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Fuel economy and fuel efficiency

Md.Alamgir
Every individual and institution has to assess and analyse the energy systems to identify the areas of savings and to act accordingly to save fuel, with corresponding savings on cost and CO2 emissions.***
Fuel economy and fuel efficiency” is a widely discussed topic in the world. Fuel economy is dependent on fuel efficiency and people's activities related to fuel consumption. Although these two terms are well known to the people in general, the technical term "fuel efficiency" may not be easily understood by every one. It is now important for every citizen to understand the term and to take individual responsibility to increase fuel efficiency for reducing fuel consumption that will in turn save our economy and prevent environmental pollution. It is true that if one is sincere about maintaining fuel efficiency of the machinery and equipment he uses in his day to day life, saving fuel cost is possible. In the context of fuel price hike, I would rather say hiking price will compel the people to know about increasing fuel efficiency that may help adjust their fuel cost within their ability, and at the same time contribute to national economy and environment.
Let us first try to have an understanding of fuel energy and efficiency. Fuel oil is a complex mixture of a wide range of hydrocarbon components having an internal chemical energy of 42 to 50 Mega joules per kg. Joule is the unit of work. Force is the result of multiplication of mass and gravitational acceleration. Gravitational acceleration is 9.81 meter /second2.1 kg mass is equivalent to 1 x9.81 Newton (N) or approximately 10 N force. Therefore, if someone is lifting 1 kg force, it can be said that he is lifting 10 N force. If 10 N force or 1 kg mass is lifted by 1 meter, it is said that a work of lON-m or 10 Joule has been done. Having a clear conception of unit of work, power and energy can now be understood. Power is the work done in every second by any machine or equipment. Energy is the ability of doing work and is expressed as the quantity of work. One kg fuel of 42 Mega Joules calorific value, if burnt, would have an ability to lift 42 Mega Newton or 4.2 Mega Kg (1kg = 10 N) by 1 meter. 4.2 Mega kg means 4.2 million kg or 4200 ton mass. However, until today no engine manufacturer has been able to utilise the full energy released from burning fuel. Even half of the released energy can not be utilised. The best makers' engines are able to utilise about 45 to 50%. The rest of the energy is wasted mostly in heating the environment. The more fuel we burn the more we heat up the environment, adding to the fear of melting polar ice and consequently rising seawater level. At the same time carbon dioxide and other pollutants are emitted proportionately with the amount of fuel burnt.
Manufacturers have tried their best all the way since invention of diesel engine to maximise the utilisation and reduce the waste. Present days' specific fuel consumption is claimed to be as low as 160 gm/Kw-h by some manufacturers. That means if an engine of 1 Kw (1000 joule/ sec) rating runs for an hour (3,600sec), it will consume 160 gm fuel oil. 1 Kw- hour or 3.6 Mj energy is obtained in expense of 160 gm fuel. 160 gm fuel contains 6.72 Mj energy (0.16 X 42 Mj = 6.72 Mj). Therefore overall efficiency= (3.6/6.72) X100 = 53.6%. Efficiency of a machine or equipment is again reduced due to the lack of maintenance and in many cases due to the ignorance of end users.
So, half of the released energy from fuel just heats the environment and a small portion is dispersed as friction and sound. It is worth mentioning that 1 kg fuel mixes with about 25 kg air during the burning process and subsequently 26 kg burning products are being dispersed into the atmosphere. The atmosphere on top of our spherical planet of about 12750 Km diameter consists of layers of air of about 100 Km thickness. Three quarter of the atmospheric mass is within 11 km from the surface. It means we are continuously pouring pollutants into a limited atmospheric volume. Is that not disastrous?
It will be wise to demonstrate the realisation of fuel economy and fuel efficiency by some examples. Someone uses a washing machine to clean and dry his clothes. But if he thinks about fuel economy he will wash the clothes by hand and dry them in the sun. His use of manual and solar power to alleviate the fuel crisis may seem too small. But it is sure that if every citizen thinks like him and does the same thing, it may make a great contribution to the nation's fuel economy.
In my building there is an electrical lift. I stay on 3rd floor and always try to avoid the lift, saving the much-needed electricity. In return, I get health care free of cost -- physical exercise that helps me to remain fit. At the same time I contribute to fuel economy.
Good housekeeping helps fuel economy. Vacuum cleaning of the condenser coils at the back of air conditioning units and fridges contributes to fuel economy. Accumulated dust reduces their efficiency by up to 25%, adding that cost to the electricity bill. Defrosting frozen food inside a fridge makes the fridge compressor run less. Maintaining the car engine -- cleaning air filter, keeping tires at the correct pressure — and avoiding traffic rush hours will help run a car with higher efficiency, thereby contributing to fuel economy.
Fuel economy depends on how effectively a consumer manages his energy. It is possible to substantially reduce fuel consumption straight away and without major investment. Areas that need to be paid attention to immediately are machines running with a non-optimal load, non-optimised energy consumption in the working environment (lighting, ventilation, operation during breaks, night operation), and reduced level of engine efficiency due to aging machines. Every individual and institution has to assess and analyse the energy systems to identify the areas of savings and to act accordingly to save fuel, with corresponding savings on cost and CO2 emissions.
The writer is an Engineer Surveyor in an International Ship's Classification Society.