Boosted Turbocharging in Gasoline Engines and HEVs

by Jeremy Horne, Ph.D.

Background
Whenever I think of turbocharging one of the first things comes to mind are super powered engines that can pass anything on the road except a gas pump. Back in middle of the last century juveniles would give that added boost of power by injecting ambient air into the intake manifold, thus making combustion more efficient. Then, too, they didn’t have to worry so much about fuel economy, as the price of regular gasoline was only about 25 U.S. cents. Most of the sports cars that started to come into the U.S. about that time were more about style and speed. It was not until the early seventies that people saw the price rise to 50 cents and then to a dollar by 1980. Still popular, however, were the large American cars that would be lucky to get 15 to 18 miles per gallon, 12-16 being common. Now we are hearing more about turbocharging, and it wouldn’t make much sense to associate this with speed, as modern engines can do what a turbocharged one could do fifty years ago. With a greater concern over petroleum supplies, especially with the recent events in the Middle East, attention is paid primarily to extending the fuel economy of current vehicles and limiting pollution. It is clear that turbocharging is one way of doing this. On another front, hybrid electric vehicles (HEV) offer a way of cutting down on fuel consumption by relying on power plants to provide energy to charge vehicle batteries. However, the problem here is that ultimately, there must be renewable energy sources to overcome the central problem of diminishing petroleum supplies.

We look at what a turbocharger does and then examine what a modification of it – boosting – would look like to provide power with increased fuel economy. We also visit timing. Afterwards, we will consider how these are coupled with HEV technology to produce better fuel economy.

Construction of a turbocharger
There are two types of turbochargers (“turbo”, for short) – ambient air intake, and exhaust gas recirculation. The first takes in surrounding air, compresses it, and then injects it into the intake manifold ultimately to mix with the gasoline in the automobile’s compression chamber.

 

 

 

 

 

 

 

 

Typical turbocharger for fuel injected engine [1]

The second type of turbocharger is powered through its turbine by the engine’s exhaust. This design recirculates the exhaust gasses back into the intake manifold, atomizing the fuel even more, which gives the added power and fuel efficiency. Normally, not all the fuel is burned because it does not remain in the combustion chamber long enough.

There are several types of turbos, the simplest being a single one. The twin or parallel turbo system consists of two turbos, one for each half of the engine, that being a V-6 or V-8. Using two of these reduces what is called “turbo lag”, the time for the turbo to wind up to the speed required to start sending compressed air to the manifold or cylinders, thus giving the boost. A sequential turbo system uses one smaller turbo for lower revolutions per minute (RPM) and a larger for higher RPMs. Larger turbos are the quads, used on much larger engines, such as v-12s or v-16.

While a turbocharger can boost engine power, it also causes more stress on the engine, thus requiring more oil changes and compensation for heat increase. If there is too much turbocharging, there can be engine failure. Remember, the factory engine was designed for certain stress tolerances, and an aftermarket turbocharger has a potential for causing damage. This being said, the factory installed turbochargers are designed to manage the engine stress issues. It is the after-market (non-original equipment manufactured products installed outside the factory) turbochargers that cause problems.

Interested in reading more about turbocharging? Find more useful content here!