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The diesel combustion process involves complex physical and chemical processes. Given this complexity it is not surprising that a wide range of fuel effects on emissions are reported in the literature. In the European Auto/Oil study the EPEFE programme showed that interactions between fuel and engine hardware could partially explain the observed emissions effects. Variations in fuel physical properties can lead to variations in injection timing, fuel delivery, exhaust gas recirculation (EGR) and other parameters. To understand fuel effects on emissions it is clear that we need to separate these different mechanisms. In this programme a modem, electronically controlled, direct-injection (DI) passenger car engine has been studied using a sophisticated test bed system which makes it possible to monitor and control all key engine variables. Seven fuels were tested, including four varying in density and poly-aromatics content taken from the EPEFE programme.

Sandia National Laboratories has been investigating a new, integrated approach to generating electricity with ultra low emissions and very high efficiency for low power (30 kW) applications such as hybrid vehicles and portable generators. Our approach utilizes a free piston in a double-ended cylinder. Combustion occurs alternately at each cylinder end, with intake/exhaust processes accomplished through a two stroke cycle. A linear alternator is mounted in the center section of the cylinder, serving to both generate useful electrical power and to control the compression ratio by varying the rate of electrical generation. Thus, a mechanically simple geometry results in an electronically controlled variable compression ratio configuration. The capability of the homogeneous charge compression ignition combustion process employed in this engine with regards to reduced emissions and improved thermal efficiency has been investigated using a rapid compression expansion machine.

Lower explosion limits (LEL) and the chemical compositions of JP-8, Jet A and JP-5 fuel vapors were determined in a sealed combustion vessel equipped with a spark igniter, a gas-sampling probe, and sensors to measure pressure rise and fuel temperature. Ignition was detected by pressure rise in the vessel. Pressure rises up to 60 psig were observed near the flash points of the test fuels. The fuel vapors in the vessel ignited from as much as 11°F below flash-point measurements. Detailed hydrocarbon speciation of the fuel vapors was performed using high-resolution gas chromatography. Over 300 hydrocarbons were detected in the vapors phase. The average molecular weight, hydrogen to carbon ratio, and LEL of the fuel vapors were determined from the concentration measurements. The jet fuel vapors had molecular weights ranging from 114 to 132, hydrogen to carbon ratios of approximately 1.93, and LELs comparable to pure hydrocarbons of similar molecular weight.

In his paper “The Knock Syndrome - its Cures and its Victims” (SAE 841339) Oppenheim proposed to change the whole process of the internal combustion engine replacing moving flames by homogeneous and simultaneous combustion. Intensive research work on flame propagation and auto-ignition phenomena led to new insights into combustion over recent years. The implementation of auto-ignition on two-stroke S.I. engines revealed the potential for simultaneous reductions in fuel consumption and NOx emission. Deploying the principle for the four-stroke piston engine and standard fuel would provide optimum conditions for application in common vehicles. The basic problem of homogeneous combustion is presented and some options of control are discussed. A methodology is proposed to apply a new type of combustion simply through a consistent combination of modern technology available for the S.I. engine.

The uniform lean gasoline-air mixture was provided to diesel engine and was ignited by direct diesel fuel injection. The mixing region that is formed by diesel fuel penetration and entrainment of ambient mixture is regarded as combustible turbulent jet. The ignition occurs in this region and the ambient lean mixture is burned by flame propagation. The lean mixture of air-fuel ratio between 150 and 35 could be ignited and burned by this ignition method. An increase of diesel fuel injection is effective to ensure combustion and ignition. As diesel fuel injection increases, HC concentration decreases, and NOx and CO concentration increases.

This research focused on the light emission behavior of the OH radical (characteristic spectrum of 306.4 nm) that plays a key role in combustion reactions, in order to investigate the influence of the residual gas on autoignition. The test engine used was a 2-stroke, air-cooled engine fitted with an exhaust pressure control valve in the exhaust manifold. When a certain level of internal EGR is forcibly applied, the temperature of the unburned end gas is raised on account of heat transfer from the hot residual gas and also due to compression by piston motion. As a result, the unburned end gas becomes active and autoignition tends to occur.

Lean burn gas engines are expected to reduce NOx emission while improving engine performances such as output and thermal efficiency. Recently, an ignition method using a small quantity of diesel fuel (pilot fuel) as an ignition source for lean-burn gas engines has introduced further improvement of their performance. Generally, this method has been used for pre-chamber engines because it could not successfully lead to reduce NOx and Particulate emissions when adopted for open-chamber engines. However, the possibility of improvement of performances of open-chamber engines with this ignition method has also been expected(1). An experimental study was conducted to investigate the performance of an open-chamber gas engine with pilot fuel for ignition source. Experiments were conducted by using a single cylinder gas engine equipped with a common-rail injection system.

The effect of external EGR on knock was evaluated using a CFR engine. Combustion pressure was sampled on a time basis. A band pass filter in the time domain was applied to the pressure cycles. Five knock indices were calculated for each combustion cycle. The problem to quantify knock intensity was focused. At this extent measurements were carried out on standard isooctane-n-heptane blends in the test conditions used for the determination of the Motor Method Octane Number (MON). Knock intensity was varied acting on compression ratio. For each index, the conditions of absence of knock were determined using motored cycles. The indices were compared and one of them, showing the lowest C.O.V., was selected for further measurements. The effect of EGR on test fuels having different composition was evaluated varying the compression ratio, at fixed ignition timing. In this way, the same level of detonation, obtained in the absence of EGR, was realized with different amount of external EGR.

Several knock-detection methods, based both on cylinder pressure analysis and on engine block vibration analysis, have been carefully scrutinized through a critical review of the knock-detection techniques available in literature. Issues have been discussed regarding the physical meaning of knock intensity measurement indexes, mechanical noise sensitivity, transducer type and location, filtering-frequency bands and crank-angle window selection. An experimental investigation has been carried out on a typical European mass-produced engine, and this has provided criteria for the selection of the most suitable and reliable techniques, and has allowed a comparison between experimental results obtained by means of different knock-detection methods.

Combustion information from three combustion chamber geometries was analyzed: Pancake and horseshoe geometry on a single-cylinder research engine, and pentroof geometry in a turbocharged four-cylinder production engine. Four different fuels were used. In the horseshoe configuration, the cylinder pressure traces from the burnt gas and from the end-gas pocket were evaluated. It is shown that the characteristics of knock are to a large degree a function of the combustion chamber geometry and that they are influenced strongly by the transducer position. It is shown for pentroof geometry that the number of cycles required to properly describe the knock population is a function of the knock intensity. A large error potential is shown for samples smaller than about 100 - 200 consecutive cycles. Good agreement between knock description based on accelerometer data and based on pressure data was found.

The work presented in this paper addresses the effects on combustion of recycling cooled exhaust gas (EGR) to the inlet charge of a standard production, four cylinder 2.3 l turbocharged, SI engine. The effect of various amounts of EGR at different temperatures and ignition timings were investigated. Considerable knock suppression at power output comparable with what was achieved with fuel enrichment, could be achieved by adding cooled EGR. Due to inherent high thermal loads, turbocharged engines have been operated at rich air/fuel-ratios during high load conditions, with subsequent high tailpipe emissions of CO in particular, but also HC. By substituting fuel enrichment with cooled EGR, a stoichiometric charge can be used, thus enabling the use of a three way catalytic converter at all operating conditions.

A Catalytic Hot Wire Probe (CHWP) technique has been developed to estimate local fuel concentration near the spark plug of a 4-valves Spark Ignition Engine. Various levels of gasoline concentrations, stratification and tumble levels have been achieved by modifying the injection and intake valve configurations. To validate this CHWP technique, local fuel concentration was also measured by using an optical diagnostic technique: Planar Laser Fluorescence (PLIF). Comparative results show good agreements, capabilities as well as limitations of both techniques. It can be concluded that CHWP is a minimised intrusive, inexpensive and easy technique which allows the evaluation of cylinder mixture preparation near the spark of an SI engine. This is a promising technique which could be used, in the future, to evaluate the mixture stratification in direct injection engines.

An engine bench test has been developed to measure the total amount of liquid fuel wetting the intake walls of a S.I. port fuel injected engine under steady-state conditions. A four cylinder engine equipped with a double injection system was been utilized. One injection system was fed with 2-methyl-2-butene, which did not produce liquid fuel deposit on the intake manifold, the other injection system was fed with different types of fuel and both systems were set at the stoichiometric air-fuel ratio. Putting the injection commutation on, the 2-methyl-2-butene is suddenly replaced by the fuel of the second injection system. An oxygen sensor (UEGO type) monitors the air-fuel ratio excursion due to the injection commutation and the test runs until the A/F re-establishment at the stoichiometric level.

The quality of air-/fuel-mixture is of prime importance for cycle fluctuations of combustion. Investigations of mixture formation and conditions in SI engines have been subject of intensive research since many years. The scope of this work was to investigate crank angle resolved determination of qualitative and quantitative mixture conditions inside the combustion chamber in dependence on various engine operating conditions. For this experimental investigation a time resolved Gas Sampling Valve (GSV) was combined with a flame ionisation detector (FID), a CO2-analyzer and a mass spectrometer. The GSV also enables the determination of residual gas concentration. Measurements on a DI gasoline engine show influences of air-/fuel-mixture in dependence on various engine operating conditions when the engine runs in charge stratification mode. Moreover, experimental results of local mixture composi-tion are compared with fuel distribution, calculated from CFD-codes.

Liquid fuel flow into the cylinder an important source of hydrocarbon (HC) emissions of an SI engine. This is an especially important HC source during engine warm up. This paper examines the phenomena that determine the inflow of liquid fuel through the intake valve during a simulated start-up procedure. A Phase Doppler Particle Analyzer (PDPA) was used to measure the size and velocity of liquid fuel droplets in the vicinity of the intake valve in a firing transparent flow-visualization engine. These characteristics were measured as a function of engine running time and crank angle position during four stroke cycle. Droplet characteristics were measured at 7 angular positions in 5 planes around the circumference of the intake valve for both open and closed-valve injection. Additionally the cone shaped geometry of the entering liquid fuel spray was visualized using a Planar Laser Induced Fluorescence (PLIF) setup on the same engine.

This paper describes an experimental and numerical investigation studying the steady-state flow generated by a SI-engine intake port on a water analogue test rig. The experimental method utilised was Digital Particle Image Velocimetry(DPIV) which allows the rapid measurement of large areas of the flow. The velocity fields were measured in several planes of a cylindrical glass test section under the intake port. A three dimensional CFD analysis was conducted to numerically determine the flow in the test rig. The goal of the study was to compare and evaluate the results of both methods in order to determine their respective validity and limitations. The theory and procedures used for both the experimental and numerical methods are discussed in detail. A comparison of the resulting flow structures from the DPIV measurements and the CFD analysis showed good qualitative and quantitative agreement between the two methods.

Transient two-dimensional temperature distributions in the compression stroke and in the unburned end-gas of an SI engine were measured employing laser-induced fluorescence (LIF) of a fuel marker that possesses strongly temperature-dependent spectroscopic properties. The use of two different excitation wavelengths simplifies the otherwise complicated relation between LIF signal intensity and system parameters. The temperature fields obtained in this manner can be used to correct measured tracer-LIF maps and thus help to determine fuel distributions. Averaged temperature fields are compared to model calculations based on a homogeneous reactor assumption.

Various fluorescence tracers were assessed for their applicability for simultaneously measuring fuel distributions of different volatility classes. Tracers were chosen to show significantly different boiling behaviour representing three volatility classes of non-fluorescing multi-component fuels. Fluorescence properties of the markers were investigated using a heated static high-pressure cell with respect to emission behaviour, temperature and pressure dependence and quenching influences. A combination of ketonic and aromatic tracers appeared to be ideal for simultaneous imaging purposes since fluorescence is emitted in separate spectral regions with little overlap. Simultaneous measurements of the fuel distribution of two volatility classes were performed in a port fuel injected engine showing significant differences in the fuel distributions of low and mid boiling fractions in early stages of compression.

The presence of liquid fuel inside the engine cylinder is believed to be a strong contributor to the high levels of hydrocarbon emissions from spark ignition (SI) engines during the warm-up period. Quantifying and determining the fate of the liquid fuel that enters the cylinder is the first step in understanding the process of emissions formation. This work uses planar laser induced fluorescence (PLIF) to visualize the liquid fuel present in the cylinder. The fluorescing compounds in indolene, and mixtures of iso-octane with dopants of different boiling points (acetone and 3-pentanone) were used to trace the behavior of different volatility components. Images were taken of three different planes through the engine intersecting the intake valve region. A closed valve fuel injection strategy was used, as this is the strategy most commonly used in practice. Background subtraction and masking were both performed to reduce the effect of any spurious fluorescence.

In this paper an alternative method for collecting laser induced fluorescence (LIF) signals from engines with limited optical access is presented. An endoscopic detection system has been used for LIF visualisation of both gaseous and liquid fluids in a DISI-engine. The use of an endoscope made it possible to monitor parts of the combustion chamber that could not be accessed through the piston with conventional optics. Brief investigations of the signal collection efficiency have been performed on the endoscopic system as well as on a system based upon conventional optics. The technique shows promising results and the use of endoscopic detection systems should be considered as a complement to using advance design quarts piston crowns for conventional detection through the piston.