Performance of a Supercharged Passenger-Car 280041
A STUDY of the effect of supercharging on the performance of the engines of passenger-cars showed that the power increase varied from 35 per cent at 1000 r.p.m. to 59 per cent at 3000 r.p.m., with a maximum supercharging pressure of only 6.5 lb. per sq. in. In acceleration tests made at the General Motors Proving Ground of two cars of similar model, one equipped with a supercharged engine and the other with a high-compression engine, the supercharged car accelerated from 5 to 25 m.p.h. in 5 sec.; the unsupercharged car, in 10 sec. From 15 to 50 m.p.h. the supercharged car accelerated in 12.7 sec.; the unsupercharged car, in 21.0 sec. On an 11-per cent grade up which the cars were started at 10 m.p.h., the speed of the supercharged car was 40 m.p.h. at the top; that of the unsupercharged car was 18 m.p.h. These and other results of the tests are portrayed by curves.
Only the turbo or centrifugal type of supercharger would be successful on passenger-cars, according to one discusser, because some device is needed to break up the fuel rather than to supercharge the engine. Automobiles could run faster if they could get more fuel, and a stock-car engine equipped with a supercharger should develop 25 per cent more power than if unsupercharged. A two-cycle engine equipped with a supercharger will develop, at low throttle, about three times as much horsepower per pound of fuel as a conventional four-cycle engine.
Superchargers on airplane engines operate under ideal conditions, according to another speaker, because the density of the air at great altitudes is less than that at sea-level and the temperature is lower. The turbo type seems best for airplanes because the kinetic energy of the exhaust gases can be utilized, but it is difficult to find a suitable material for constructing the turbine buckets, which operate in gases of very high temperature. To obtain the most satisfactory operation, the engine must be designed to meet the requirements of the supercharger.
A centrifugal supercharger having a low gear-ratio maintains the mean effective pressure of the engine constant independently of the engine speed, points out another member, who states that a water-cooled engine rated nominally at 800 hp. is being designed which will develop 1000 hp., it is hoped, when the mean effective pressure is maintained constant at high speeds. The possibility of reducing the weight of aircraft engines by using a two-stroke cycle and supercharging is being studied.
The advantages and disadvantages of suction-type and pressure-type superchargers are discussed, and some research work is mentioned that showed that the use of the centrifugal-type supercharger on a passenger-car engine increased the horsepower 18 or 20 per cent at 3000 r.p.m. The demand of the public for continually increasing the power of cars has caused too large and too heavy engines to be used, it is said, and superchargers must eventually be adopted.
One investigator terms the supercharger a pressure-restorer, as its function is to maintain the inlet pressure.