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Technical Paper

Total Cylinder Sampling from a Diesel Engine (Part II)

An improved system for total cylinder sampling from an indirect injection passenger car type diesel engine has been developed. The system utilizes explosively actuated cutters which cut aluminum diaphragms in both the main combustion chamber and precombustion chamber at a predetermined time. The cylinder charge is rapidly cooled and diluted as it flows from the chambers into the sampling system. When sampling from near top dead center, cylinder pressure decay half times of about 0.5 ms have been achieved. The system has been used to determine NOx concentrations in the cylinder as a function of crankangle position at 1000 rpm with equivalence ratios of 0.32, 0.52, and 0.60. NOx concentrations rise rapidly shortly after the onset of combustion, attain maxima which are 2 to 10% higher than corresponding exhaust concentrations at about 5-10 crankangle degrees after the end of the fuel injection process and then slowly decay to exhaust levels.
Technical Paper

Total Cylinder Sampling from a Diesel Engine

A dumping apparatus has been developed and tested for total cylinder sampling from an indirect injection diesel engine. The apparatus design is described in detail along with the experimental system. The system performance is given for one engine operating condition. Graphs of main chamber and pre-chamber pressures versus crankangle are also included. The system demonstrated a sampling accuracy of ±2 degrees of crankangle.
Technical Paper

Synchronous, Simultaneous Optimization of Ignition Timing and Air-Fuel Ratio in a Gas-Fueled Spark Ignition Engine

A two-dimensional optimization process which simultaneously adjusts the spark timing and air-fuel ratio of a lean-burn natural gas fueled engine has been demonstrated. This has been done by first mapping the thermal efficiency against spark timing and equivalence ratio at a single speed and load combination to obtain the 3-D surface of efficiency versus the other two variables. Then the ability of the control system to find and hold the combination of timing and air-fuel ratio which gives the highest thermal efficiency was explored. The control system described in SAE Paper No. 940546 was used to map the thermal efficiency versus equivalence ratio and ignition timing. NOx, CO, and HC maps were also obtained to determine the tradeoffs between efficiency and emissions. A load corresponding to a brake mean effective pressure of 0.467 MPa was maintained by a water brake dynamometer. A speed of 2000 rpm was maintained by a fuel-controlled governor.
Technical Paper

Particle and Gaseous Emission Characteristics of a Formula SAE Race Car Engine

The focus of this work was the physical characterization of exhaust aerosol from the University of Minnesota Formula SAE team's engine. This was done using two competition fuels, 100 octane race fuel and E85. Three engine conditions were evaluated: 6000 RPM 75% throttle, 8000 RPM 50% throttle, and 8000 RPM 100% throttle. Dilute emissions were characterized using a Scanning Mobility Particle Sizer (SMPS) and a Condensation Particle Counter (CPC). E85 fuel produced more power and had lower particulate matter emissions at all test conditions, but more fuel was consumed.
Technical Paper

Particle Concentrations in a Diesel Cylinder: Comparison of Theory and Experiment

Soot formation and oxidation within the cylinder of a divided-chamber diesel engine have been studied experimentally and predicted analytically using a diesel combustion model. Experimental measurements of in-cylinder particle concentration were made using a unique sampling system which samples and quenches nearly the entire contents of the cylinder on a time scale of less than 1 ms. The experimental measurements are compared with predictions made using a stochastic combustion model coupled to an Arrhenius-type soot formation model, and 02 and OH soot oxidation models. Five engine conditions: low-load standard-timing (base case), high-load standard-timing, low-load advanced-timing, low-load standard-timing + EGR, and low-load standard-timing + 02, were examined experimentally, but only the first three were modeled.
Technical Paper

Measurement of Cyclic Variability in a Diesel Engine Using a Single Cycle Sampler

A system that allows collection and analysis of all of the exhaust from individual engine cycles has been built. Its development and performance are described. The system was used to study the cyclic variability of a 0.7 liter direct injection diesel cylinder operating at 1500 rpm and an equivalence of 0.6. Particulate emissions exhibited the greatest variability. The cyclic variability (standard deviation) of particulate emissions associated with in-cylinder processes was found to be about 40% of the mean. The variability of NOx emissions that could be associated with in-cylinder processes was much lower, only about 6% of the mean. The variability of pressure development in the combustion process itself, as indicated by IMEP, was very low, less than 2% of the mean.
Technical Paper

Investigation of a Diesel Exhaust Aerosol

This paper describes a study of the exhaust aerosols produced by a single cylinder Onan diesel engine using a rapid dilution sampling system. Diluted exhaust aerosols were analyzed with an electrical aerosol analyzer (EAA) and a transmission electron microscope. Mass concentrations of particulate matter were determined by gravimetric filter analysis. Volume mean diameters observed with the EAA were about 0.1 μm. Mass concentration measurements made with filters were in qualitative agreement with those calculated from the aerosol volume concentrations measured with the EAA.
Technical Paper

Influence of an Iron Fuel Additive on Diesel Combustion

This program used a 0.6 liter DI NA single cylinder diesel engine to study the influence of ferrocene as a fuel additive on particulate and NOx emissions and heat release rates. Previous Studies1,15 have shown efficiency and particulate emission benefits only after engine conditioning. Two engine configurations were tested: standard aluminum piston with normal engine deposits and a second test with the engine cleaned to “new engine condition”, but with the piston replaced with a thermal barrier coated piston. Particle concentration and size in roughly the 7.5 to 750 nm diameter range were measured with a condensation nucleus counter and an electrical aerosol analyzer. Heat release rates and IMEPs were calculated from in-cylinder pressure data. Particle number concentrations increased substantially when the 250 ppm dose was first started with both engine configuration, but decreased 30% to 50% with conditioning.
Technical Paper

Fumigation of a Diesel Engine with Low Btu Gas

A 0.5 liter single-cylinder, indirect-injection diesel engine has been fumigated with producer gas, a mixture of principally H2, CO, and N2 with a heating value of about 160 Btu/ft3. Producer gas is produced by air-blown gasification of coal or biomass. Measurements of power, efficiency, cylinder pressure, and emissions were made. At each operating condition, engine load was held constant, and the gas-to-diesel fuel ratio was increased until abnormal combustion (severe efficiency loss, missfire, knock, or preignition) was encountered. This determined the maximum fraction of the input energy supplied by the gas, Emax, which was found to be dependent upon injection timing and load. At light loads, Emax was limited by severe efficiency loss and missfire, while at heavy loads it was limited by knock or preignition.
Technical Paper

Emissions Characteristics of Soy Methyl Ester Fuels in an IDI Compression Ignition Engine

As part of an ongoing program to control the emissions of diesel-powered equipment used in underground mines, the U. S. Bureau of Mines evaluated exhaust emissions from a compression ignition engine using oxygenated diesel fuels and a diesel oxidation catalyst (DOC). The fuels include neat (100%) soy methyl ester (SME), and a blend of 30% SME (by volume) with 70% petroleum diesel fuel. A Caterpillar 3304 PCNA engine was tested for approximately 50 hours on each fuel. Compared with commercial low-sulfur diesel fuel (D2), neat SME increased volatile organic diesel particulate matter (DPM) but greatly decreased non-volatile DPM, for a net decrease in total DPM. The DOC further reduced volatile and total DPM NOx emissions were slightly reduced for the case of neat SME, but otherwise were not significantly affected. Peak brake power decreased 9% and brake specific fuel consumption increased 13 to 14% for the neat methyl soyate because of its lower energy content compared with D2.
Technical Paper

Effect of Alcohols as Supplemental Fuel for Turbocharged Diesel Engines

Alcohols are examined as supplemental carbureted fuels for highspeed turbocharged diesels as typified by the White Motor/Waukesha F310 DBLT (6 cylinder, 310 cu. in.). Most of the work was with methanol; ethanol and isopropanol were compared at a few points. Fumigation (dual-fueling) with alcohol significantly reduced smoke and intake manifold temperature. These effects were largest at high load. Efficiency and HC emissions were essentially unchanged. Cylinder pressures and rise rates were examined for possible adverse effects on engine structure. The range of speed and load favorable to alcohol dual-fueling are such that, should alcohols become economically competitive as fuels, a practical duel-fuel system could be applied to existing diesel engines.
Technical Paper

Driving Down On-Highway Particulate Emissions

It has been reported that particulate emissions from diesel vehicles could be associated with damaging human health, global warming and a reduction in air quality. These particles cover a very large size range, typically 3 to 10 000 nm. Filters in the vehicle exhaust systems can substantially reduce particulate emissions but until very recently it was not possible to directly characterise actual on-road emissions from a vehicle. This paper presents the first study of the effect of filter systems on the particulate emissions of a heavy-duty diesel vehicle during real-world driving. The presence of sulfur in the fuel and in the engine lubricant can lead to significant emissions of sulfate particles < 30 nm in size (nanoparticles).
Technical Paper

Diesel Exhaust Particle Size: Measurement Issues and Trends

Exhaust particle number concentrations and size distributions were measured from the exhaust of a 1995 direct injection, Diesel engine. Number concentrations ranged from 1 to 7.5×107 particles/cm3. The number size distributions were bimodal and log-normal in form with a nuclei mode in the 7-15 nm diameter range and an accumulation mode in the 30-40 nm range. For nearly all operating conditions, more than 50% of the particle number, but less than 1% of the particle mass were found in the nuclei mode. Preliminary indications are that the nuclei mode particles are solid and formed from volatilization and subsequent nucleation of metallic ash from lubricating oil additives. Modern low emission engines produce low concentrations of soot agglomerates. The absence of these agglomerates to act as sites for adsorption or condensation of volatile materials makes nucleation and high number emissions more likely.
Technical Paper

Diesel Exhaust Aerosol Particle Size Distributions - Comparison of Theory and Experiment

Particle size distributions have been measured in the exhaust of a single cylinder Onan diesel engine using an electrical aerosol analyzer. These measurements give volume mean diameter for the exhaust particles of about 0.1 μm. Other investigators have shown that the particles found in diesel exhaust consist of agglomerates of very small primary particles (about 0.025 μm diameter) and may contain condensed hydrocarbons. A mathematical model has been constructed to determine the particle size distributions which will result from the growth of the primary particles by coagulation. The coagulation equation was solved numerically for an expanding stratified system. The model indicates that the inhomogeneity characteristic of stratified combustion can explain the rapid growth of the primary particles into the larger particles observed in diesel exhaust.
Technical Paper

Detecting Knock in Noisy Spark Ignition Engines

This paper examines three strategies of detecting knock that are less dependent of engine noise. The first strategy uses the exhaust temperature, the second uses a dithering method (systematically advancing and retarding the timing), while the third uses the standard deviation of knock intensity as the indicator of knock intensity. The first strategy proves to be difficult to detect knock since the exhaust temperature is strongly dependent on the combustion efficiency instead of knock intensity. The second strategy uses a conventional accelerometer but discriminates against mechanical noise by subtracting the knock intensity during the retarded part from that of the advanced part of a dither cycle. This approach is found to require averaging the signals over large number of engine cycles and using large dither amplitude. The third strategy uses the Difference of Knock Intensity strategy where two cycle standard deviation is used.
Technical Paper

Combustion of Minimally Processed Coal Liquids in a Diesel Engine

A modified CFR Cetane engine was used to analyze combustion characteristics and emissions of minimally processed coal liquids (MPCLs). To aid in combustion of the coal liquids, the ability to heat the fuel and inlet air was added. The MPCLs are derived from atmospheric distillation of coal liquids. The coal liquids are byproducts of coal gasification of Elkhorn bituminous and North Dakota lignite using the atmospheric, air blown Wellman-Galusha and pressurized, oxygen blown Lurgi gasifiers, respectively. The MPCLs were compared with three reference fuels: diesel No. 2, U12 (21 cetane number) and #-methyl napthalene (0 cetane number). The inlet air was heated from 340 to 535 K and the compression ratio was varied from 13 to 31 to provide sufficient range in temperature and pressure necessary for the combustion of low cetane number fuels. At each operating condition, fuel consumption, cylinder pressure, ignition delay, and emisions were measured.
Technical Paper

A PC-Based Fuel and Ignition Control System Used to Map the 3-D Surfaces of Torque and Emissions Versus Air-Fuel Ratio and Ignition Timing

A system was designed for controlling fuel injection and ignition timing for use on a port fuel injected, gas-fueled engine. Inputs required for the system include manifold absolute pressure, manifold air temperature, a once per revolution crankshaft pulse, a once per cycle camshaft pulse, and a relative encoder pulse train to determine crank angle. A prototype card installed in the computer contains counters and discrete logic which control the timing of ignition and injection events. High current drivers used to control the fuel injector solenoids and coil primary current are optically isolated from the computer by the use of fiber optic cables. The programming is done in QuickBASIC running in real time on a 25 MHz 80486 personal computer. The system was used to control a gas-fueled spark ignition engine at various conditions to map the torque versus air-fuel ratio and ignition timing. Each surface was mapped for a given fuel flow and speed.