Page 18 - PCA Metro NY Region POST | 2019-August-eMag
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Forced Induction and Electric Vehicles
It seems that all the talk today is about electric vehicles; Ford is partnering with VW, the Tesla Model 3 is finally being produced in large numbers, Porsche’s electric Taycan is expected this year, and more and more EVs are be- ing purchased. But the internal combustion
engine hasn’t given up yet and in fact, there is a great deal of innovation underway, specifically in the area of forced induction.
Forced induction
“Forced Induction” is the term to describe a means of getting more air into an engine’s cyl- inders than would enter them normally by the suction of downward motion of the pistons. This ordinary method of an engine’s breathing is often called ‘normal aspiration’. Porsche 944 lovers are familiar with references to 944 NA vehicles, referring to non-turbo Normally Aspirated cars. There are two types of forced induction: Turbo- charged and Supercharged.
Turbocharged engines route the hot (i.e., energy- laden) exhaust gasses past a turbine wheel on their way to the tailpipe. This causes the wheel to spin rapidly. This wheel is attached to a shaft on which another turbine wheel in the intake mani- fold, called the impeller wheel, is placed. The spinning of the impeller adds additional pressure to the air in the intake stream and consequently forces a greater volume of air into the cylinders than would occur if the same engine did not have these turbo wheels. A greater volume of air in the cylinders (and suitable extra fuel) increases the amount of force created by each spark explo-
sion. The beauty of the turbo system is that the power needed to drive the impeller wheel comes from exhaust gasses which in a normally aspi- rated engine are completely wasted since they are directly routed out the exhaust pipes. The downside with turbos is that at low revs there
is insufficient energy in the exhaust to spin the impeller with enough force to create much addi- tional pressure, so there isn’t much ‘turbo’ effect until the revs have climbed higher. This causes the unpleasant ‘turbo lag’ phenomenon. Superchargers also increase the pressure of the air in the intake stream, but they do it by driving the impeller wheel directly off the engine by use of a belt, shaft, or gears connected to a spinning component of the engine. The beauty of the su- percharging system is that substantial pressure is available even at low revs since the speed of the impeller wheel is directly proportional to the engine revs, unlike with turbos. Supercharged engines do not suffer from anything like turbo lag. The downside with superchargers is that they sap a great deal of the engine’s power to drive the impeller, unlike the turbo which is driv- en by the otherwise completely wasted exhaust gasses.
Both these forced induction systems have a long history. Gottfried Daimler of Mercedes fame got a patent for a supercharging system in 1885 and there were turbo engines on some French fighter planes as far back as World War 1. All the pow- ers used forced induction engines in World War 2 aircraft. Forced induction is particularly useful in piston-engine aircraft because air density de- creases greatly at higher altitudes, which directly reduces the power potential and thus the maxi- mum speed and altitude possible. The turbo or supercharged aircraft engine makes up for this loss of intake air pressure.
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Track Ramblings
FRED PACK - DE INSTRUCTOR
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METRO NY REGION PCA * PORSCHE POST AUGUST 2019





















































































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