Piston Top Research Articles

Effects of a Ring Crevice on Hydrocarbon Emission from Spark Ignition Engines

Abstract Control of the unreacted fuel would reduce total hydrocarbons from engines, therefore it is necessary to understand the mechanism of exhaust hydrocarbons from spark ignition engines. The authors of this paper would like to pay close attention to the effects of a ring crevice. The fuel-air mixture supplied to a spark ignition engine is compressed into the ring crevice in the compression stroke. The unreacted fuel within the crevice is exhausted in the expansion stroke, if the flame cannot enter the inside of the crevice. The purpose of this work is to separate the effects of the ring crevice on hydrocarbon emission from the other effects, so that the authors have proposed an element model for estimating the in-cylinder oxidation of the hydrocarbon from the crevice. To verify propriety of the theoretical model, the authors have also carried out the experiment with the linear crevices, different from a normal ring crevice, mounted on the piston top, and have obtained the agreement of values between ...

Piston ring coatings for high horsepower diesel engines

Thermal-spray-deposited face coatings were developed for a top compression piston ring operating under the high pressures and temperatures of high horsepower diesel engines. Coatings were deposited by plasma spray and high velocity oxygen fuel (HVOF) techniques onto the piston ring faces. The coatings were evaluated by wear and engine tests. Three coatings were deposited by a plasma spray technique: molybdenum/chromium carbide, molybdenum/molybdenum carbide, and chromium oxide. Nickel chromium/chromium carbide powder was deposited by a HVOF technique. On the basis of wear and engine testing, HVOF nickel chromium/chromium carbide, plasma-sprayed chromium oxide and plasma-sprayed molybdenum/chromium carbide were identified to have wear resistances superior to that of today's electroplated chromium and molybdenum carbide coatings. Cylinder liner wear was found to be generally equivalent or lower for the thermal spray coatings when compared with the electroplated chromium.

Piston Ring Thermal Transient Effects on Lubricant Temperatures in Advanced Engines

One class of advanced diesel engines operates with low heat rejection and high operating temperatures; piston-ring / liner lubrication is a major problem for these engines. This study attempts to illustrate the time-dependent thermal environment around the top piston ring and lubricant in these advanced engines. Particular emphasis will be placed on the maximum lubricant temperature. The analysis starts with a standard cycle simulation and a global finite-element analysis of the piston and liner in relative motion. A more detailed finite-element model, which considers variable oil film thickness on the liner, focuses on the top ring and lubricant and uses the groove and liner temperatures generated in the global analysis as boundary conditions. Results for different heat rejection engine configurations are presented. We observe that because of major transient effects, high lubricant temperature is experienced not only at top ring reversal but also down the liner to bottom ring reversal.

The back scattered LDV measurements of swirl flow in an internal combution engine.

The purpose of this paper is to clarify the air motion of swirl flow in a reciprocating engine. The swirl velocities under motoring conditions were measured by a back scattered LDV using a bottom-view research engine. Experiments were conducted with three different combustion chambers having the same compression ratios. The results are as follows: (1) The swirl velocity in the cylinder increases in proportion to the engine speed. (2) The swirl velocity at the compression stroke increases due to the fact that the swirl flow is pushed into the cavity on the piston top. (3) At the compression TDC, the swirl ratio of a deep dish chamber is higher than the ratios of a pancake and a shallow dish chamber.

Room at the piston top contributions of combustion science to engine design

Charles F. Kettering, “Boss Ket,” the founder of the General Motors Research Laboratories, once said: “It's so simple to explain [the automobile engine] by saying, you take a charge of gasoline and air into the cylinder, compress it and ignite it with a spark, and it explodes and pushes the piston down, and that makes your car go … If you stop right there, it is a logical explanation. But what does the spark do? What do you mean by combustion? We don't know why or how the spark sets off that explosion of gas … So I say, quite solemnly, that we haven't the slightest idea what really makes the contraption run. We call the reaction ‘combustion’ because it nicely conceals our lack of knowledge on just what takes place in the engine cylinder. I just don't think we can live in this atmosphere of ignorance about what goes on there when our whole business depends on it” [1].

Thermal boundary layer thickness in the cylinder of a spark-ignition engine

The thicknesses of the thermal boundary layers in the cylinder of a spark-ignition engine were measured throughout the complete operating cycle. The engine used for these experiments was a special visualization engine with a square cross-section ‘cylinder’ and two quartz glass walls. Measurements of thickness were taken at different locations, speeds and loads, from schlieren photographs. The results show that the layers on the cylinder wall reach a maximum thickness of about 2 mm at the end of expansion. On the cylinder head and piston top, the layers are two to three times thicker. Reducing engine speed resulted in thicker layers, while changing load showed no significant effects on thickness. It is shown that on the cylinder wall, the thermal boundary layer thickness depends on thermal diffusivity and the time available for the layer to develop. The growth of this layer was correlated with an expression in the form δ T √( αt) ∞ Re 0.2.

Friction and wear processes in piston rings

It has been recognised that a large part of the top piston ring wear of an ic engine takes place in boundary lubrication around top dead centre (tdc) position. A quantitative assessment of the friction behaviour using actual piston ring and cylinder liner under conditions close to tdc has been made. The factors responsible for wear under these conditions have been identified as surface temperature, peak combustion pressure, total energy on the wearing surfaces and other physical properties of the material under sliding

Experiments on the transmission paths and dynamic behavior of engine structure vibrations. I. Background and static tests

In order to establish a method of estimating the engine structure surface responses, a series of experiments was made on a four-cylinder (bore: 86 mm, stroke: 84 mm), in-line, water-cooled high-speed diesel engine. The results obtained in static conditions are summarized with the necessary background. The propagation behavior of excitation forces in the engine structure, the vibration behavior of the vibration transmission paths, and the transfer functions of the transmission paths were examined in static conditions. The distribution of the damping in the engine structure, the influence of cooling water, the lubrication oil, the oil pressure, and the crank position on the transfer functions were also examined. After the experiments, we found that (a) a different excitation force induces different responses on the engine structure surfaces because of its different transmission paths and their transmission behavior; (b) the forces applied on the cylinder head can be transmitted along the cylinder head bolts, and the engine structure can be excited by this force just as strongly as by the identical force applied on the piston top; and (c) most of the damping in the engine structure is induced by the oil film existing around the main moving parts such as the pistons, the connecting rods, and the crankshaft.

Cell design for pressure to 25 kbar

A cell design is presented for experiments with hydrostatic pressures up to 25 kbar. The pressure-transmitting medium around the sample is candle wax, which is sealed in the cavity with molybdenum disulfide impregnated nylon and aluminum disks. This approach showed no detectable leakage to 25 kbar. Internal cavity pressure is computed from measurements of the applied load on the top piston, the transmitted load to the lower piston, and the frictional forces transmitted by the seals into the pressure vessel and the cell body. Internal pressure thus measured and phase-transition pressure data from RbCl and KBr are all within 9% of each other for the pressure range 3-25 kbar.

An experimental research on the vibration transmission paths and their dynamic behavior of engine structure vibration

The vibration transmission paths of gas force, the most dominant excitation force in diesel engine, were identified by exciting the piston top and cylinder head surface and measuring the acceleration response at piston, connecting rod, crankshaft, main bearing caps, and cylinderblock surface under static condition. A four-cylinder in-line high speed diesel engine was used for the test. The transfer functions for the paths were also measured in examining the fluence of crank angle, coolant, lubricant, and journal bearing pressure. The vibration behavior of the engine structure was examined by changing the assembling conditions stepwisely. In order to examine the dynamic behavior of the engine structure vibration, test was also carried on under motoring condition, and the structure responses due to gas force, piston slap, and valve seating impact and so on could be identified separately.

Paper 11: The Use of a Motored Engine to Study Piston-Ring Wear and Engine Friction

The paper describes a study of the conditions which lead to mechanical, or attritive, wear of a top piston- ring. A motored single-cylinder engine was used, and piston-ring wear measurements were made using a radioactive tracer technique. By connecting the inlet and exhaust ports together and pressurizing the system with nitrogen, peak cylinder pressures could be matched to those in a firing engine and corrosive wear minimized. Ring belt oil viscosities were matched to those in service either by using low-viscosity oils or by restricting the cooling. Wear was caused, under steady-speed conditions, by increasing the peak pressure or the cylinder-liner temperature. However, even under the most severe conditions, the wear rate eventually became negligible with the liner surface becoming highly polished. Under comparable conditions in a fired engine a steady rate of wear was observed. It was found that large variations in piston-ring wear could occur without any detectable change in the motoring torque. Torque was linearly related to the peak cylinder pressure. The component of the motoring torque attributable to the piston assembly friction varied as the square root of the ring belt oil viscosity. The results suggest that, in a fired engine, hydrodynamic lubrication should be attainable throughout the stroke if roughening of the surfaces by the effects of combustion products could be prevented.

Improved lubricating system for BEDFORDS

Modifications to the latest Bedford trucks and passenger vehicles include some important improvements to the lubricating and ventilating systems. These improvements include the fitting of chromium plated top piston rings and slotted scraper rings, improved finish to cylinder walls, fitting of copper‐lead bearings, efficient air filtration, incorporation of a positive system of crankcase ventilation, and the fitting of a larger oil filter. These modifications, together with the use of an induction‐hardened crankshaft and a larger Zenith carburettor, are claimed to produce a higher power output resulting in higher average speeds and improved hill‐climbing with no increased fuel consumption.