Wednesday, August 13, 2008

exhaust flow in an automobile-the future

These days, you can’t think of exhaust system as just some crude plumbing hung on as an afterthought to pipe away air, heat, and to keep those decibels down. It’s become an integral part of the powertrain and under-car architecture critical to performance, fuel efficiency, and emissions reduction. There has already been development of low or zero emission vehicles already in the recent auto shows by major automobile manufacturers like Honda (Natural Gas vehicle) and Ford (Electric car). A oncoming development I would like to discuss about in this section is the Electronic Muffler.

As an executive with Walker, one of the major muffler makers involved in developing the concept puts it, "After the introduction of the catalytic converter in 1975, this is probably the most revolutionary technology that’s happened to exhaust systems in the entire history of the automobile."

While the idea is surprising, the basic principle isn’t hard to grasp. From a microphone and a crankshaft speed/position sensor, the computer receives input on the pattern of pressure waves (that’s what sound is, after all) the engine is emitting at its tail pipe. This data is processed using patented algorithms, which produce mirror-image pulses that are sent to speakers mounted near the exhaust outlet, creating contra-waves that cancel out the noise. In other words, the sensors trap the waveform signature of the engine, and the speakers generate anti-noise waves 180 degrees out of phase with the gas waves. This destructive interference idea is sort of like fighting fire with fire. The sound waves collide, wiping each other out. It doesn’t just mask the noise, it actually removes sound energy from the environment, and from the law of conservation of energy where the energy has to turn up someplace, all that is left is low-level heat.

Although electronic mufflers are not widely used (if ever) at present, they may be installed on vehicles in the near future. In 1989, a joint Electronic Muffler System development program was started and the University of Michigan’s Delphi study predicts that 20% of the cars produced in North America will have electronic mufflers by the turn of the century.

Well, if the electronic mufflers are really as effective as they claim to be and they were available now, we could build a perfect exhaust system using the setup described earlier with the addition of an electronic muffler then the problem of loud exhaust wouldn’t exist. But then again, by the time the electronic muffler is out in the market, technology might have other improvements of the exhaust system and we will again try to match components to produce more horsepower and attain better gas mileage (efficiency).

In conclusion, we go back to the basic analogy of the engine as a pump; the more air that can flow freely, the more horsepower that can be optimally achieved from the engine. This research paper has only dealt with how to get air OUT of the engine. It is important to note that the INFLOW of air also influences the output performance of the engine. As a matter of fact, we need the inflow of air before the outflow process starts. In brief, the inflow of air can be modified by removing the intake resonator, or even removing the entire airbox and installing a pipe with a cone-shaped filter at the end. There are many other ways to improve air inflow, but I shall not discuss about them as it would be outside he scope of this paper if I’m primarily interested in the outflow of exhaust gases.

Also, it is important to note that "horsepower" is a unit of energy over time. So the more energy it requires to do something, the less power you will get out of it. In other words, it is because motorcycles are lighter than cars that they can achieve similar if not higher horsepower. That is why race cars are stripped of the interior, air conditioning, and any other unnecessary weight. This way, there will be less weight to move, meaning less energy required and thus more power produced. That is why automotive engineers are trying to use materials of lighter weight, like plastics and carbon fiber.

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