Aleš Hribernik

Velocity measurements in a shotblasting machine

Abstract Abrasive shotblasting particles and a high concentration of dust within the closed testing chamber make particle velocity measurement in a shotblasting machine very difficult. The application of non-obstructive optical methods is usually impossible. Robust shields protecting the sensors from abrasion have to be used for contacting velocity measurements and make direct application of capacitive or electrodynamic sensors usually applied in the correlation-based velocity measurements methods not possible. An alternative electronic measurement system has been developed. It has a simple construction and uses low cost elements which can be replaced very quickly and, therefore, no robust shields are necessary. This enables very good mobility and positioning of the sensor along both axis in a cross-section plane of a particle stream. The system has been tested along with a robust mechanical measuring device. The development, operation and application of mechanical and electronic particle velocity measurement system are described in this paper. Experimental results are presented, discussed and both methods are compared.

Determination of the Realistic Turbocharger Efficiency With Pulsating Gas-Flow Compared on a 4-Cylinder Engine

Small single or twin entry radial turbines are mostly used to drive compressors of the turbocharged internal combustion engines. There are two general possibilities to feed the turbine of a four-stroke, 4-cylinder turbocharged Diesel engine: 1) by preserving most of the available exhaust kinetic energy, or 2) by mixing exhaust pulses from all cylinders in one common manifold. In the first case, better utilization of the dynamic pulse energy increases efficiency of the turbine; highly unsteady mass flow of the exhaust gasses, on the other hand, and thus periods of partial exhaust flow admission at the turbine inlet simultaneously reduces this gain in the turbine efficiency. More steady mass-flow of the exhaust gasses is created in the case of the exhaust system 2), however some kinetic energy is lost during the mixing phase in the common exhaust manifold. Calculation of the overall turbocharger and turbine efficiency is normally based on average values of the measured pressures and temperatures. As the result apparent efficiencies are obtained; the more the flow is pulsating, the bigger is the difference between the real and the apparent efficiency. The ratio between these two efficiencies is known as the energy pulsation factor β. It depends generally on the “pulse intensity”-pressure deviation from its mean value, shape of the pressure pulse, number of the individual pulses feeding separate gas turbine inlets, turbocharger, and can be successfully used to determine real efficiency of a turbocharger and to define some working parameters of the engine.A field of β factors for different engine running conditions and for the 4-cylinder engine with 2-cylinder group pulse system (rarely applied), and the commonly applied exhaust system with 4-cylinder group and moderate pressure fluctuation is presented in the paper. Influence of the dynamic exhaust temperatures on the β value is discussed as well.Copyright

Measuring the velocities of particles in a shot-blasting chamber

This paper presents a method for measuring the velocity of a flow of particles accelerated on a shot-blasting wheel and then expanding into space at a wide angle of approximately 45°. The method uses the pulsed nature of the flow characteristic for turbo machinery with a finite number of wheel blades and calculates the velocity from the time shift between the particles hitting two targets at a known distance. This method does not depend on the material properties of the particles; however, a large number of particles is required for a successful measurement. The impacts are detected with a microphone covered by a steel membrane, making the exposed parts cheap and easily replaceable. This makes the method suitable for industrial test-and-development purposes, including the efficiencies of acceleration measurements. A cross-correlation of the signals was used, but the characteristic cycle (one rotation of the wheel) had to be determined beforehand by overlapping and averaging several cycles in order to compensate for the fact that different particles would be hitting the targets.

Non-destructive method for inward leakage detection of a plate evaporator

A new non-destructive method was developed for the detection of refrigerant leakage at an evaporators inflow. Nitrogen and oxygen gas were successively blown through the evaporator. A gas analyser was applied at the outflow of the evaporator and the oxygen concentration measured. It was possible to detect any leakage by investigating the oxygen concentration–time history diagram.

Influence of the Exhaust System Design on Scavenging Characteristic and Emissions of a Four-Cylinder Supercharged Engine

A four-stroke four-cylinder turbocharged engine can be fitted with two different types exhaust system: a simple common manifold fed by all cylinders, or a twin-branch manifold, where two selected cylinders, directed by the firing order, feed two separate turbine entries. In this case good utilization of the exhaust pressure pulse energy can be achieved at higher loads and lower engine speeds, leading to good overall turbocharger efficiency and favorable pressure distribution during the gas-exchange period. Improved engine scavenging capability affects quality and quantity of the fresh charge and consequently influences the exhaust gas emissions. If, in addition, valve overlap period is increased the benefit of this system is still more evident. Common manifold exhaust system shows its advantage through lower pumping losses at higher engine speeds and lower loads. Both systems were optimized and the results of numerical and experimental work are presented in the paper.