My Design Report

Dear All friends of mine
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To be or not to be that is the question for me, I really cannot understand how I came back to the school and joined the MSC programme in mechanical engineering. However, to be honest here, I am interested in learning more about integrated engineering design. The report showed below was one of my assignments this semester. Although it is not a good report in my point of view or in engineering point of view, it is honourable to earn and hear some constructive comments from yours or from those who have ever browsed this page.
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Introduction

Pollutant from Urban Transport
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Urban transport is essential to social and economic development. It enables movement of goods to markets and provides mobility to people for economic and personal activities. But motorized transport also imposes soical and economic costs, one of the most important of which found in Hong Kong is the deterioration of urban air quality. Not to mention the possible sources that may have been come from these chemical factories built in mainland china. In the coming decades, the level of motorization is expected to increase rapidly with rising income in developing countries, and so will the relative importance of urban air pollution from road transportation.
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The costs of air pollutant include reduced visibility and damage to vegetation and buildings, but by farits greatest toll is on human health. Nowadays, most of the vehicles in Hong Kong are air-conditioned. Air pollutants may accumulate to high levels in vehicle compartment if there is no adequate ventilation to dilute the pollutants, or when the air-conditioning systems of the vehicles are not properly maintained. -
Date: 11 March 2008 / Time: 18:25hrs / Venue: Cross-Harbour Tunnel (Hong Kong)
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There are six pollutants categorized as chemical pollutants in Hong Kong like Lead, Particulate Matter (PM), Sulfur Dioxide (SO2), Nitrogen Dioxide (NO2), Ozone and Carbon Monoxide (CO). Sources of particulate pollutants usually include combustion processes, motor vehicles, smoking and industrial facilities. The other part of air pollutant is the gaseous pollutants including all kinds of of gases which will produce adverse effects on our health and environment.
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Why should cabin air filter be so beneficial to vehicle occupants?

Without cabin air filters, pollens, soots, dust and gases, plus unpleasant odors, would pass directly into your car. Drivers and passengers would then be inhaling unfiltered pollutants. It's not only traffic-related and industrial fumes that can significantly impair the health and wellbeing of drivers and their passengers, natural irritant gases like ozone also have adverse effects. A well functioning active air filter can remedy this, because it effectively protects against pollutants and enables the driver to breathe freely.

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It is noticeable that concentration levels of pollutants can be six times higher than on the outside. This is due to the air flow and the fumes which the car in front creates in traffic. This is so-called tunnel effect therefore affects car passengers to a considerably higher degree than pedestrians on the pavement.Vehicle exhaust containing CO, NOx, VOCs, and dust particles etc. from polluted roadside infiltrated into the vehicle compartment may make passengers feel unpleasant, or sometimes sick. The situtation may worsen when the vehicles are stuck in the traffic jam, or passing through the vehicle tunnel, with a polluted environment.

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In vehicles without a cabin air filter, the unfiltered pollutants reach values up to 6 times as high as at the edge of the roadside. Since the air inside a car contains up to six times the concentration of airborne particulates compared with the air outside it, a suitable and effective air filter is very important. Cabin air filter can protect the passengers and driver of a vehicle from airborne particulate which was revealed to be one of the causes of heart and lung disease. Studies show that effective cabin air filters can remove almost 100% (most new air filters are 97-99.9% efficient) of airborne particles and can dramatically improve the quality of air entering the passenger compartment.

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How did the outside air pass into your vehicle cabin?
Let's imagine if we were the driver and passengers or one of them in the cabin compartment of the mini car (say the golden one, see Figure 1 above). the air mixed with vehicle exhaust containing unpleasant gases and particulate pollutants like CO2, NOx, VOCs and dust particles that enters the passenger compartment through the air inlet of vehicle. (See Figure 2)
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The air entering the cabin compartment through the outlet underneath the glove box (see Figure 3 and 4)

The air entering the cabin of the car through the HVAC system and another air outlet underneath the glove box (see Figure 5). Without having air filters, such pollutants plus unpleasant odors would pass directly into our car. All of us would then be inhaling unfiltered pollutants, it is therefore necessary to improve in-vehicle air quality problems and protect against those small particles and fine dust therein.
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Why should an effective automative cabin air quality controlling device be important to vehicle occupants?

Air filters are not 100 percent efficient to trapping dirt particles and controlling the gases pollutants. In general, most of new air filters are 97-99.9% efficient but a small amount of dust or dirt can still pass into the passenger compartment. In addition, it's not uncommon, very often, for cabin air filter replacement to be overlooked by the drivers, especially after several hours of operations or a long distance of travel. If neglected, a cabin air filter can impair airflow in the HAVC system, possible causing interior heating and cooling problems.

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Despite a variety of devices and filters are in use in current market, few of them are extremely effective to those pollutants. The major types of disadvantages are as follow:

1. The existing cabin air filters are easily to be blocked with dirt which will decrease the efficiency of operation. Air filters may not be able to deal with very fine particulate matters, which are rather critical to human health.


2. The existing cabin air filters are not effective to remove gaseous pollutants including carbon monoxide, hydrocarbon, sulphur dioxide and etc.
   
3. Air quality device in combination with a vehicle in using catalysts such as platinum or palladium with rhodium are disclosed to be comparatively expensive to present market.

Those existing filters can only filter particle around PM10 (Particles smaller than 10 micrometers, known as ihalable particles) that may not be able to deal with fine particles (Particles smaller than 2.5 micrometers, also known as fine particles) and it will be blocked after several kilometers of operation. Furthermore they are not effective in dealing with the gasesous pollutants as mentioned above.

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Design Concept for an Automative Cabin Air Quality Controlling Device

It can be seen from the Figures, a synthetic filter media (it is said to be the 1st layer) and a pleated filter material (it is called the 2nd layer) will effectively provide a better filtration with the cabin compartment. It is my team objective to design a high performance and durable device for purifying the airborne substances and filtering toxic and particulate matters whose sizes are smaller than 2.5 micrometers. According to the 1st layer of filter media, it is desired that the media with complex structure will be made of synthetic filter material; all particulate matters (when their sizes are larger than PM10) will be collected or jammed in the filter tissues. After the first layer, it is a second layer of non-woven material that can arrest the remaining dust particles whose sizes are smaller than 10 or between 10 to 2.5 micrometers.

-The stable shape of a sinusoidal curve (see the structure of 2nd layer) which is mechanically stable shape when the condition under normal stage. Two sensible air flow sensors are separately mounted in front of the air inlet and at the outlet respectively. The air flow rate (Q-in) before entering the first layer of synthetic filter and that (Q-out) after leaving the second layer of pleated filter media will be measured and compared with each other. As the major problem found in the existing filters, they are easily to be blocked with dirt or other large scale of particulate matters; not to mention the filtration, such drawback will cause the effiiciency of the filter material not to achieve a longer period of time.

(Figure 7 and 7a: The above sample pictures just demonstrate what the idea I wanted, it is the general filtering materials used in aquarium)
-This device consists of 2 numbers of sensible air-flow sensors, two groups of synthetic filter materials (see figure 7 and 7a), and 1 layer of pleated non-woven material (see Figure 6 above). In normal condition (see Figure 8a), it is said o be the first-four or first-five hours of driving time. The particular matters and other pollutants such as carbon monoxide, sulfur dioxide and the like shall be insulated from these filters, except for those particles whose sizes are classified as respirable particulate matters, say PM25, two groups of synthetic filters become double filtration and purification to the inlet air. The air with pollutants passing through the first layer of filter media will be collected and the fine particles that suspended in the air also be arrested by the pleated filter. The collapse of the pleated filter will then catch the very fine particles because the pleat geometry it is artful way to effectively insulate the particulate matters.

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When the residual pressure drop is increased, it means the particulate matters or dust particles choke the filter media. The sensors will send a signal to the air quality controlling device to extend filter media (see figure 7). I expected that such doing, it seems to be workable but needs to test the empirical idea, could work well as near the project aim as possible. As a matter of fact, the feasibility and design concept are actually bounded up in the hands-on experience. I have taken about 80-85 hours to design, to write and to plan this air quality controlling device. Last but not least, I thank to the HONDA web site that was providing a tool for creating a 360 degree views of the car (say the golden one) with me. Honestly, the pictures can enhance the quality of my design report.

Best Regards

Ken Ngan