By Kristen Purcell and Lee Rainie Summary of Findings The internet and cell phones have infiltrated every cranny of American workplaces, and digital technology has transformed vast numbers of American jobs.
TURBOCHARGER BASICS Since the power a piston engine can produce is directly dependent upon the mass of air it can ingest, the purpose of forced induction turbo-supercharging and supercharging is to increase the inlet manifold Technology in the work force and density so as to make the cylinders ingest a greater mass of air during each intake stroke.
A supercharger is an air compressor driven directly by the engine crankshaft, and as such, consumes some of the power produced by the combustion of fuel, thereby increasing BSFC and engine wear for a given amount of produced power. A turbocharger consists of a single-stage radial-flow "centrifugal" compressor air pumpas shown on the left side of Figure 1 which, instead of being driven directly by the crankshaft, is driven by a single-stage radial-flow exhaust turbine as shown on the right side of Figure 1.
The turbine extracts wasted kinetic and thermal energy from the high-temperature exhaust gas flow and produces the power to drive the compressor, at the cost of a slight increase in pumping losses.
Figure 1 Borg-Warner Turbocharger with Variable Geometry Turbine Turbochargers are becoming ever more widely used in racing, as motorsport increasingly embraces energy efficiency.
It is expected that turbos will soon ? There is a considerable amount of development work currently being done on turbochargers, which is being motivated primarily by the following road-vehicle requirements: These days, compression-ignition CI road car engines are invariably turbocharged and this relatively-fast developing technology is operating at ever-rising BMEPs, which means higher combustion temperatures and the resulting increases in NOx emissions.
Although these motivators are coming from the production-vehicle end of the spectrum, the resulting technology is or will soon be available for application into motorsports.
At present, competition CI engines are not required to reduce NOx emissions but that will surely develop as political correctness further invades motorsportsso the increased compressor efficiencies, flowrates and map widths can be used to provide greater intake density at the mandated manifold absolute pressure MAP limits.
The increased compressor efficiencies, flowrates, and map widths developed for CI technology will certainly benefit competition SI engines in the same way. The compressor RPM lines show, for the stated compressor speed in thousands of RPMthe pressure ratio delivered as a function of airflow.
It defines, for each pressure ratio, the minimum airflow at which the compressor can operate.
Airflows to the left of the surge line cause the air to separate from the blades and experience a "stall" phenomenon similar to the stall of an aircraft wing.
This is an area of instability in which the airflow moves in a chaotic manner, causing snapping and popping, and potential blade damage.
Surge can occur with a downstream-throttled installation when the throttle is suddenly closed if there is no blowoff valve or other device to vent airflow. The dotted line up the center of the map is the peak efficiency operating line: Note from the map that, for a given compressor RPM, the available pressure ratio reaches a point where it begins to drop quickly as airflow increases.
This effect is less severe at lower rotor RPM, but with higher rotor RPM therefore higher available pressure ratiothe pressure ratio drops dramatically with a slight increase in airflow.
This phenomenon is known as "choke". The choke condition is defined differently by different manufacturers: Compressor efficiency is an important concept to understand with regard to forced induction. At standard atmospheric conditions Compressing that mass of air into a smaller volume increases the pressure, the temperature and the density.
Here is an example. That would result in a manifold pressure, temperature and density of Please note that it is beyond the scope of this article to explain the details of these example calculations. Be assured they are relatively straightforward, and are presented in several excellent textbooks, including EPI Reference Library volumes 5: The compressor side of a turbocharger faces significant thermal, stress and fatigue challenges.
In most applications, the compressor is ingesting air at slightly more than ambient temperature, but the temperature rise across the compressor can be substantial as explained in Turbocharger Basics at the beginning of this article.
With ambient inlet air and a 4: However, the low temperature of the inlet air plus the fact that most of the temperature rise occurs in the diffuser, where velocity is exchanged for pressure, typically keeps the operating temperature of the compressor wheel well below the compressor discharge temperature.
A compressor wheel, often operating at overRPM, is subjected to high centrifugal loads. High pressure ratios apply bending loads to the blades. Cycling between pressure ratios of 1.
Surviving these cyclic loads at elevated temperatures can be a problem. Currently, most production compressor wheels are aluminium investment castings, and a very popular material is the permanent-mold alloy T Wheels cast from the very-high strength alloy T7, using a permanent mold process, have also been successful in compressor applications, but this alloy is more difficult to pour successfully than is The compressor wheels in most performance applications, including the Audi and Peugeot Le Mans turbodiesels, are five-axis CNC machined from forged series aluminium billet.
According to Turbonetics, that procedure provides wheels with optimal properties and accuracy, frees them from the costs involved in permanent mold tooling, and gives them a large measure of flexibility to experiment and modify existing designs. However, much of the current direction in compressor improvement is being driven by the pressure ratio and flow requirements of CI engines for road vehicles, operating at high boost levels and high levels of EGR to reduce emissions of NOx.
Wide-map compressors with pressure ratios of 4:NIST promotes U.S. innovation and industrial competitiveness by advancing measurement science, standards, and technology in ways that enhance economic security and improve our quality of life.
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