Recollida de dades i elaboració de les entrevistes

Several factors influence the choice of the combination fuel-power units for the hybrid system. There are especially two factors which are most important - the emissions and the energy efficiency of the system. The choice of the combination type of fuel contra type of

power unit for a hybrid system is also influenced by international agreements between different countries, or agreements within the different countries. This is especially true within areas or countries where the main production of automobiles occurs such as in the US, Japan and Europe.

During recent years the question of fuel economy has grown very strong and in some cases it seems to be more important reducing fuel consumption than reducing the emissions of NOx, particles and other emission components in the exhaust. The many actors being more or less involved in the decision taking or in discussions about the importance of reducing the fuel consumption in vehicles contra reducing emissions and costs may contribute to an uncertainty about which way to go. When estimating the future development of hybrids the above factors have been taken notice of in addition to the technical possibilities for the two main hybrid systems to meet the two main requirements emissions performance and energy economy.

If the development of the hybrid system is to be based only on the requirement of fuel (or energy) economy the fuel/power unit combination should certainly be based on the combination diesel oil/diesel engine today. It is true that the diesel engine is somewhat more expensive to produce and also heavier than the otto engine, but the difference in purchase price for the car manufacturer and the customer will soon be “paid back” by the higher efficiency of the diesel engine unless some unexpected requirement considerably increases the cost of using the combination diesel oil/diesel engine. This is especially valid for heavy-duty vehicles. It is true that there exist some alternative to the diesel engine (see Sections 7 and 8) but the problem is that “the state of the art” of these alternatives is so far not on the same level as the diesel engine and does not have the same market as the diesel engine. Therefore the only real candidate for meeting the fuel economy requirement (or use of energy) seems to be a diesel engine fueled with diesel oil.

If the development of the hybrid system should be based only on the requirement of good emission performance the answer is not quite clear especially in an international perspective.

From a study of the situation in Japan and in the US as a neutral observer, or from listening to the discussion in Europe including Sweden, it is quite clear that there are different opinions about the necessity of using a certain fuel engine combination for environmental reasons. In the USA the car manufacturer Ford presented in 1997 or 1998 a newly developed diesel engine for a hybrid vehicle meeting the Tier II requirements according to presented information – an emission level which, some years ago, not many experts in the field thought it was possible to reach. A study of the presented future emission standards also calls for rather remarkable emission reductions.

Ford, who is one of the “big three” who has signed an agreement with the Government in the USA to do research and development within the PNGV program (see Section 8.1.3) has also signed an agreement with US Department of Energy (DOE) for the development of a hybrid vehicle. From a report (Buschhaus et al., 1998) presented by Ford (see Section 8.2.4) one conclusion could be that DOE was not satisfied with the presented plan to use a diesel engine in the new hybrid vehicle developed by Ford, since, at the time for the presentation of the above mentioned hybrid vehicle, it was agreed that Ford should develop a hybrid vehicle equipped with an otto engine. It is well known that the environmental authorities in the USA and especially in California have some doubt whether the combination diesel fuel/diesel engine of environmental reasons should be allowed to be used in at least light-duty vehicles.

Similar reactions have also been heard in Sweden and up to some years ago only a small number of light-duty vehicles were diesel fueled vehicles.

The opposition against the diesel oil/diesel engine is based on fact that a mass produced diesel engine has far from reached the same low emission levels as a mass produced otto engine. If

looking at the emission standards in Europe for example it can be seen that there is a clear difference between otto and diesel vehicles – vehicles with otto engines being at the lower level. The emissions from diesel engines are still expected to cause a higher health risk than the emissions from otto engines. In Section 8.1.4 a description of emission control systems for both diesel engines and otto engines can be found also for hybrid vehicles. However, the discussion in the previous paragraph about the diesel engine and the opposition within the environmental authorities may have had a decisive impact on the choice of the fuel/engine combination also for hybrid vehicles. The opinion expressed in many countries concerning the diesel engine have certainly resulted in that many companies have used the combination gasoline, ethanol or CNG/otto engine instead of diesel oil/diesel engine in their hybrid system.

In cases when the alternative internal combustion engine is an otto engine there are at least two reasons for using gasoline as fuel. First of all an infrastructure has long existed for the distribution of gasoline and secondly the technology for the combination gasoline/otto engines can easily be copied when producing smaller engines for hybrid vehicles. The fuels which come closest for replacing gasoline are ethanol or methanol. In the question of the gaseous fuels, LPG and CNG, there may be different provisions in different countries but the situation in Sweden is such that natural gas, such as CNG, is certainly preferred to LPG since compressed biogas (which contains mostly methane like CNG) is already used in some cities in Sweden. Both biogas and CNG have are physically two of the “cleanest” fuels for otto engines and they have a good potential of contributing to lowest emissions of harmful pollutants when used in engines dedicated for the use of methane-containing gaseous fuels.

However, experiences from the use of CNG and compressed biogas have shown that the indication that the direct injection otto engine will replace the conventional otto engine within 5 years as the gasoline fuelled alternative for hybrid systems. This is especially true if there will be a positive development of the control system for the hybrid vehicles in line with the presentation in for example Sections 8.1.1 and 8.1.4. Only Mitsubishi has announced that the combination direct injection gasoline engine and hybrid system with an electric motor will be used in order to “deliver super-efficient power generation and performance”.

The development of diesel engine is estimated to have a remarkable impact on the emissions and therefore it will start to make a more positive contribution in the discussion about fuel/engine alternative but this positive movement towards a cleaner engine depends strongly on the cleaning up of the diesel oil. Since it is uncertain whether the diesel engine will have that advantage, attention in a shorter perspective should be called to the fact that there are alternatives available which may take some part of the market from gasoline and diesel oil.

The alternative, in the first place for light-duty hybrid vehicles, is expected to be the ethanol/otto engine and for a heavy-duty hybrid vehicle the CNG/otto engine or the Biogas/otto engine could be a strong candidate.

In Section 5.2 the huge resources of natural gas have been discussed. For a country like Sweden the cost for an infrastructure for natural gas over the whole country would be extremely high and in addition it is uncertain whether there is a common interest among the owners of vehicles in using natural gas as an automotive fuel. However, looking at the situation in Sweden there may exist an interest in using natural gas in certain cities or areas.

One possibility which has been discussed is to convert natural gas to methanol and to produce ethanol from wood as a biofuel.

By the development of intelligent control units and better batteries for the hybrid systems, the internal combustion engine will be operated without rapid transients, which will result in more freedom for the car manufacturer to improve the interaction between the two power systems in the hybrid vehicle. The average energy efficiency of the system will increase, especially during driving in city traffic. In addition to the possibilities discussed in Section 8.2 and Section 12 the model for development presented by TNO may give many positive results.

These improvements of the energy efficiency etceteras may also result in that the car owner more easily will tolerate the higher cost of using alternative fuels.

In a Swedish perspective, building up an infrastructure for natural gas and biogas to be used in vehicles would result in both natural gas and biogas being more attractive as automotive fuels.

The technology for the use of these gaseous fuels in engines would certainly also be affected.

Whether there will be a development in that direction is not certain, as the organizing of a such infrastructure must be based on a political decision. If a decision is taken in Sweden in this direction the use of CNG in hybrid vehicles is estimated to be limited to heavy-duty vehicles.

Since there are also some negative factors connected with hybrid systems, especially in that the vehicle contains more parts and units than a conventional vehicle, the extra weight and the cost of the vehicle is an extra burden for the car owner. The hybrid system may also result in an increasing need for maintenance. There is an urgent need for batteries with higher power and energy densities and the question is when such batteries are to be seen. These disadvantages and especially the cost of the hybrid vehicle certainly have a negative effect on the market, and for a further positive development of the hybrid systems there is a need for large market. The fact that fuel cell technology may have a more positive development and be an attractive alternative sooner than expected may be an obstacle to the development of hybrid technology and especially the drive trains with an internal combustion engine.

In a longer perspective (10 to 20 years) many different ways for the development can be seen and therefore it is not possible to point out a certain direction. The PNGV program and the strong requirement to use “cleaner” vehicles using less energy will have a strong impact on the development of fuel, engines and the body of the vehicle. The development of hybrid vehicle which has been seen has positively influenced the required improvements of the vehicle. There is good possibility, through the use of hybrid technology, to use the internal combustion engine and especially the otto engine more efficiently. Since the hybrid system gives extra weight to the vehicle a lighter body vehicle has been developed and new production technology has been exploited in order to compensate for this extra weight. In addition many units for the control of the different systems of the vehicle have been developed and all of this in a positive way.

In order to sum up the above discussion and the expected development in the time frame of 5 to 10 years it should be underlined that;

- a well pronounced interest in the hybrid technology has been shown among car manufacturers and these who are responsible for the development of hybrid electric vehicles;

- it has been shown that many actors have been involved in the development of hybrid systems for city buses. Unfortunately only a few car manufacturers have been involved in that work. Therefore it is unsure whether the development of hybrid systems for city buses will continue;

- many well functioning hybrid systems for light-duty vehicles have been developed by the car manufacturers especially in Japan and in the USA. This well organized development seems to continue at least in the short time frame;

- the PNGV agreement between the US Government and the three car manufacturers Chrysler, Ford and GM and also other agreements have positively affected the decisions taken among car manufacturers not only in the USA and Japan but also in other countries in order to develop fuel efficient vehicles and among these hybrid vehicles.

In order to sum up the above discussion and the expected development in the time frame of 10 to 20 years it should be underlined that;

- it is not possible make a firm estimation about the development of hybrid vehicles after 2010 to 2015 since there is a considerable uncertainty in some factors affecting a such development;

- two scenarios can be seen concerning the development of energy efficient motor vehicles, namely:

(a) a positive continuation of the development of hybrid electric vehicles parallel to research and development of fuel cells;

(b) a brake through for the development of fuel cells resulting in (1) the use in fuel cells in hybrid electric vehicles with a battery used for storage of electricity and (2) the use of fuel cells as the only source for the delivery of electric power to the traction motor in a vehicle without battery for the storage of electricity use for the traction motor.

- Today it seems most likely that the development of highly fuel efficient vehicle will follow scenario (a) since it is estimated that the fuel cell technology will be to expensive to be used in mass produced vehicles within the time frame of 20 years.

9 EFFICIENCY – FUEL ECONOMY

Iwai, who was presented in Section 8.1.2 (Iwai et al., 1998), has been studying the efficiency of different parts in a hybrid system and also discussing the importance of controlling the interaction between the internal combustion engine and the electric drive train. According to Iwai the efficiency, and by this the fuel economy for a vehicle with internal combustion engine, be improved by;

1) eliminating of engine idling and running the engine at low loads where the thermal efficiency is low and by operating the engine only in points of the engine operational area with high efficiency;

2) accumulating the braking energy at deceleration;

3) installing a power system that can operate with a high degree of efficiency, regardless of the driving cycle;

4) using a bottoming cycle that creates electric energy by driving the power generator with exhaust energy, making it possible to achieve higher efficiency of the system.