Doktorarbeit / Dissertation, 2018
89 Seiten, Note: 3.91
Abstract
Introduction
1. Historical context of motor vehicle technology and development of
Innovations
1.1 Engines
1.1.1 Otto engines
1.1.1.2 Octane in Gasoline or Petrol fuel
1.1.1.3 Ignition timing
1.1.1.4 Engine head and valve train
1.1.1.5 Test methodology
1.1.1.6 Conclusion of this chapter
1.1.1.7 Engine wasted power by valve train load
1.1.1.8 Test methodology
1.1.1.9 Conclusion of this chapter
1.1.1.10 Electrical consumers cause increased emission of harmful gases
1.1.1.11 Test methodology
1.1.1.12 Conclusion of chapter 1.1.1.10
1.1.1.13 Air conditioning causes increased pollution
1.1.1.14 Test methodology
1.1.1.15 Conclusion of chapter 1.1.1.13
1.2 Transmissions
1.2.1 Manual gearbox and clutch
1.2.2 Automatic gearbox
1.2.3 Test methodology
1.2.4 Conclusion of chapter 1.2.2
1.2.5 Vehicle wheels geometry
1.2.6 Test methodology
1.2.7 Conclusion of chapter 1.2.5
1.3 Vehicles drag koeficient
1.3.1 Test methodology
1.3.2 Conclusion of chapter
1.4 Tires
1.4.1 Test methodology
1.4.2 Conclusion of chapter 1.4
Literature
This dissertation analyses and explains influence of engine and vehicles constructions to fuel consumption and emission of harmful gases. In following text, it is clearly stated how new innovations, on mostly, personal vehicles contributes to increased air pollution and some clever innovations which contribute to reduction of air pollutions are ignored just in interest of car's manufacturers and the profit they make keeping technology as it is. It is quite explicit, that most of innovations made on recent manufactured cars are done just to attract buyers, as such modifications improve the vehicle's performances but do not contribute to green environment as it is put out every time when new model comes out from factory. On bellow written chapters several examples are stated where is clearly explained how some existing technologies can be used to reduce emission of harmful gases as well as some suggestions of modified technologies which would also contribute to reduction of air pollutions.
When we calculate the possibility of reduced fuel consumption and thus reduction of air pollution which is roughly stated in below written chapters, we will come to the conclusion that emission of harmful gases can be reduced up to 50% on personal motorcars which make the majority of vehicles worldwide.
When first introduced in commercial market, the goal of internal combustion engines was to replace the horse's physical strength used to pull carriages. As the early engines were very unreliable and inefficient as well as transmissions, vehicle steering and suspensions, innovations in large specter of new ideas and solutions are implemented in the industry of motor vehicle technology, but without paying much attention to air pollution. The first serious attempt to reduce air pollution was proclamation of Clean Air Act in 1970 by EPA (Environmental Protection Agency). EPA and the state of California took the lead in the control of vehicle pollution. Since than, great results are achieved in this field, but among thousands of innovation implemented in the automotive industry during last several decades great number of them are rejected just for the reason as they were unprofitable. In other words, very bright innovations were never implemented in vehicle's industries regardless of possible improvements in vehicle performance, safety and particularly air pollution, just for the reason as such technological improvements increase the cost of productions and thus reduced the profit. The new demands of the market, competitions and new laws related to the emission of harmful gases forced the manufacturers to improve motor vehicle technology day after day. This dissertation, trough researches, describes and discusses development of motor vehicle technology, achieved improvements during the time as well as possibilities of greater improvements in case of implementations of new ideas which are, in most cases, unacceptable for manufacturers because of higher production cost, or sometimes reduced performances, but would have a great influence in reducing emissions of harmful gasses.
Just for introduction, first automobiles were powered by external combustion engines or steam engines which operation principle will not be discussed in this dissertation. Rapid development of internal combustion engines technology in the 1900s replaced steam engines in automobiles almost over the night.
Basic principle of internal combustion engines operation did not change since invented. From the very beginning of automotive industry many imperfections of internal combustion engines are noticed which challenged engineers to bring up numerous innovations to improve efficiency, power, fuel consumption, emission of harmful gasses etc. Internal combustion engines are divided in two groups, Otto and Diesel engines, or Petrol and Diesel engines, and further divided in subgroups as two and four stroke engines. Four stroke Otto and Diesel engines are generally used in automotive industry. The third type of internal combustion engine is rotary or Wankel engine. This type of engine is rarely used in automotive industry and will be not discussed in this dissertation.
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Two stroke engines (Image 1)
Above sketches show simplified working principle of two stroke engines. This engine has many advantages compare to four stroke engines, but also many disadvantages. Advantages are: simplicity, lightness and twice the power produced in each engine revolution compared with four stroke engines. Beside that, such constructed engine does not use inlet and exhaust valves and therefore no resistance exists by resistance of valve springs or friction caused by valve train.
On the other hand, this type of engine has more disadvantages than advantages. Therefore they are rarely used in automobiles. First disadvantage to mention is durability. This type of engine has not oil lubrications under the pressure distributed all around the moving parts in the engine. Engine moving parts are lubricated by around 2- 4 percent of oil mixed with petrol which powers the engine. Such lubrication drastically reduces engine durability.
Working principle of two stroke engines is quite simple and produces power in every engine cycle, contrary to the four stroke engines which produce power on every other crankshaft cycle. In first engine stroke when piston moves from TDC or top dead center towards the BDC or bottom dead center, inlet port closes and air fuel mixture is pressed into the engine cylinder. In the same time, gases from previously power stroke are leaving combustion chamber additionally pressed out by pressurized air fuel mixture formed in the crankcase. On, let's say, second stroke, when piston is traveling towards TDC, exhaust port closes and air-fuel-oil mixture is compressed and power stroke occurs.
In such combustion we can see many disadvantages of two stroke engine. Firstly, fuel is mixed with 2-4% of oil to enable lubrication of crankshaft bearings and piston. Secondly, emission of burned, or partly burned, gases is highly polluted. The third disadvantage is air-fuel-oil mixture which unburned leaves the combustion chamber during the inlet-exhaust cycle. This part of two stroke engine can be compared with four stroke engine valve overlap discussed in further text.
Almost the same principle of two stroke engines applies to Diesel engines. The only difference is that instead of air fuel mixture the only air is sucked into the crankcase and fuel is injected additionally at TDC.
Working principle of four stroke engines is explained in chapter 1.1.1.4 Engine head and valve train.
Otto, or better known as Petrol, engines are invented, or one may say designed, by Nikolaus August Otto in the second half of 19th century. Why the word design is more commonly used in such situations rather than invention? Invention is by its definition something entirely new while innovation is a composition of, more or less, known technologies and materials which finally make something new. Therefore, in this dissertation, expressions as design and innovations will be used for new ideas and improvements achieved in automotive industry. Most of ideas and innovations commonly occur accidentally when ordinary people or engineers encounter problem in some already developed projects. This is the case with Nikolaus Otto. He was a salesman who traveled almost all over the world. It happened that he has seen one of the first internal engines build in Paris by Belgian emigrant Jean Joseph Etienne Lenoir. Aware of poor efficiency of such designed engine, Otto tested the replica of Lenoir's engine and come up with idea of using compressed air-fuel mixture and drastically improves the engine efficiency. So, this is how it started with, let's say, efficient internal combustion engines powered by Gasoline fuel and air mixture. The following drawing (Public domain) shows the first Otto one cylinder stationary engine.
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Otto engine (Image 2)
In early days of internal combustion engines, the numbers of different fuels were used to power the engines. In all cases the large amount of fuel was wasted. Otto engines have had difficulties to fully ignite most of used fuels, thus efficiency was very low. A later development of Diesel engines improved burn the heavy fuels and oils.
Here, we shell leave the long history and list of people who contributed in early days of automotive industry as Gottlieb Daimler, Wilhelm Maybach and many others and focus to the innovations which made today's automobiles modern and efficient as they are.
In the beginning of development of gasoline engines, it was very obvious that more power is obtained if air-fuel mixture is progressively burned rather than obtaining the power from sudden air-fuel mixture explosion. From then on, innovations made a rapid rise in engine modifications.
First serious innovations on four stroke Otto engines were related to electrically ignited air-fuel mixture and fuels which will resist self-ignition when mixed with air and compressed. Early engines were powered by, so called, straight run gasoline which was a byproduct of crude oil distillation. Despite of very low engine compression ratio, result of using such fuel was abnormal engine knocking and pre-ignition. That means that compressed air-fuel mixture detonated in the engine cylinder before piston reached the top dead center. Thus, instead of forcing the engine piston down after it passed the top dead center, detonation partly pushed piston in its opposite way. It is not difficult to conclude how much power was wasted and how enormous fuel consumption was. Even worse, emission of harmful gases from unburned air-fuel mixture was extremely high. To overcome such big problem some fuel additives had to be found to resist auto- ignition caused by pressure and temperature during the compression cycle of four stroke engine. In early 20th century every automotive manufacturer was searching for chemical
which will resist self-ignition of the air-fuel mixture. Finally, it was discovered that lead mixed with fuel would reduce engine knocking caused by pre-ignition. Here, we shall see very clear example where the bright innovation where not accepted in automotive industry just for the reason of losing the great profit, even if such decision is deadly dangerous for billions of people. Namely, in the same time some more chemicals, benzene and ethanol, are discovered which can provide octane in fuel. Despite the critics and the resistance of the whole world against the leaded fuel, it dominated worldwide until late 1970s when unleaded fuels started to be sold and used by law.
References:
The History of Leaded Gasoline
https://articles.mercola.com/sites/articles/archive/2015/10/10/leaded-gasoline.aspx
The U.S. Experience ith the Phasedo n of Lead in Gasoline Richard G. Ne ell and Kristian Rogers*
http:// e .mit.ed /c olstad/ /Ne ell.pdf
When octane value was implemented in Gasoline or Petrol fuel, many things changed in sense of modifications in internal combustion engines. Day after day, so many ideas and innovations were brought up that gasoline engines with very low revolutions per minute and low output power, rapidly turned to very efficient and powerful engines.
Fuels with added octane resisted auto-ignition of fuel and thus reduced engine knocking or pinging, which is also common expression for engine noise caused by early ignition, or auto-ignition of air-fuel mixture. With new octane fuels, realization of many innovating ideas became possible. The one of the first ideas were to increase the engine compression ratio. It was quite obvious that air-fuel mixture compressed in higher stage, when ignited, could produce more power than the same amount of air-fuel mixture compressed at lower stage. Certainly, until then, implementation of such idea in action was impossible because of problem with self-ignition of air-fuel mixture in even very low engine compression ratio. Octane fuel ratings are expressed in numbers. Most usual octane grade fuels were Regular fuel octane graded by number 87 or 89 (earlier fuels even with number 85) and Premium fuel octane graded with number 92 or 93. Of course, today's fuels with much higher octane value are offered on market. The use of the specific octane grade fuels are determined by vehicle manufacturer and mostly depend of engine compression ratio of particular automobile model. The following table and chart of engine compression ratio and octane value in the fuel shows approximately how the compression ratio is related to octane value in the fuel.
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Octane value in the fuel (Image 3)
That is to say, that octane implemented in petrol fuels enabled engineers to start increasing engine compression ratio to obtain more power from engine using the same amount of air-fuel mixture. Further more, with such modification when air-fuel mixture is maximally compressed, and thus more efficient burn of fuel is obtained, emission of harmful gases were considerably reduced. As octane values in fuels were increased during the time, the possibility of increasing engine compression ratio was further allowed resulting with increased engine power, more efficient burn of air-fuel mixture and reduced emission of harmful gases. From all this we can conclude that octane made great improvement in air-fuel mixture in internal combustion engines. As almost all advantages of octane fuels are exploited at that time in sense of obtaining maximum power from engines, engineers focused on ignition timing of air-fuel mixture in the compression cycle of four stroke engines. Namely, when compressed air-fuel mixture is ignited by electrical spark, flame in compressed air-fuel area needs some time to spread over and fully ignite its volume just in time when piston passes the top dead center in order to push the piston down in its power stroke with all its strength.
As said previously, air-fuel mixture needs some time to ignite. Here will be explained basic system of air-fuel ignition and modification which have been made during the time to improve proper and full ignition of mixture. All this is important to understand researches, questions and hypotheses in this work.
The spark timing on very early engines was fixed. Spark timing was set at calculated time before TDC (top dead centre) of engine piston. Such ignition timing was fairly good when engine was running at constant speed RPM (revolutions per minute). When RPM was increased, timing was too late. As mentioned, air-fuel mixture needs some time to ignite completely just at the moment when piston passes TDC and pushes the piston down with all its power. This was achieved by setting the timing for particular RPM. When RPM was increased and piston moved much faster toward the TDC, time of air-fuel ignition was shortened. That means, mixture did not have enough time to ignite completely and ignition was prolonged during the time when piston passes TDC. In such case, air-fuel mixture reaches full ignition quite late and considerable loss of power occurred. To overcome this problem, engineers made several modifications to enable spark to occur in the specific time related to RPM. In fact, mechanical or electronic device was needed to distribute sparks on each engine cylinder at specific time, late ignition at low RPM and advanced ignition at high RPM.
First modification was made by installing movable breaker points plate in the distributor. As most readers would know, the breaker points are placed on breaker points plate where the points are opened and closed by distributor spindle cams. Cams will lift one part of the points at the desired time in which spark occurs. By installing movable breaker plate connected with linkages to the dashboard, or more often to the center of steering wheel, driver was enabled to adjust ignition timing during the driving. We can assume that motorcars drivers at that time had to be well educated to drive. They had to have a basic knowledge of engine technology to properly advance or retard ignition timing. Thus, when engine was idling, breaker points plate had to be retarded to its basic position as calculated by engineers when basically tuned the engine. As vehicle accelerated the engine RPM increased and ignition timing had to be advanced. That was done by moving the linkage lever forward and opposite when vehicle decelerated. By moving the breaker plate left or right distributor cam will open the points earlier or later and spark will occur at the right time, certainly, if driver was well educated to make right adjustment at the right time. This improvement was certainly great and improved engine efficiency as well as fuel consumption and automatically reduced pollution. But, such vehicles were definitely unsuitable for ordinary people who did not want to be drivers and mechanics to own a motorcar.
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Centrifugal advance (Image 4)
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Vacuum advance (Image 5)
As advanced timing problem was solved, engineers focused on automation of timing advance to enable automotive uneducated people to own and drive personal vehicles. To achieve automatic advance timing, the centrifugal weights and springs are added underneath the brake points plate. Instead of adjusting ignition timing manually, the centrifugal weights and springs took over that task. As distributor shaft is turning faster or slower the centrifugal weights are expanding or contracting and accordingly adjusting breaker plate position. As expanding of centrifugal timing advance takes some time, system was further improved by adding small vacuum pump to distributor linked to breaker plate. Vacuum pump linked by tube to carburetor reacted on depression in carburetor and proportionally promptly advanced breaker plate. This vacuum pump overcomes the problem with delay of centrifugal advance. In general, knowing that air- fuel mixture is proportionally sucked into the engine trough the carburetor and timely ignited by spark, we can conclude that such engines were ready for mass production with more or less acceptable pollution. Why more or les? During the time so many innovations are implemented to reduce pollution that such concept of engine would have minimum pollution if engine performance did not take priority as well as ignorance of innovation which are to expensive to be used in automotive mass production.
In order to improve engine RPM and achieve the spark occurrence at the precise time, engineers attention was focused to elimination of mechanical breaker points which limited RPM at high engine speed as well as they limited accuracy of air fuel ignition. On seventies, when electronics replaced most of electromechanically operated systems in industries, automotive engineers were able to improve the function of timing distributor and modify the breaker points with, so called, transistor assisted ignition. This was the first step in modifying accuracy of air fuel mixture ignition by use of electronics.
In electromechanical breaker points system, a breaker points, or simpler said switch, break the electrical circuit at determined time for each cylinder when high voltage is induced in the ignition coil. Certainly, accuracy of ignition timing as well as value of high voltage depends of, so called, dwell angle and cleanliness of breaker points contacts. Determined dwell angle, the time when breaker points are closed, allows enough time for high voltage to be formed in the ignition coil. Cleanliness of breaker contacts will allow sufficient current to flow between the battery and ignition coil. Lack of time caused by irregular dwell angle or partly burned breakers contacts will result with drop of high voltage on spark plugs and thus poor ignition of air fuel mixture. To partly overcome the duration of closed points and avoid burned surfaces of breakers contacts, a transistor is used to solve this problem.
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Electromechanical ignition system (Image 6)
On the first drawing shown above, the electromechanical ignition system is sketched. In simple words, current flows from battery to the ignition coil. To make circuit closed, breaker contacts are connected and coil is charged. When contacts open on the cam lobe, electrical circuit is open and coil is discharged trough the distributor cup to determined spark plug. Shown condenser is used to absorb sparking between contact points when they start to open. But, even condenser can not absorb sparking between contacts absolutely. Some small sparking will still occur between the contacts and by the time will make the contacts surfaces partly burned and reduce the current flow trough the ignition coil.
The second drawing shows the same electromechanical ignition system where transistor is implemented and capacitor removed. So, where is the advantage? Unlike the situation in previous case where current flows over the breaker points, in this case current flows directly trough the transistor to the minus pole of the battery without any obstructions and drop voltage. Voltage of very small value flows from the transistor over the resistor to the breaker points which does his job as previously described. Transistor, as a switch, is very fast and dwell angel accuracy can oscillate a bit. As current is very low between the breaker points, there is not any burn deposits on the contacts ad current can flow freely.
Finally, before computerized ignition system was implemented, fully transistorized ignition system was developed and all imperfections of two previously described ignition system are solved.
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Transistorized ignition system (Image 7)
Here, we have almost identical ignition system as previously described, but fully transistorized. This is contactless system which consists of transistorized module, rotor with lobes, pick-up coil and magnet. Simple said, whenever one of the rotor lobes approaches the pick-up, signal is sent to the module which opens and closes electrical circuit in the ignition coil. As we can assume, this electronically operated ignition system is very accurate and spark occurs at determined time on the spark plug.
In this chapter we shall discuss about innovations which have been made on engines to increase its performances but not paying much attention to pollution. As previously explained, engines design reached satisfactory level. Such designed engines with today known modifications which can further reduce emission of harmful gases would produce enough power to drive the personal vehicles sufficiently well. Knowing that, all over the world, vehicle's speed is restricted to 80 Miles even on highways, it is absolutely senseless to manufacture powerful high performance cars. As driving such vehicles with drastically limited speed does not make sense, these cars should be highly taxed. Namely, most of today's cars could be perfectly run by engines with a half of power then they have. Reducing power and using today's technology means cutting fuel consumption by almost fifty percent and thus pollution also. How owning the personal vehicle is in most cases a prestige, demand for performance cars on world's market is great, regardless of limited use of their performances. Therefore, where demand exists there is a profit. Where the profit is high, law is tolerant. Until eighties law was quite tolerant regarding high fuel consumption and emission of harmful gases. Thus, car manufacturer used all efforts to design powerful engines and compete with competition.
To compete on market, manufacturers worked very hard to attract potential buyers with new designed exteriors and rich looking interior. Along with these novelties, engine power increscent was inevitable. Regardless of engine capacities, engine power could be increased by improving air-fuel intake and exit of burned gases. With such improvements, engine of the same capacity would produce much more power. Widening the inlet ports and valve heads to its maximum, much larger volume of air- fuel mixture entered engine cylinder and thus produced much more power on combustion stroke. As the inlet valves were widened to its maximum, the same thing was done with exhaust valves. To speed up exit of exhaust gases even more, exhaust manifold was separated in tubes for each cylinder and joined in one or two tubes quite far from engine. Concerning maximum power which can be obtained from an engine, excluding electronically controlled engines and supercharged and turbocharged engines, these innovations would be a final step for design of powerful enough engine whose harmful gases could be successfully controlled.
Now we are encountering first problem when increasing the engine power which will have the negative effect to the environment. It is not surprising, as people always want to achieve more and more even when some ideas could be harmful. The goal of new improvement was to bring more air-fuel mixture into the engine cylinder. The idea was quite simple and used even today, but causes increased fuel consumption and thus pollution too. This innovation is called engine valve overlap. Before we come to the point, let's see standard valve opening during the engine's four cycles:
Intake - Compression - Power - Exhaust.
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