Search Results

A method for determining the flame contour based on the flame arrival time at the fiber optic (FO) spark plug and at the head gasket ionization probe (IP) locations has been developed. The experimental data were generated in a single-cylinder Ricardo Hydra spark-ignition engine. The head gasket IP, constructed from a double-sided copper-clad circuit board, detects the flame arrival time at eight equally spaced locations at the top of the cylinder liner. Three other IP's were also installed in the cylinder head to provide additional intermediate data on flame location and arrival time. The FO spark plug consists of a standard spark plug with eight symmetrically spaced optical fibers located in the ground casing of the plug. The cylinder pressure was recorded simultaneously with the eleven IP signals and the eight optical signals using a high-speed PC-based data acquisition system.

The effect of engine operating parameters (speed, spark timing, and fuel-air equivalence ratio [Φ]) on hydrocarbon (HC) oxidation within the cylinder and exhaust system is examined using propane or isooctane fuel. Quench gas (CO2) is introduced at two locations in the exhaust system (exhaust valve or port exit) to stop the oxidation process. Increasing the speed from 1500 to 2500 RPM at MBT spark timing decreases the total, cylinder-exit HC emissions by ∼50% while oxidation in the exhaust system remains at 40% for both fuels. For propane fuel at 1500 rpm, increasing Φ from 0.9 (fuel lean) to 1.1 (fuel rich) reduces oxidation in the exhaust system from 42% to 26%; at 2500 RPM, exhaust system oxidation decreases from 40% to approximately 0% for Φ = 0.9 and 1.1, respectively. Retarded spark increases oxidation in the cylinder and exhaust system for both fuels. Decreases in total HC emissions are accompanied by increased olefinic content and atmospheric reactivity.

The extent of oxidation of hydrocarbons desorbing from the oil layer has been measured directly in a hydrogen-fueled, spark-ignited engine in which the lubricant oil was doped with a single component hydrocarbon. The amount of hydrocarbon desorbed and oxidized could be measured simultaneously as the dopant was only source of carbon-containing species. The fraction oxidized was strongly dependent on engine load, hydrogen fuel-air ratio and dopant chemical reactivity, but only modestly dependent on spark timing and nitrogen dilution levels below 20 percent. Fast FID measurements at the cylinder exit showed that the surviving hydrocarbons emerge late in the exhaust stroke.

This paper contains both theorems and correlations based on the idea that there is a uniform metric for measuring the complexity of mechanical parts. The metric proposed is the logarithm of dimension divided by tolerance. The theorems prove that, on the average, for a given manufacturing process, the time to fabricate is simply proportional to this metric. We show corrleations for manual turning (machine lathe process), manual milling (machine milling process), and the lay-up of composite stringers. In each case the accuracy of the time estimate is as good as that of traditional cost estimation methods, but the effort is much less. The coefficient for composite lay-up compares well to that obtained from basic physiological data (Fitts Law).

Enhanced information management techniques made available through emerging Information Technology platforms hold a promise of providing significant improvements in both the effectiveness and efficiency of developing complex products. Determining actual management implementations that deliver on this promise has often proven elusive. Work in conjunction with the Lean Aircraft Initiative at MIT has revealed a straight forward use of Information Technology that portends significant cost reductions. By integrating previously separate types of data involved in the process of product development, engineers and designers can make decisions that will significantly reduce ultimate costs. Since the results presented are not specific to particular technologies or manufacturing processes, the conclusions are broadly applicable.

A complete one-dimensional mixed lubrication model has been developed to predict oil film thickness and friction of the piston ring-pack. An average flow model and a roughness contact model are used to consider the effects of surface roughness on both hydrodynamic and boundary lubrication. Effects of shear-thinning and liner temperature on lubricant viscosity are included. An inlet condition is applied by considering the unsteady wetting location at the leading edge of the ring. A ‘film non-separation’ exit condition is proposed to replace Reynolds exit condition when the oil squeezing becomes dominant. Three lubrication modes are considered in the model, namely, pure hydrodynamic, mixed, and pure boundary lubrication. All of these considerations are crucial for studying the oil transport, asperity contact, and friction especially in the top dead center (TDC) region where the oil control ring cannot reach.

A Lagrangian random vortex-boundary element method has been developed for the simulation of unsteady incompressible flow inside three-dimensional domains with time-dependent boundaries, similar to IC engines. The solution method is entirely grid-free in the fluid domain and eliminates the difficult task of volumetric meshing of the complex engine geometry. Furthermore, due to the Lagrangian evaluation of the convective processes, numerical viscosity is virtually removed; thus permitting the direct simulation of flow at high Reynolds numbers. In this paper, a brief description of the numerical methodology is given, followed by an example of induction flow in an off-centered port-cylinder assembly with a harmonically driven piston and a valve seat situated directly below the port. The predicted flow is shown to resemble the flow visualization results of a laboratory experiment, despite the crude approximation used to represent the geometry.

This paper describes the use of a modified quasi-dimensional spark-ignition engine simulation code to predict the extent of cycle-to-cycle variations in combustion. The modifications primarily relate to the combustion model and include the following: 1. A flame kernel model was developed and implemented to avoid choosing the initial flame size and temperature arbitrarily. 2. Instead of the usual assumption of the flame being spherical, ellipsoidal flame shapes are permitted in the model when the gas velocity in the vicinity of the spark plug during kernel development is high. Changes in flame shape influence the flame front area and the interaction of the enflamed volume with the combustion chamber walls. 3. The flame center shifts due to convection by the gas flow in the cylinder. This influences the flame front area through the interaction between the enflamed volume and the combustion chamber walls. 4. Turbulence intensity is not uniform in cylinder, and varies cycle-to-cycle.

The occurrence of liquid fuel in the cylinder of automotive internal combustion engines is believed to be an important source of exhaust hydrocarbon (HC) emissions, especially during the warm-up process following an engine start up. In this study a Phase Doppler Particle Analyzer (PDPA) has been used in a transparent flow visualization combustion engine in order to investigate the phenomena which govern the transport of liquid fuel into the cylinder during a simulated engine start up process. Using indolene fuel, the engine was started up from room temperature and run for 90 sec on each start up simulation. The size and velocity of the liquid fuel droplets entering the cylinder were measured as a function of time and crank angle position during these start up processes. The square-piston transparent engine used gave full optical access to the cylinder head region, so that these droplet characteristics could be measured in the immediate vicinity of the intake valve.

The adoption of turbine engines for automotive power plants has been hampered by the high cost, high leakage and high wear rate of present designs of ceramic-matrix regenerators. Proposals are made and analyzed here for design directions to achieve substantial improvements in all three areas. These include lower-cost extruded and pressed matrices; and clamping seals coupled with incremental movement of the rotary-regenerator matrix.

Human explorers of planetary surfaces would benefit greatly from a spacesuit design that facilitates locomotion. To aid in the development of such an extravehicular activity suit, a design effort incorporating the concept of mechanical counter pressure (MCP) was undertaken. Three-dimensional laser scanning of the human body was used to identify the main effects of knee flexion angle on the size and shape of the leg. This laser scanning quantified the changes in shape that must be supported by an MCP garment and the tension that must be developed to produce even MCP. Evaluation of a hybrid-MCP concept using inextensible materials demonstrated strong agreement between experimental data and a mathematical model with rigid cylinder geometry. Testing of a form-fitting garment on the right lower leg of a subject demonstrated successful pressure production. Further research is required to evaluate how evenly pressure can be distributed using the hybrid-MCP concept.

Frictional losses in the piston ring-pack of an engine account for approximately half of the total frictional losses within the power cylinder of an engine. Three-dimensional honing groove texture was modeled, and its effect on piston ring-pack friction and engine brake thermal efficiency was investigated. Adverse effects on engine oil consumption and durability were also considered. Although many non-conventional cylinder liner finishes are now being developed to reduce friction and oil consumption, the effects of surface finish on ring-pack performance is not well understood. A rough surface flow simulation program was developed to calculate flow and stress factors that adjust the solution of the Reynolds equation for the effects of surface roughness as has been done in the literature. Rough surface contact between the ring and liner was modeled using a previously published methodology for asperity contact pressure estimation between rough surfaces.

The knocking characteristics of several fuels are studied using a single cylinder test engine with variations in key engine operating parameters. Compression ratio, spark advance, fuel equivalence ratio, exhaust gas recirculation, engine speed, charge inlet pressure and charge inlet temperature were varied to yield a range of engine cylinder pressure-temperature histories as the base for this study. The fuels studied include three reference fuels containing isooctane and heptane with isooctane volume percents of 80, 90 and 100. Two wide boiling range gasolines were also studied. A number of empirical relationships for autoignition times of isooctane and heptane blends are employed in conjunction with the experimentally obtained pressure-temperature histories to predict onset of knock. The accuracies of the predictions with respect to the experimentally determined knock points are discussed.

A time resolved study of the unhurned hydrocarbons in the cylinder of a spark ignition engine has been made. A fast acting needle value was used to sample the gas near the cylinder wall opposite the spark plug. The volume sampled was measured by water displacement and the total hydrocarbon mole fraction was measured with a flame ionization detector. Measurements were made as a function of crank angle over the entire engine cycle for a range of equivalence ratios, inlet pressures, spark advances, inlet temperatures, and EGR fractions. Average hydrocarbon concentrations in the exhaust were also measured. Two possible sources of post combustion hydrocarbon in the cylinder were considered: thin wall quench layers and fine crevices into which a flame cannot propagate. The results suggest that crevices were the source of the hydrocarbon. Models for predicting hydrocarbon from both quench layers and crevices were developed and are presented.

THIS paper reports the latest investigation of the relative merits of loop scavenging versus through scavenging. The authors hope that the conditions of the work permitted an objective evaluation of the two types of engines. The results of the study may be summarized as follows: 1. With symmetrical timing, neither cylinder shows significant advantage in trapping efficiency. 2. With symmetrical timing, the best ratio of exhaust-port to inlet-port effective area seems to be about 0.6. 3. Unsymmetrical timing is an effective method of improving trapping efficiency. 4. The value of net indicated fuel economy shows no significant difference between the two cylinders. The authors point out that because the areas were equal it is unlikely that the optimum port design of each type was used in comparing the cylinders. If optimum porting had been used, the two types might have shown more difference.

The direct injection spark-ignition engine is the only internal combustion engine with the potential to equal the efficiency of the diesel and to tolerate a wide range of fuel types and fuel qualities without deterioration of performance. However, this engine has low combustion efficiency and excessive hydrocarbon emissions when operating at light load. In this paper, potential sources of hydrocarbon emissions during light load operation are postulated and analyzed. The placement of fuel away from the primary combustion process in conjunction with a lack of secondary burnup are isolated as important hydrocarbon emissions mechanisms. Analyses show that increasing cylinder gas temperatures can improve secondary burnup of fuel which would reduce hydrocarbon emissions. Practical means to achieve this include higher compression ratio and use of ceramic parts in the combustion chamber.

Zinc coating integrity, composition, thickness, roughness, and the presence of Fe-Zn intermetallics are being investigated with regard to the mechanisms of weld nugget formation. This information is being used in conjunction with the optimization of the weld process parameters; such as upsloping, down-sloping, preheating, postheating, and double pulsing, to provide the widest range of acceptable welding conditions. Dynamic inspection monitoring of the welding current, voltage, force, and nugget displacement is being used to follow the progression of nugget formation and to assist in the evaluation of optimum process and material characteristics. It has been found that hot-dipped galvanized materials with coatings which have a very thin Fe-Zn alloy layer, have a wider range of acceptable welding conditions than the commercial galvannealed products, which have a fully alloyed Fe-Zn coating.

The fracture of pressurized graphite/epoxy cylinders was investigated and their damage tolerance assessed. The cylinders were 610 mm (24 in) long and 305 mm (12 in) in diameter and were fabricated from Hercules A370-5H/3501-6 prepreg cloth in 4-ply configurations: (0,45)s and (45,0)s. The cylinders were slit in the longitudinal direction and the critical flaw sizes for three pressure levels were determined. Experiments on coupons of similar construction loaded in tension were previously conducted. The critical flaw sizes for the cylinders were well predicted from the flat coupon data corrected for the effects of curvature. In addition, circumferentially-wrapped unidirectional plies of Herecules AS1/3501-6 tape of various stacking sequences were used as selective reinforcement on several (0,45)s cylinders. There reinforcing plies did change the path of damage but did not prevent catastrophic failure.

An aerodynamic model of the entrainment of the head wall quench layer during blowdown and exhaust of an internal combustion engine has been developed. The model may be used to calculate the time resolved concentration and mass flowrate of hydrocarbons (HC) in the exhaust, from a knowledge of engine geometry and operating conditions. It predicts that the area As from which HC are swept will be proportional to the cube root of the ratio of the quench layer thickness δq to the thickness of the viscous boundary layer δv. Since the mass of HC emitted is proportional to the product of the HC density ρHC, the area As and the thickness δq, the HC emissions will be proportional to the product ρHC δq4/3 and this is the most important factor determining the emissions.

THE indicated output of a 2-stroke engine is primarily dependent upon the success with which the products of combustion are driven from the cylinder and are replaced by fresh air or mixture during the scavenging period. Such replacement must, of course, be accomplished with a minimum of blower power. This paper deals with various aspects of 2-stroke research conducted at M.I.T. during the past 10 years. Among the subjects discussed are the methods used in the prediction and measurement of scavenging efficiency, and the effect of engine design and operating variables on the scavenging blower requirements as reflected by the scavenging ratio.