Side Of Combustion Chamber Research Articles

Thermo-acoustic Instabilities in the PRECCINSTA Combustor Investigated Using a Compressible LES-pdf Approach

This work predicts the evolution of self-excited thermo-acoustic instabilities in a gas turbine model combustor using large eddy simulation. The applied flow solver is fully compressible and comprises a transported sub-grid probability density function approach in conjunction with the Eulerian stochastic fields method. An unstable operating condition in the PRECCINSTA test case—known to exhibit strong flame oscillations driven by thermo-acoustic instabilities—is the chosen target configuration. Good results are obtained in a comparison of time-averaged flow statistics against available measurement data. The flame’s self-excited oscillatory behaviour is successfully captured without any external forcing. Power spectral density analysis of the oscillation reveals a dominant thermo-acoustic mode at a frequency of 300 Hz; providing remarkable agreement with previous experimental observations. Moreover, the predicted limit-cycle amplitude is found to closely match its respective measured value obtained from experiments with rigid metal combustion chamber side walls. Finally, a phase-resolved study of the oscillation cycle is carried out leading to a detailed description of the physical mechanisms that sustain the closed feedback loop.

Vortex nozzle interaction in solid rocket motors: A scaling law for upstream acoustic response.

In solid rocket motors, vortex nozzle interactions can be a source of large-amplitude pressure pulsations. Using a two-dimensional frictionless flow model, a scaling law is deduced, which describes the magnitude of a pressure pulsation as being proportional to the product of the dynamic pressure of the upstream main flow and of vortex circulation. The scaling law was found to be valid for both an integrated nozzle with surrounding cavity and a nozzle geometry without surrounding cavity that forms a right angle with the combustion chamber side wall. Deviations from the scaling law only occur when unrealistically strong circulations are considered.

The swirl ratio influence on combustion process and heat transfer in the opposed piston compression-ignition engine

In order to maximise engine heat efficiency an engines charge flow must be properly designed -especially its swirl and tumble ratio. A two-stroke compression-ignition opposed piston engine reacts to engine swirl differently compared to a standard automotive engine with axially symmetric combustion chamber. In order to facilitate direct fuel injection, high-pressure injectors must be positioned from the side of combustion chamber. Depending on the combustion chamber geometry the swirling gases impact greatly how the injection stream is formed. If the deformation is too high the high temperature combustion gases can hit the piston surface or get into gaps between the pistons. This greatly affects the heat lost to the pistons and raises their local temperature. More atomised injection stream is more prone to swirling gas flow due to its reduced droplet size and momentum. The paper presents simulation results and analyses for different intake process induced swirl ratios and different types of combustion chambers in an experimental aviation opposed piston engine.

Thermal Protection of Internal Combustion Engines Pistons

The research aiming to improve the reliability and durability of internal combustion engines (ICE) has traditionally been relevant. Today, the use of ceramic materials and coatings in engine manufacturing is an increasingly frequent research subject. The most promising method to form such coatings on aluminum-alloy pistons is microarc oxidation (MAO). The goal of this research is to study the efficiency of thermal protection provided by a MAO layer on the piston head experimentally. To determine the optimum coating thickness, we have simulated the thermal state of the piston using ANSYS Multiphysics. Then we carried out motor tests of the pistons using the single-cylinder unit of a four-cylinder two-stroke engine. The coating was applied to the surface of the piston head on the combustion chamber side. We tested the pistons with MAO coating thicknesses of 76 and 106 μm. The piston temperature was measured on the piston head surface on the crankcase side using temperature indicators. The tests were carried out under excess air factor α=0.95 at the full-load curve. As a result, we have elicited the positive effect of MAO coating applied to the piston head. Per calculation and test results, such coating reduced the temperature of the piston by 45...78 °C. The thickness of the MAO layer was not found to have any significant impact on the thermal state of the piston. The research results are applicable in engine manufacturing when designing new engines or upgrading the existing engines to make them more reliable.

Design and Simulation Optimization of Casting Process for Aluminum Alloy Engine Cylinder Head

The liquid metal filling and solidification process of aluminum engine cylinder head in different gating system during casting process was simulated by casting simulation software MAGMAsoft. The simulation results showed that the best pouring process contains the bottom note type casting and the placement of combustion chamber side, so that we could obtain a simple modeling process, and significantly shorten the trial production cycle, as well as the trial cost of the piston, and improve the quality of the cylinder head.

Regeneratively cooled scramjet heat transfer calculation and comparison with experimental data

Regeneratively cooled scramjet heat transfer calculation method was developed using three-dimensional calculation for engine solid wall heat conduction. The scramjet thermal environment was determined by engine heat flux measurement and the engine three-dimensional combustion flow calculations. Different heat transfer relationships in the laminar, transition and turbulence fuel flow regions were applied. The cooling fuel flow distribution data inside combustion chamber side panel were obtained by three-dimensional fuel cooling flow calculation. The results of a light weight regeneratively cooled combustion chamber heat transfer tests were adopted to verify the calculation method. The comparisons showed good agreement, indicating that the calculation method is applicable.

Nimonic compound exhaust valve spindles for diesel engines via hot isostatic pressing

Until the present time the materials used for exhaust valve spindles for diesel engines have comprised a main body of heat resistant austenite steel with a Stellite layer covering the seat area. Recently, to satisfy increasing demands for higher efficiency of engines, a forged Nimonic 80 exhaust valve spindle has been developed. This valve spindle has higher strength and hot corrosion resistance than conventional austenite steel valves. This paper introduces a compound type Nimonic 80A-austenite steel valve spindle produced via hot isostatic pressing. Nimonic 80A powder metal is consolidated and diffusion bonded to an austenite spindle body. The seat area and the total combustion chamber side of the spindle are clad using Nimonic 80A. The compound valve spindle produced via hot isostatic pressing has the same performance as a forged Nimonic 80A spindle and in addition it has improved repair weldability and hot corrosion resistance compared with the forged Nimonic 80A spindle valve. Because less of the expensive Nimonic 80A material is used, there is an added advantage in that the cost of the valve would be cheaper. Successful engine test results are also described

Piston Ring Deposits When Using Vegetable Oil as a Fuel

Abstract This paper documents the presence of piston ring deposits responsible for sticking piston rings in the diesel engine when using a vegetable oil-diesel fuel blend. It was found that piston ring immobilization is caused by carbon buildup on the combustion chamber side of the rings and in the annular space behind the rings. The carbon buildup is postulated to be the result of a polymerization growth process on preferred metallic surfaces. Most of the growth takes place on the relatively more stationary piston groove rather than on the ring. Carbon buildup preference was found for aluminum rather than cast iron at a common junction of the two metals. Possible solutions to these major problems are summarized.