Design Methodology of Centrifugal Automatic Decompression System in Small Gasoline Engine

<div class="htmlview paragraph">To provide fuel/air ratio quantitative measurements in an S.I engines, a transparent cylinder engine is investigated with the Fuel-Air Ratio Laser Induced Fluorescence (FARLIF) technique. In a homogeneous mixture, the two dimensional distribution for the fuel/air ratio is calibrated and measured during the compression stroke for different equivalence ratios. After spark ignition, the combustion zone and the flame front are visualized by laser sheet LIF.</div> <div class="htmlview paragraph">The direct-injection stratified-charge, new concept for gasoline engines is investigated with FARLIF. In the direct injection gasoline engine where the fuel is directly injected into a cylinder and the flow is highly turbulent, two injection timings are used: -early injection (i.e. during the intake stroke) to promote a homogeneous distribution; -late injection during the compression stroke, to generate a ultra-lean stratified charge. While the early fuel injection shows a homogeneous vapor phase during the compression stroke, the late injection shows a stratified mode with the presence of both liquid and vapor phases.</div>

<div class="htmlview paragraph">High exhaust gas recirculation (EGR) tolerance is always pursued not only for its advantages of the pumping loss reduction and fuel economy benefit, but also for stringent emission requirements by using conventional three-way catalytic converter (TWC) instead of costly NOx trap. How to keep fresh charge and EGR separated in the cylinder of a conventional four valve gasoline engine is a critical challenge. This work establishes advanced user subroutines and overall simulation strategies to model engine in-cylinder turbulent flow, temperature, pressure, and EGR concentration fields and to simulate EGR stratification process in a typical pent-roof gasoline engine cylinder during intake and compression strokes.</div> <div class="htmlview paragraph">A series of computational fluid dynamics (CFD) studies - combustion dome, ports, valve and valve mask configurations, EGR tolerances, swirl ratio, boundary and initial conditions, etc., have been conducted to relate the “corndog” flow structure and physical parameters - centrifugal force, heat transfer, swirl ratio, tumble flow, turbulent and burnt gas residual. Based on the CFD results of the four valve-port, pent-roof combustion dome system, the direction to reach the corndog flow structure should be: (1). Reduce the burnt gas residual; (2). Decrease the temperature difference of EGR and air to minimize their heat transfer and centrifugal force; (3). Reduce the turbulent intensity; (4). Design the combustion dome as flat as possible; (5). Avoid using masks; (6). Reduce tumble flow; (7). Keep certain level of swirl ratio.</div> <div class="htmlview paragraph">Another method to stratify EGR in cylinder, named “conjugate vortex EGR stratification” system, has been discovered by the CFD analysis. Two identical inversed helical ports, one intake and another exhaust, are combined together to create two strong inverse gas flow vortices in the cylinder. The double inverse vortices result in a stable separation of in-cylinder fresh charge and EGR flows induced from intake port and exhaust port during the entire intake stroke. A clear stratification interface between the two streams of flow was found and located in the cylinder center. The turbulent kinetic energy at the interface is quite low, indicating that the minimum mixing opportunity between the EGR and fresh charge occurs at this location.</div>

<div class="htmlview paragraph">This paper describes the use of carbon-14 radiolabeled succinimides and succinate esters to investigate the role of ashless dispersants in controlling deposit formation in gasoline engines. Analysis of used oils, varnish deposits, and insolubles from several gasoline engine tests showed that:</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"> <span class="li-label">1.</span> <div class="htmlview paragraph">Ashless dispersants were not significantly broken down chemically in service.</div></li> <li class="list-item"> <span class="li-label">2.</span> <div class="htmlview paragraph">Dispersants played an active role in the processes leading to deposits and were evenly distributed in varnish throughout the engine.</div></li> <li class="list-item"> <span class="li-label">3.</span> <div class="htmlview paragraph">Insolubles in the oil were agglomerations of small, primary particles of about 300-400 diameter.</div></li> <li class="list-item"> <span class="li-label">4.</span> <div class="htmlview paragraph">A major portion of the dispersant in used oils was bound up with polar organic and inorganic species and was unable to assist in dispersing particles.</div></li></ol></div> <div class="htmlview paragraph">The implication of these findings on the development of new additives and crankcase oil formulations is discussed.</div>

<div class="htmlview paragraph">This paper describes a thick film ZrO<sub>2</sub> NOx sensor feasible for diesel and gasoline engine applications, and introduces modification items from the previous concept design.(<span class="xref">1</span>)</div> <div class="htmlview paragraph">The modification items comprise simplifying the sensing element design to reduce output terminals for package design and applying temperature control to the sensing element in order to minimize sensor performance dependency on gas temperature.</div> <div class="htmlview paragraph">The NOx sensor indicates a stable linear signal in proportion to NOx concentration in a wide range of temperature, A/F and NOx concentration as a practical condition on both gasoline and diesel engines. The NOx sensor shows a good response in hundred msec. and a sharp signal following NOx generation in a transient state as well.</div> <div class="htmlview paragraph">Besides, another type of a NOx sensor is proposed for low NOx measurement in a practical use, by an electromotive force(EMF) voltage instead of a pumping current.</div>

<div class="htmlview paragraph">During last four years the authors were involved in the simulation and investigation of combustion and ionization in the cylinder of gasoline and natural gas Spark Ignition (SI) engine. Two-zone model of combustion and chemical non-equilibrium ionization and results of the numerous numerical investigation were presented by the authors at SAE 2002 and SAE 2003 World Congresses. This model and numerical results provided an important insight into combustion products behavior and gave the chance to find correlation between chemical and thermal ionization of combustion products and SI engine performances.</div> <div class="htmlview paragraph">In order to provide better correspondence of the numerical data to the experimental results in the wide range of operational parameters for different geometry of engines a new three-zone model was developed and successfully tested. In comparison with previous one new model includes the additional third zone, which simulates the processes in the small volume of flame kernel inside the gap between spark plug electrodes.</div> <div class="htmlview paragraph">Following processes in the flame kernel are taken into account:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"><div class="htmlview paragraph">detailed mechanism of chemical interaction including chemical and thermal ionization;</div> </li> <li class="list-item"><div class="htmlview paragraph">heat exchange between combustion products and electrodes;</div> </li> <li class="list-item"><div class="htmlview paragraph">mass exchange between third zone and combustion products in the cylinder.</div> </li> </ul> </div> <div class="htmlview paragraph">The comparison of numerical and experimental results showed more accurate correlation between measured and calculated values of pressure and ion current. The concentration of electrons in the gap between spark plug electrodes corresponds better to the experimental data for gasoline engines in comparison with two-zone model. Three-zone model became a new generation among the models for the investigation of in-cylinder combustion products ionization and simulation of operational and ecological performances of SI engine.</div>

<div class="htmlview paragraph">Since ethanol is a renewable source of energy and it contributes to lower CO2 emissions, ethanol produced from biomass is expected to increase in use as an alternative fuel. It is recognized that for spark ignition (SI) engines ethanol has advantages of high octane number and high combustion speed and has a disadvantage of difficult startability at low temperature.</div> <div class="htmlview paragraph">This paper investigates the influence of ethanol fuel on SI engine performance, thermal efficiency, and emissions. The combustion characteristics under cold engine conditions are also examined.</div> <div class="htmlview paragraph">Ethanol has high anti-knock quality due to its high octane number, and high latent heat of evaporation, which decreases the compressed gas temperature during the compression stroke. In addition to the effect of latent heat of evaporation, the difference of combustion products compared with gasoline further decreases combustion temperature, thereby reducing cooling heat loss. As a result, torque and thermal efficiency increase compared to gasoline. Also, reductions in CO2, NOx, and THC are described.</div> <div class="htmlview paragraph">To improve combustion under cold conditions, methods of increasing fuel temperature or the compressed gas temperature during the compression stroke are considered. In the latter case, simulation showed valve timing to be effective. Based on simulation results, the effect of valve timing optimization on improving combustion at low temperature is investigated with an engine.</div>

<div class="htmlview paragraph">A new methodology for rapidly characterizing the in-cylinder flow field at spark ignition for internal combustion engines is described in this paper. The process involves the use of 3-D particle tracking velocimetry to measure the flow field at intake valve closing (IVC) in a water analog engine simulation, and the use of CFD to compute the evolution of the measured flow field during the compression stroke, by using the experimental 3-D PTV results at IVC as the initial condition for the calculations.</div> <div class="htmlview paragraph">The technique has been applied to investigate the in-cylinder flow field of a typical 4 valve engine operating in two different modes; one or two intake ports active. The results indicate that in either mode the flow field at IVC is dominated by a different large scale structure: tumble in the case where both intake ports are active and swirl in the case where only one port is active. The results also indicate that these structures evolve differently during the compression stroke. While swirl decays monotonically during the compression stroke, tumble appears to gain in strength during the early stages of the compression before it starts decaying at a faster rate.</div> <div class="htmlview paragraph">In addition, an initial comparison of the results obtained by this hybrid approach with engine combustion data indicates that the burn rate increases with increasing levels of in-cylinder turbulence, which is the expected trend based on combustion entrainment models.</div>

<div class="htmlview paragraph">Referring to the McKeen gasoline-driven car and one of the gasoline-electric type that were introduced in the early part of the present century and were the pioneers among self-propelled cars for railroad use, the author ascribes their limited success to their excessive weight and to engine and transmission troubles. Both these types, he thinks, might have been developed successfully had the gasoline engine been in its present state of efficiency and reliability.</div> <div class="htmlview paragraph">The early attempts having been more or less unsuccessful, the construction of all types was discontinued during the war. More recently the progress in the design and construction of highway motor-trucks has caused them to be adapted to railroad service by applying flanged tires to the rear wheels, pivotal pony-trucks forward and a motorbus body for the carrying of passengers and a limited amount of baggage. These motorbus-type cars weigh approximately 500 lb. per passenger as compared with 1500 lb. in the cars originally used and can be maintained with the same ease and at less expense than can a highway motor-truck. But, although these cars were economical, they were not comfortable to ride in, and they have been superseded by slightly larger cars of light weight equipped with the same automotive-type engine but with two pairs of four-wheel pivotal trucks and swing bolsters. This is the type largely in use at present.</div> <div class="htmlview paragraph">About 3 years ago an investigation of self-propelled cars in this Country and in Europe was made by the American Short Line Railroad Association, 500 questionnaires being sent to members of the Association in this Country and in Canada; and many valuable data were acquired regarding the operation of motor cars on short lines and branch lines under all sorts of conditions. The records show that at present 135 roads are operating 164 motor cars, of which 34 are on trunk lines and 130 on short lines. The approximate mileage is 8000. The number of steam trains that have been replaced is 200. One steam road, 108 miles in length, that showed a deficit of $36,000 per year showed a profit of more than $22,000 during the first year of operation with motor cars. The total investment in serviceable rail motor-cars at present is about $2,500,000; the steam-train investment necessary to provide the same service would be from $8,000,000 to $10,000,000.</div> <div class="htmlview paragraph">It is the author's opinion that eventually all branch lines and short lines will become motorized, the limiting factors at present being the inadequate power developed by the most approved type of motor-truck engine. A lower grade of fuel than gasoline will, no doubt, also be found eventually, which will make available a type of internal-combustion locomotive for handling freight service. Increasing the size of the engine will probably require some change in the form of the transmission, for the limit of the present clutch and transmission system has almost been reached. But this may prove to be an advantage.</div> <div class="htmlview paragraph">Among the other economies accruing to the use of the self-propelled vehicle would be the abolition of such facilities as water-stations, coal-stations, roundhouses and the like. The cost of maintenance of the road-bed would also be reduced.</div> <div class="htmlview paragraph">With the further development of automotive equipment the complete motorization of short-line and branch-line railroads may be expected to turn the present operating deficits into profits.</div> <div class="htmlview paragraph">Tables are appended showing the operating statement of a motor car for 1 year and an analysis of the operating cost during this period.</div>

<div class="htmlview paragraph">Controlled Auto-Ignition (CAI) combustion, also known as HCCI or PCCI, has recently emerged as a viable alternative combustion process to the conventional spark ignition (SI) or compression ignition (CI) process for internal combustion (IC) engines, owing to its potential for high efficiency and extremely low emissions. One of the most effective and practical means of achieving CAI combustion in an engine is to retain or recycle the burnt gases. In order to understand better the effects of recycled burnt gases on CAI combustion, detailed analytical and experimental studies have been carried out. The analytical studies were performed using an engine simulation model with detailed chemical kinetics.</div> <div class="htmlview paragraph">The five effects of the recycled burned gases studied include:</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"><span class="li-label">(1.)</span><div class="htmlview paragraph">Charge heating effect: higher intake charge temperature due to hot burned gases;</div></li> <li class="list-item"><span class="li-label">(2.)</span><div class="htmlview paragraph">Dilution effect: the reduction of oxygen due to the presence of the burned gases;</div></li> <li class="list-item"><span class="li-label">(3.)</span><div class="htmlview paragraph">Heat capacity effect: due to higher specific heat capacity of burned gases;</div></li> <li class="list-item"><span class="li-label">(4.)</span><div class="htmlview paragraph">Chemical effect: chemical reactions involving CO<sub>2</sub> and H<sub>2</sub>O in the burned gases</div></li> <li class="list-item"><span class="li-label">(5.)</span><div class="htmlview paragraph">Stratification effect: recycled burned gases are stratified from the fuel/air mixture.</div></li> </ol> </div> <div class="htmlview paragraph">And the main conclusions are:</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"><span class="li-label">(1.)</span><div class="htmlview paragraph">The charge heating effect is mainly responsible for the advanced AI timing due to hot burned gases. It increases the heat release rate and shortens the combustion duration.</div></li> <li class="list-item"><span class="li-label">(2.)</span><div class="htmlview paragraph">The dilution effect does not affect AI timing, but it extends combustion duration. Its slows down the heat release rate only when large amount of burned gases is present.</div></li> <li class="list-item"><span class="li-label">(3.)</span><div class="htmlview paragraph">The heat capacity effect is mainly responsible for the reduction in the heat release rate, and it has a similar effect to extend the combustion duration as the dilution effect.</div></li> <li class="list-item"><span class="li-label">(4.)</span><div class="htmlview paragraph">The chemical effect does not affect AI timing and heat release rate. It reduces the combustion duration slightly at high concentrations of burned gases.</div></li> <li class="list-item"><span class="li-label">(5.)</span><div class="htmlview paragraph">The stratified burned gases facilitate the CAI combustion due to the presence of higher temperature region at the boundary between of the hot burned gases and combustible charge.</div></li> </ol> </div>

<div class="section abstract"><div class="htmlview paragraph">As the efforts to push capabilities of current engine hardware to their durability limits increases, more accurate and reliable analysis is necessary to ensure that designs are robust. This paper evaluates a method of Conjugate Heat Transfer (CHT) analysis for a gasoline and a diesel engine that combines combustion Computational Fluid Dynamics (CFD), engine Finite Element Analysis (FEA), and cooling jacket CFD with the goal of obtaining more accurate temperature distribution and heat loss predictions in an engine compared to standard de-coupled CFD and FEA analysis methods. This novel CHT technique was successfully applied to a 2.5 liter GM LHU gasoline engine at 3000 rpm and a 15.0 liter Cummins ISX heavy duty diesel engine operating at 1250 rpm. Combustion CFD simulations results for the gasoline and diesel engines are validated with the experimental data for cylinder pressure and heat release rate. Radiation models were implemented to estimate heat transfer more accurately for diesel engine. FEA simulations are performed in a separate software platform. Data exchanges between CFD and FEA software codes are performed at specified sub-cycle engine intervals and the simulations are continued for multiple engine cycles until cycle-to-cycle convergence of wall temperatures is achieved. The model predictions are validated against experimental data available from thermocouples embedded inside the cylinder head. The detailed CHT model includes the coolant circuit and oil gallery. The overall predictions from the model match closely with the experimental observations. The work establishes a validated modeling framework for CHT modeling in gasoline and diesel engines.</div></div>

<div class="section abstract"><div class="htmlview paragraph">In recent years, emission regulations have been getting increasingly strict. In the development of engines that comply with these regulations, in-cylinder pressure plays a fundamental role, as it is necessary to analyze combustion characteristics and control combustion-related parameters. The analysis of in-cylinder pressure data enables the modelling of exhaust emissions in which characteristic temperature can be derived from the in-cylinder pressure, and the pressure can be used for other investigations, such as optimizing efficiency and emissions through controlling combustion.</div><div class="htmlview paragraph">Therefore, a piezoelectric pressure sensor to measure in-cylinder pressure is an essential element in the engine research field. However, it is difficult to practice the installation of this pressure sensor on all engines and on-road vehicles owing to cost issues. Therefore, there have been several studies aiming to estimate the in-cylinder pressure using only the data available from the Engine Control Unit (ECU) without an additional pressure sensor.</div><div class="htmlview paragraph">An in-cylinder pressure prediction model for conventional light-duty diesel engines had been established by authors and described in this paper. First, the pressure during the compression stroke was estimated using a variable polytropic index. Next, the Wiebe function was applied to describe pressure during pilot and main combustion. This prediction of the in-cylinder pressure was established for real-time estimation.</div><div class="htmlview paragraph">The complete pressure prediction model consists of subordinate models, where physical phenomena are simplified for the real-time application of the model. The accuracy of the submodels has a direct influence on the error in the parent model the pressure prediction. Therefore, sensitivity analysis was conducted in this study to verify the effect of the submodels, including the polytropic index model, ignition delay model, heat loss model and combustion duration model, on the entire pressure prediction model. This study will contribute to establishing a more accurate pressure prediction through sensitivity analysis and will be useful to many studies that require in-cylinder pressure information.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The aim of this work is to investigate the possibility of heat insulation by “Temperature Swing”, that is temperature fluctuation, on combustion chamber walls coated with low-heat-conductivity and low-heat-capacity materials.</div><div class="htmlview paragraph">Adiabatic engines studied in the 1980s, such as ceramic coated engines, caused constantly high temperature on combustion wall surface during the whole cycle including the intake stroke, even if it employed ceramic thermal barrier coating methods. This resulted in increase in NOx and Soot, decrease in volumetric efficiency and combustion efficiency, and facilitated the occurrence of engine knock.</div><div class="htmlview paragraph">On the other hand, “Temperature Swing” coat on the combustion chamber walls leads to a large change in surface temperature. In this case, the surface temperature with this insulation coat follows the transient gas temperature, which decreases heat loss with the prevention of intake air heating, and also which is expected to prevent NOx and Soot from increasing. In our calculations, the increase of the surface temperature fluctuation, “Temperature Swing” results from the coat of lower heat conductivity and lower heat capacity. Particularly in Gasoline engines, the coat with the appropriate thickness can reduce the heat flux from the wall to the working gas during intake stroke and can avoid engine knock.</div><div class="htmlview paragraph">Based on our calculations, it is clarified that both the prevention of intake air heating and the low heat rejection were successfully possible with the material of appropriate thermo-physical properties.</div><div class="htmlview paragraph">In addition to the calculations, a preliminary test-piece experiment was executed. It was demonstrated that the surface temperature of a porous coat, that is a candidate of “Temperature Swing” coat, immediately follows the transient gas temperature, and also the proposed insulation coat can exactly reduce the heat flux in the single-cylinder engine.</div></div>

<div class="htmlview paragraph">Current and proposed legislation regarding gaseous emissions has adversely affected the fuel economy of certain gasoline engines. Recent economic and environmental developments such as the fossil fuel shortage have improved the potential for the use of diesel engines as the power plant for small commercial vehicles and possibly certain passenger cars.</div> <div class="htmlview paragraph">Many variables affect fuel economy comparisons. Most of these variables can be associated with either the vehicle design or operation.</div> <div class="htmlview paragraph">The objectives of this paper are to relate fuel economy claims with a variety of cycles and to show how some of these claims can be justified. Also, to show how some of the more impressive diesel over gasoline economy claims relate more to the real world than comparisons based on EPA and SAE cycles.</div> <div class="htmlview paragraph">EPA originally started with one cycle and later split it into city and highway driving, to better cover the real world. SAE now has three cycles which represent a broader range of habits and requirements. There is still room for improvements at the low speed, short trip in cold weather, end of the scale. Also, the high volume of small Commercial vehicles such as Pick-Ups, Vans, Taxis, etc. need attention.</div> <div class="htmlview paragraph">To appreciate the significance of comparing the real world to SAE cycles, we must be familiar with “typical vehicle fuel economy as influenced by trip length” (<span class="xref">1</span>) <span class="xref">*</span>, “fuel savings potentials in short trip cold weather service” (<span class="xref">2</span>), and “other published statistics” (<span class="xref">3</span>) that have SAE level research and credibility.</div> <div class="htmlview paragraph">These papers show the results of surveys describing how up to 80% of trips and 50% of the auto fuel consumed are associated with trips of 10 miles or less.</div>

<div class="section abstract"><div class="htmlview paragraph">All internal combustion piston engines emit solid nanoparticles. Some are soot particles resulting from incomplete combustion of fuels, or lube oil. Some particles are metal compounds, most probably metal oxides. A major source of metal compound particles is engine abrasion. The lube oil transports these abraded particles into the combustion zone. There they are partially vaporized and ultrafine oxide particles formed through nucleation [<span class="xref">1</span>]. Other sources are the metallic additives to the lube oil, metallic additives in the fuel, and debris from the catalytic coatings in the exhaust-gas emission control devices. The formation process results in extremely fine particles, typically smaller than 50 nm. Thus they intrude through the alveolar membranes directly into the human organism. The consequent health risk necessitates a careful investigation of these emissions and effective curtailment.</div><div class="htmlview paragraph">Substantial information is available on diesel engine particulate emissions [<span class="xref">2</span>, <span class="xref">3</span>, <span class="xref">4</span>] but less for SI engines. Beside an example of metal oxide particles from a diesel engine, the present paper shows preliminary results of nanoparticles emissions of SI engines.</div><div class="htmlview paragraph">Four SI engines were investigated: two older and two newer engines, comprising two car engines and two motorbikes. The tests were done on standard transient driving cycles, and steady-state at constant 50 km/h and idling. Prior investigations observed, especially during idling, high concentrations of metal oxide particles [<span class="xref">2</span>]. All tests were done with particle samples collected from the CVS tunnel, during a long operating period, to have sufficient material for analyzing the composition. At the steady-state points, the particle size spectra were measured.</div><div class="htmlview paragraph">The results show that the older SI engines emit high concentrations of soot particles and metal oxide (= ash) particles. The size distribution is decisively bimodal for both soot and ash particles.</div><div class="htmlview paragraph">The newer engines' emission results are less uniform and the concentrations lower, as expected. Altogether, the concentrations of these metal oxide particles are so high, that more detailed investigations are recommended.</div></div>

<div class="section abstract"><div class="htmlview paragraph">A 300 cc gasoline engine has been experimentally and numerically studied to compare PFI and DI operation on naturally-aspirated and turbocharged full load operating points. Experiment outlines the benefits from DI operation in terms of volumetric efficiency, fuel economy and knock propensity but also clearly indicates worse raw engine-out CO emissions. The latter is an indication of the survival of a large scale mixture heterogeneity in this downsized GDI engine even when early injection and intense induced fluid motion are combined.</div><div class="htmlview paragraph">For such a full load operation, the application of optical diagnostics to study mixture heterogeneity cannot be considered because pressure and temperature exceed sustainable levels for transparent materials. Therefore, 3D CFD RANS computations of the intake, injection, combustion and pollutant formation processes including detailed chemistry information are performed to complement the experimental data. The results at the end of compression stroke confirm the existence of a large scale mixture stratification. Moreover, the degree of mixture stratification can be directly related to the measured CO emissions. Combustion and pollutant formation modeling with detailed chemistry information allows quantifying the influence of locally rich mixtures on flame propagation and post-flame chemistry (CO and NO<sub>x</sub> emissions).</div><div class="htmlview paragraph">Computations for various injection timings on a unique operating point explain why the experimentally chosen injection timing is optimal. The interaction of intake-induced fluid motion with injection-induced fluid motion gives rise to a trade-off between turbulence and mixture homogeneity near TDC. Increased turbulence favors combustion speed and reduces knock propensity, which should lead to a better efficiency. But the gain in turbulence is counter-balanced by an enlarged mixture heterogeneity producing larger CO emissions and therefore impeding global efficiency.</div></div>