GM Inside News Forum banner
1 - 8 of 8 Posts

·
Moderator
Joined
·
543 Posts
Discussion Starter · #1 ·

Weight is the mortal enemy of performance and efficiency. One of the most effective ways of increasing a vehicle’s fuel economy and improving its driving dynamics is to cut unnecessary mass. Every component is fair game for optimization, including turbochargers.

You’re probably thinking there’s not a lot of weight that can be removed from one of these blowers, after all they’re not that large to begin with. Challenging convention, engineers at supplier company Continental have managed to produce a turbo that’s nearly 30 percent lighter.

The unit they developed features an aluminum turbine housing instead of one made from heavier iron or steel. This lightweight metal might not seem capable of withstanding the intense heat of vehicle exhaust and if the turbo were built in a conventional manner it probably wouldn’t.

Continental’s major innovation with this blower is that the housing is double-walled and features a generous water jacket around it. With abundant coolant in close proximity to the hottest parts of the turbo, internal temperatures are kept in check, never exceeding 350 degrees Celsius, roughly 662 degrees Fahrenheit.

There are multiple benefits to its cool operation. Since the turbo housing never gets insanely hot, further weight savings can be realized because other components mounted in close proximity to the turbocharger do not have to be as aggressively shielded from heat. Additionally the thermal load on a vehicle’s catalytic converter is reduced since the exhaust gets partially cooled as it exits the turbo.

Best of all this is not a science experiment; it works in the real world. This turbo can be found under the hood of MINIs powered by the company’s 1.5-liter, three-cylinder engine. Continental worked closely with BMW. For reference this powerplant delivers 134 hp and 162 lb-ft.

By using aluminum, engineers were able to shave nearly three pounds off the total weight of the turbocharger, but that’s not all. This choice saved money as well. The lightweight metal is cheaper than nickel-based alloys typically used in turbo housings. Their decision to go with aluminum more than offset the additional costs incurred by implementing liquid cooling.
For more on this story, Aluminum Turbos Save Weight, Money and A LOT MORE, please visit AutoGuide.com
 

·
Registered
Joined
·
2,244 Posts
Three pounds is good, but the big weight savings is in the reduced size of the motor (not to mention the engine bay's sheer size) while retaining a desired power level.
 

·
Registered
Joined
·
2,392 Posts
I think adding liquid cooling to the turbo is adding unnecessary complexity. Titanium would be the better material choice if you want to save weight without adding complexity (although it would be more expensive). Maybe restrict titanium for the exhaust side (which would need a much more simple design without cooling) and go aluminium for the compression side?

And the piping etc. of its added cooling is included in the equation of the weigt reduction by the material?
And I thought the catalytic converter needs heat to work well? And how about the added heat load on the cooling system?
 

·
Registered
Joined
·
1,830 Posts
I'm not sure why you would want to cool the gases before they hit the compressor though? Cooling the gases by nature robs some of the energy, which otherwise is transferred to the compressor wheel - this is why companies try to mount the turbo as close to the exhaust ports as possible. The hotter the better, within reason of course when accounting for the heat tolerance of the materials used in the turbo and other associated components.
 
  • Like
Reactions: Ruperts Trooper

·
Registered
Joined
·
7,899 Posts
I'm not sure why you would want to cool the gases before they hit the compressor though? Cooling the gases by nature robs some of the energy, which otherwise is transferred to the compressor wheel - this is why companies try to mount the turbo as close to the exhaust ports as possible. The hotter the better, within reason of course when accounting for the heat tolerance of the materials used in the turbo and other associated components.
Boyle's Law - as EVERY schoolboy knows.
 

·
Premium Member
Joined
·
36,289 Posts
Sorry, it's been a while since I was a schoolboy.

This is about shipboard diesels, but I find it useful:

One of the side-effects of compressing a gas, however, is an increase in its temperature (remember Boyle's Law from high school science class?). Since hot air is less dense than cool air, and therefore contains fewer molecules, hot air burns less efficiently in the combustion process. An optional piece of equipment designed to rectify this problem is the charge air cooler (CAC), sometimes referred to as an inter-cooler or after-cooler.

The compressed heated air, after leaving the turbocharger, passes through the CAC and then on to the engine intake manifold. Also running through the CAC, but separated from the air by tubing, is either seawater or coolant, called salt water after cooling (SWAC) or jacket water after cooling (JWAC), respectively. This intermingling process allows the liquid to absorb some heat from the charged air. The result is cooler, and thus denser, air, which is more advantageous to the combustion process.

Because of the environment in which turbos operate, already mentioned high speeds and high heat (over 1,200 degrees F), the materials and manufacturing processes used for many of these components are necessarily exotic indeed. The turbine housing, for example, is fabricated from spheroidal graphite iron.

This material has good thermal fatigue resistance, and it's strong enough to contain shrapnel-producing turbine wheel "bursts." The bearings used in most turbos are not the familiar ball-bearing type. Because of the speeds at which these components turn, the turbine shaft is separated from bronze journal bearings by a high-pressure oil "wedge," sometimes referred to as hydraulic stabilization, which is thinner than a single human hair. For this reason, when the turbine, compressor, and shaft are properly balanced, they are actually very lightly loaded. However, if a non-running, and therefore oil-wedgeless, turbo blade is turned gently by hand, it may appear to drag.

As long as the blade tips are not contacting the turbine or compressor housings, this is normal. Without the oil wedge, the bearing is not functional. Turbine wheels, living the hellish existence they do, must be extremely durable. These are frequently fabricated form high-nickel super alloys, which will withstand high temperatures, resist corrosion and metallic creeping. Compressor wheels, while not subject to extreme heat, must still be durable and creep resistant (creeping is metallurgist terminology for loss of shape). They are fabricated from copper, silicon, aluminum alloys, which are solution treated and aged. For extremely high-pressure applications, such as high-output gensets, cast titanium is the order of the day.

How does all of this exotic, expensive, and arcane gear enable a turbo diesel to produce up to 50% more power than its naturally aspirated cousins? Diesel engines are air pumps, as are all internal-combustion power plants. They draw fresh air in, compress it, mix it with fuel, burn it, and expel the exhaust. In the process, chemical energy is transformed into heat energy, which then produces mechanical energy.

The turbo-charger simply improves upon this process by forcing more air into each cylinder on every fresh-air intake stroke. More air added to the equation means more fuel can be added as well, and the result is more power from each given combustion event - i.e., each time a cylinder fires. The result is a more powerful power plant without increasing displacement, size, or weight (except for the turbo itself).

The energy, which spins the turbine and thence the compressor wheels, is derived from the high-pressure exhaust gases, which are present whether a turbo is fit or not. The small price to be paid, from a conservation of energy standpoint, is a slight increase in back pressure created by the restriction of the turbo's turbine wheel. This requires the expenditure of slightly more horsepower to expel the exhaust gases during the exhaust stroke. However, in spite of this deficit, the net gain is appreciable. Turbochargers are able to increase a diesel engine's volumetric efficiency upwards of 150%.

Frequent oil changes

As mentioned earlier, not all of this derived efficiency is a free lunch. In addition to the previously mentioned issues of increased impact on the engine and cost, there are other turbo demons with which to contend. Because turbochargers require a constant supply of lubrication for the high-speed turbine-compressor shaft, regular oil changes are even more critical than those for naturally aspirated diesels. The oil supplied to the turbo provides not only the bearing wedge, it also acts as a heat sink, assisting in maintaining workable temperatures within the bearing housing. One of the most common causes of turbo bearing failure is a result of the lube oil's exposure to extremely high heat. When a turbo-charged diesel is run under heavy load for extended periods, it must be allowed to cool off before being shut down. If this turbo cool-off procedure is not observed, a process known as carbonizing occurs. In this process, the lube oil left in the turbo bearing journals literally cooks, leaving behind an abrasive carbon deposit. The next time the engine is started, this gritty substance scores the bearings and clogs oil-supply ports and drains, dramatically shortening the life of the turbocharger and perhaps the engine. When running under heavy loads, these unfortunate circumstances can be forestalled by idling a turbocharged diesel for five minutes before shutting down.


http://www.oceannavigator.com/January-February-2003/Trend-toward-turbos/
 

·
Registered
Joined
·
1,830 Posts
Boyle's Law - as EVERY schoolboy knows.
Well hold on here though, we're talking about the hot side of the turbo in the initial article. I should've corrected myself and said "turbine" not compressor in my response.

Yes, the compressor, or cold side will get hot once you compress the incoming intake charge via Boyle's law.

However on the turbine side you want it as hot as possible as the hot expanding gases will spin the hot side turbine, and thus the attached cold side compressor, faster. Thus minimizing lag. The more heat you shed between the exhaust ports and the turbine, the more efficiency you lose.
 

·
Registered
Joined
·
7,899 Posts
Well hold on here though, we're talking about the hot side of the turbo in the initial article. I should've corrected myself and said "turbine" not compressor in my response.

Yes, the compressor, or cold side will get hot once you compress the incoming intake charge via Boyle's law.

However on the turbine side you want it as hot as possible as the hot expanding gases will spin the hot side turbine, and thus the attached cold side compressor, faster. Thus minimizing lag. The more heat you shed between the exhaust ports and the turbine, the more efficiency you lose.
We don't disagree - hotter is better!
 
1 - 8 of 8 Posts
Top