameters, such as indicated mean effective pressure (IMEP), mean friction pressure, indicated fuel consumption, heat release rate, mass fraction burned, etc. Moreover, future automotive engine will probably be equipped with in-cylinder pressure sensors for continuous combustion monitoring and control, in order to fulfil the more and more strict emission limits. For these reasons, in-cylinder pressure analysis must be carried out with maximum accuracy, in order to minimize the effects of its characteristic measurement errors. The exact determination of crank position when the piston is at top dead centre (TDC) is of vital importance, since a 1° degrees error can cause up to a 10% evaluation error on IMEP and 25% error on the heat released by the combustion: the position of the crank shaft (and hence the volume inside the cylinder) should be known with the precision of at least 0.1 crank angle degrees, which is not an easy task, even if the engine dimensions are well known: it corresponds to a piston movement in the order of one tenth of micron, which is very difficult to estimate. A good determination of the TDC position can be pursued by means of a dedicated capacitive TDC sensor, which allows a dynamic measurement (i.e. while engine is running) within the required 0.1° precision [1] , [2] . Such a sensor has a substantial cost and its use is not really fast, since it must be fitted in the spark plug or injector hole of the cylinder. A different approach can be followed using a thermodynamic method, whose input is in-cylinder pressure sampled during the compression and expansion strokes: some of these methods, more or less valid, can be found in literature [3] , [4] , [5] , [6] , [7] , [8] . This paper will discuss a new thermodynamic approach to the problem of the right determination of the TDC position. The base theory of the method proposed is presented in the first part, while the second part deals with the assessment of the method and its robustness to the most common in-cylinder pressure measurement errors.

Investigation of boundary layers in internal combustion engines using a hybrid algorithm of high speed micro-PIV and PTV

Heat transfer properties vary locally and temporally in internal combustion engines due to variations in the boundary layer flow. In order to characterize the dynamics in the boundary layer, crank-angle resolved high-speed micro particle image velocimetry (μPIV) and particle tracking velocimetry (PTV) have been used for near-wall velocity measurements in a spark-ignition direct-injection single cylinder engine. A 527-nm dual cavity green Nd:YLF laser was used for velocity measurements near the cylinder head wall between the intake and exhaust valves in the tumble mean flow plane parallel to the cylinder axis. A long-distance microscope was used to obtain a spatial resolution of 45 μm. Flow fields were determined from 180 to 490 CAD in the compression and expansion strokes. The data show significant variation in the flow during the compression and expansion strokes and from cycle to cycle. Flow deceleration was observed during the end of the compression that continued during the expansion stroke until 400 CAD when the flow direction reverses. Sub-millimeter-sized vortical structures were observed within the boundary layer over extended periods of time.