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Neat dimethyl ether (DME), as an alternative fuel candidate for Diesel engines, was investigated by measuring primarily engine performance and exhaust gas characteristics. In addition, other responses of the engine to the new fuel were also determined at the same time, including the injector needle lift and heat release. The engine measurements with this fuel were compared with those obtained by using conventional Diesel fuel. Findings from the present work include: (1) It was necessary to add a small amount of lubricating additives to DME, if a conventional fuel injection system is employed.

The combustion in a spark ignition engine was studied when it was fueled by neat methanol using the timed injection method at the intake port. The measurements from this fueling were compared with those obtained from a carburetor fueled operation. In the study, results of the cylinder pressure analysis and the in-cylinder high-speed photographic observation showed that the reaction in the timed methanol engine combustion had multiple-stage combustion processes. The multiple-stage reaction was pronounced based on the double spikes in heat release history and droplets individually burning in the mixture. The injection time for the best methanol fueled engine operation seemed to be that right after the intake valve opening when the lowest specific fuel consumption was obtained with smallest cyclic variation in the pressure-time history and when the lowest emissions (NOx, UHC and HCHO) were produced.

The effects of knock with varied intensity on spark-ignition engine performance and emission characteristics were investigated using a single-cylinder CFR engine operated by several different fuels. The variation of knock under a fixed engine speed was obtained by operating the engine using different octane numbers of the fuel and the variation of fuel's octane number was made as follows: For gasoline, two fuels having different octane ratings were used to obtain three different octane-number fuels, 85.3, 87.1, and 88.9; for gasoline/alcohol blend fuels, the volumetric alcohol contents in the blend were 0, 5, and 10% to obtain octane ratings of 85.3, 85.7 and 86.2, respectively; for natural gas (with over 94.5% methane by volume), small different amounts of alcohol were introduced into the stream of gas to produce octane numbers of 116, 118 and 120. For the same fuel, the knock intensity was stronger at lower engine speed and lower with high octane number.

A novel way of using low-cetane-number petroleum gases in a compression ignition (CI) engine is introduced, by directly injecting blends of such fuels with dimethyl ether (DME), a high-cetane-number alternative fuel for low soot emissions. This method both extends advantages of DME and complements its deficiency. Although DME mixes with most hydrocarbon fuels in any ratio, in order to demonstrate the feasibility of the new method and facilitate the analysis, DME-propane blends were investigated in a direct injection CI engine. Some findings of the study are listed. In the engine operated by DME and propane blends, there was no need for significantly increasing the complexity of the fuel system than that employed in the use of neat DME. For the same reason, this method eliminates or minimizes cumbersome hardware necessary when the said gaseous fuels are separately introduced in CI engines.

A single-cylinder direct-injection (DI) Diesel engine (Cummins 903) equipped with a new laboratory-built electronically controlled high injection pressure fuel unit (HIP) was studied in order to evaluate design strategies for achieving a high power density (HPD) compression ignition (CI) engine. In performing the present parametric study of engine response to design changes, the HIP was designed to deliver injection pressures variable to over 210 MPa (30,625psi). Among other parameters investigated for the analysis of the I-IPD DI-CI engine with an HIP were the air/fuel ratio ranging from 18 to 36, and intake air temperature as high as 205°C (400°F). The high temperatures in the latter were considered in order to evaluate combustion reactions expected in an uncooled (or low-heat-rejection) engine for a HPD, which operates without cooling the cylinder. Engine measurements from the study include: indicated mean effective pressure, fuel consumption, and smoke emissions.

Engine combustion behaviors were investigated when the mixture condition at the intake port was varied. This experimental study was performed for several engine variables including types of cylinder head (gas motions), spark plug loction and MBT timing. Among the variables for the mixture condition at induction were the fuel/air mixture ratio (excess air factor) and the portion of atomized liquid fuel out of total fuel in the mixture. The engine operation was analyzed by obtaining the mean effective pressure, thermal efficiency, heat release history, stability of combustion, and lean misfire limit.

In-cylinder flame propagation and its impact on thermal characteristics of the combustion chamber were studied by using a new high-speed spectral infrared imaging system. In this work, successive spectral IR images of combustion chamber events were captured while varying several parameters, including fuel/air, spark timing, speed, and warming-up period. Some investigation of cyclic variation, knock, and high-temperature components during the non-combustion period was also conducted. It was found that the spectral images obtained in both short and long wavelength bands exhibited unique pieces of in-cylinder information, i.e., (qualitative) distributions of temperature and combustion products, respectively. During the combustion period, the temperature of early-formed combustion products continued to increase while the flame front temperature, e.g. near the end gas zone, remained relatively low.

The impact of minutely oxygen-enriched air on spark-ignition (SI) engine combustion was studied by obtaining engine performance measurements and investigating in-cylinder reactions. This study was initiated to determine if development of a new air-cleaner method, which may employ molecular sieve or membrane technology to slightly increase the oxygen concentration in the inducted air, is beneficial for engine operations. The air introduced into a single-cylinder SI engine was added with oxygen to produce oxygen concentrations of 21, 22 and 23%. Some results from engine tests performed with the oxygen enrichment are: The heat release lag, cycle variation and combustion period decreased; substantial reduction of emissions of unburned hydrocarbon emission and noticeable decrease of carbon monoxide were observed; and the brake thermal efficiency and engine output increased.

Reduced emissions from the spark-ignition engine, when fueled by gasoline containing small amounts of MTBE, have led us to explore similar positive results in compression-ignition (CI) engine combustion by adding this oxygenate compound to Diesel fuel. This study was performed in two separate laboratories by employing the respective experimental apparatus. When a pre-chamber type CI engine was operated by using Diesel fuel mixed with several volume portions of MTBE, including 5, 10 and 15%, several positive results were obtained, as compared with those from the baseline neat Diesel-fueled operations: (1) The engine delivers overall comparable or better performance characteristics; (2) The brake thermal efficiency is higher at the advanced and late injection times; (3) Some considerable reduction of both soot and NOx emissions is found; (4) The ignition delay increases but the combustion duration decreases.

Instantaneous successive spectral infrared (IR) images were obtained from a spray plume in a direct injection (DI) type compression-ignition (CI) engine during the compression and combustion periods. The engine equipped with a high pressure electronic-controlled fuel injector system was operated by using D-2 Diesel fuel. In the new imaging system used for the present study, four high-speed IR cameras (with respective band filters in front) were lined up to a single optical arrangement containing three spectral beam splitters to obtain four spectral images at once. Two band filters were used for imaging the water vapor distribution and another two band filters were placed for capturing images of combustion chamber wall or soot formation. The simultaneous imaging was successively triggered by signals from an encoder connected to the engine. The fuel injection parameters were precisely controlled and the pressure-time (p-t) history was obtained for individual sets of images.

With the objective of achieving better investigation of engines-fuels by obtaining instantaneous quantitative imaging of in-cylinder processes, several steps have been taken for some years at Rutgers University. They are: (1) Construction of a new multispectral high-speed infrared (IR) digital imaging system; (2) Development of spectrometric analysis methods; (3) Application of the above to real-world in-cylinder engine environments and simple flames. This paper reports some of results from these studies. The one-of-a-kind Rutgers IR imaging system was developed in order to simultaneously capture four geometrically (pixel-to-pixel) identical images in respective spectral bands of IR radiation issued from a combustion chamber at successive instants of time and high frame rates.

Gas concentrations, under different engine operating conditions, different locations relative to the fuel spray are presented. The gas that is sampled is “snatched” from a continuous flow sampling probe. The time of snatching is controlled. The concentrations of CO, CO2, NOx, and O2 are plotted against, crank position. The sampled gases were analyzed for concentration in the as taken state and after the sampled gas had passed through a heated catalytic oxidation converter. Analysis have been performed and plots are presented of the findings. The analytic procedure developed for the data analysis are presented in detail.

Individual aldehyde (and acetone) emissions were measured from the exhaust gas of a premixed multicylinder spark ignition engine fueled with Indolene and blends of Indolene and either methanol or ethanol. The engine was operated at constant speed (2000 RPM) and MBT spark advance with fuel-air equivalence ratios (Φ) of 0.96, 0.90 and 0.82. During operation at Φ = 0.82, the engine experienced lean-limit misfiring. The DNPH method with a gas chromatographic finish was employed to obtain exhaust gas concentrations of aldehydes and acetone. Also, the methods used in the past for measuring engine exhaust aldehyde and acetone data were compared to each other and briefly discussed. Use of the alcohol blends increased the total aldehyde emission level. Formaldehyde was the largest component, exhibiting a continual increase with increasing alcohol blend level.

The relationship of crevices to the formation of unreacted hydrocarbons in engine combustion remains to be determined. In order to help understand its processes the present paper reports the experimental results obtained from the wall effect on flame propagation in various clearances which were placed in a constant-volume charged with premixed fuel-air gases. The photographic observations revealed that the flame propagation was accelerated in some clearances with both ends open. Furthermore, it was discovered that there is an optimum clearance that creates the most rapid flame propagation through a contained combustible mixture. The smallest optimum clearance was measured in a slightly richer mixture than stoichiometric; the greater clearance was measured in leaner or richer mixtures exhibiting a characteristic quite similar to the dependence of quenching distance to fuel/air ratio. In clearances with one end open the flame propagated slower than outside the clearances.

The present paper considers the processes of incomplete combustion in in-cylinder crevices with clearances slightly greater than quenching distance. For this, an experimental work has been carried out by using a premixed constant-volume combustion chamber. In the chamber, the propagation of flame through the combustible gas contained in individual crevices with various geometries was investigated by two means: high speed schlieren photography to obtain the idiosyncrasy of the in-crevice flame behavior; and fast-response thin-film thermocouples mounted flush with the crevice wall to measure the flame propagation speed, the instantaneous surface temperature, the instantaneous heat flux through the crevice wall, etc. From the investigation, the origins of unburned hydrocarbons formed in the in-cylinder crevices were surmised.

A theoretical model of radiation heat transfer has been developed. A computation of radiation heat flux at a particular location in the combustion chamber by using the present model requires in-cylinder time- and space-resolved species data and cylinder pressure. From the species data, the burned fuel/air ratio distribution is inferred to compute space-resolved adiabatic flame temperature. For the computation of the spectral emissivity of an isothermal volume of adiabatic temperature containing soot, the Rayleigh-limit expression is used. The refraction indices in the expression are obtained by using the dispersion equations based on the electronic theory encompassing both free and bound electrons. For the spectral emissivity from the gaseous component in the volume, the semi-empirical band model is used.

The instantaneous heat transfer through the piston was measured in a motored direct injection-type diesel engine. The engine piston was equipped with a fast-response thermocouple on the surface and at a specified distance below the surface thermocouple at a number of locations. In order to record and process the measurement of temperature and cylinder pressure, a personal computer (PC)-based data acquisition system was connected to the probes, A special linkage device was designed and implemented to connect the thermocouple wires between the bottom of the connecting rod and a stationary point on the oil pan. The surface heat flux was calculated using a one-dimensional conduction model with the measured temperature boundary conditions. The in-cylinder pressure data was used to calculate the cylinder air temperature and the instantaneous film heat transfer coefficient was calculated by using those in-cylinder measurements.

In-cylinder reactions of several internal combustion engine configurations were investigated using a highspeed four-spectral infrared (IR) digital imaging device. The study was conducted with a greater emphasis on the preflame processes by mutually comparing results from different engine-fuel systems. The main features of the methods employed in the study include that the present multi-spectral IR imaging system permits us to capture progressively changing radiation emitted by new species produced in-cylinder fuel-air mixtures prior to being consumed by the heat-releasing reaction fronts. The study of the Diesel or compression-ignition (CI) engine reactions was performed by varying several parameters, e.g. injection pressures, intake air temperature, fuel air ratio, and the start of injection.

In-cylinder reaction processes in a production port-fuel-injection (PFI) spark-ignition engine having optical access were visualized using a high speed four-spectra IR Imaging system. Over one thousand sets of digital movies were accumulated for this study. To conduct a close analysis of this vast amount of results, a new data analysis and presentation method was developed, which permits the simultaneous display of as many as twenty-eight (28) digital movies over a single PC screen in a controlled manner, which is called the Rutgers Animation Program (RAP for short). The results of this parametric study of the in-cylinder processes (including the period before and after the presence of luminous flame fronts) suggest that, even after the engine was well warmed, liquid fuel layers (LFL) are formed over and in the vicinity of the intake valve to which the PFI was mated.

Visualization of in-cylinder reaction processes and performance analysis of a direct-injection Diesel engine equipped with a high injection pressure (HIP) unit were conducted. The study was directed towards evaluation of high-power-density (HPD) engine design strategies, which utilize more intake air operating at rich overall fuel-air ratios. Two separate engine apparatus were used in this study: a Cummins 903 engine and a single-cylinder optical engine equipped with the same family engine components including the cylinder head. The engines were mated with an intensifier-type HIP fuel system fabricated at Rutgers which can deliver fuel injection pressure of over 200 MPa (30,000psi). The one-of-a-kind high-speed four-band infrared (IR) imaging system was used to obtain over fifteen hundred sets of spectral digital movies under varied engine design and operating conditions for the present analysis.