The engine has been described as the heart of any car but without fuel, it cannot run. Perhaps, fuel is that blood that runs the car’s heart. Well, a driver will ignite the engine, step on the accelerator and get the car in motion but there is a whole science that happens within that split second.
Shell Fuels brand ambassador, Paul Duke Kaganzi, explains that the vehicle fuel system stores and supplies fuel to the engine.
In the engine intake system, the fuel is mixed with air delivered to the combustion system after being atomized (converted) and vaporized by the fuel injectors.
“The combustion system compresses the fuel in the engine cylinder and ignites it by spark (for petrol) or compression (for diesel) to produce energy. All fuel systems supply fuel to the combustion chamber and control the fuel air ratio,” Kaganzi explains.
Types of fuel systems
Andy Musoke, a motor technician, observes that there are two types of fuel systems; petrol and diesel.
“In the first engines is what we call the carburettor. When fuel is pumped out of the tank, it goes through a fuel filter, and carburettor and every time you step on the accelerator, the jet will squeeze fuel into the inlet manifold and then go into the required cylinder and combustion takes place,” he explains.
He adds that modern engines have a fuel injection system in which fuel is constantly pumped and then into an injector, which is electrically controlled.
It will squeeze a certain amount of fuel into the cylinders at a particular time to allow the combustion to take place.
Different fuels work
How diesel engine fuel works
Musoke says a diesel engine works through combustion ignition of the engine. “Here you have the air it draws straight into the cylinder and is compressed thus heating the air up. When it becomes hot, the diesel is squeezed and because the air is already hot, it causes combustion to take place,” he further explains.
How petro engine fuel works
In short, Musoke adds, the petrol engine has a spark plug while the diesel engine does not. The engine works in a four-stroke system. The upward and downward movements of the pistons during the combustion cycle in a four-stroke engine help to turn a crank shaft which propels the vehicle.
Technically, Musoke explains that fuel used in vehicle engines is produced from crude oil using a refinery distillation process in a fractioning tower.
Simply put, the crude oil is heated up to 400 degrees centigrade.
Disadvantages of the different fuels
“As the crude oil heats up, it distils and separates different fuels and oils at different temperatures as they are collected,” he adds. There are different fuels and oils on the market and Kaganzi says the officially recognized main grade fuels in Uganda are unleaded gasoline (ULG) also called Petrol or Automotive Gas Oil (AGO) or what is commonly known as diesel.
“International environmental protection legislation and standards binding all countries including Uganda have led to the ban or discouragement of importation of leaded petrol or high sulphur diesel. Unleaded petrol (ULG) has been around for more than a decade having replaced leaded petrol whose component chemical lead is considered harmful to the environment. Today we have low sulphur diesel on the Ugandan market,” Shell’s brand ambassador explains.
He adds that vehicles manufactured in the post 1990 and 2000 are built with emission systems which are compliant to the new global emission standards.
These vehicle emission systems are fitted with exhaust particulate breakdown or filtering components (Catalytic converters and Diesel particulate filters) designed to work with the approved fuel ULG unleaded petrol or low sulphur diesel AGO.
Kaganzi also adds that fuelling your vehicle with leaded petrol or high sulphur diesel pollutes the environment and also causes expensive damage to the vehicle emission control system.
Differentiated fuels are base fuels composed with chemical additives which are designed to improve vehicle engine performance, efficiency and protection.
The technical explanation goes to capture the fact that gasoline or petrol fuel differentiation can be achieved by a higher Research Octane Number (RON).
Octanes are a family of hydrocarbons that make up gasoline (petrol). RON is the measure of a fuel’s tendency to burn in a slower and more controlled way.
Higher RON petrol fuel reduces cylinder knock or ping and provides higher compression which delivers a better performance.
How fuel is adulterated
Andy Musoke, a motor technician, says as a mechanical engineer, he only trusts and uses products from recognised fuel stations for fear of adulterated fuel or products, which according to the dictionary, is fuel that has been made impure by adding extraneous, improper, or inferior ingredients.
The technician points to an incident where a driver was served with adulterated fuel. “The fuel was mixed with water and some other stuff which when he ignited the engine, affected the engine. I had to wash the whole engine of these impurities before refuelled at one of the recognised fuel stations,” Musoke recounts.
Shell Fuels brand ambassador, Paul Duke Kaganzi, confirms that fuel adulteration is the illegal introduction of other chemicals or liquid products such as water to a base fuel which results in the product not conforming to the recognised specifications and standards of the fuel product.
He points out that the common purpose of fuel adulteration is to increase quantity of the fuel for increased profit, adding that in Uganda and around the world, a common adulterant used is kerosene (paraffin) because it is from the same hydrocarbon product diesel and petrol is only separated during distillation.
“This makes it hard to detect kerosene in adulterated fuel with the naked eye. In many vehicles, up to 20 per cent kerosene mix will start and run the engine,” he observes.
In 2014, the executive director of the Uganda National Bureau of Standards Engineer Ben Manyindo admitted that although there was a decline in the vice since 2009, fuel adulteration was still a hard problem to stamp out.
Musoke also observes that fuel adulterants once added to the fuel have adverse effects on the motor vehicles, the environment and human health. Kerosene or any other substance once added to the fuel will cause incomplete combustion.
The resultant effect will cause a misfire and damage some components of the valve train overtime.
Incompletely combusted kerosene-petrol or diesel mixture will flood the combustion chamber and end up seeping down the engine cylinder bores.
“The corrosive nature of kerosene will reduce the lubricating qualities of the engine oil in the cylinder bores, in turn causing damage to the fast moving but improperly lubricated pistons,” Kaganzi further explains.
He adds that adulterated fuel cannot be easily detected with the naked eye until it is used to fuel the vehicle and starts to affect the engine performance or pollutes the environment.
However, the use of on spot fuel lab testing kits and special markers on dipsticks can help to detect the fuel adulteration. There are efforts by fuel dealers to combat fuel adulteration. For example, Vivo Energy, the Shell licensee in Africa, has built an inspection, certification and monitoring system in its fuel delivery chain.
“Certificates are issued to all fuel batches at loading points in Kenya and delivery points in Uganda. At all these points, fuel samples are tested for quality or possible adulteration. Fuel delivery trucks are all monitored via satellite tracking. Vivo Energy has set up a modern purpose-built fuel lab at their depot to check samples of all fuel being received or delivered from their depot,” he adds.
Fuel used in the vehicles we drive is composed of hydrocarbons such as methane, propane, heptane, carbon monoxide and other mixtures.
Effects of adulterated fuel on a car
Using adulterated fuel is a big problem in modern engines because of the refined systems in such cars tailored for better atomisation of fuels. Engine malfunctions, failure of components and compromised safety are as results of using adulterated fuel in such cars. Additionally, it leads to increased engine wear, loss of power and crank case dilution — unburned gasoline accumulating in the crank case, then diluting engine oil.
Increased emissions, of hydrocarbons, carbon monoxide, oxides of nitrogen and particulate matter intoxicate the air from such fuels. Experts say health problems could result from harmful tailpipe emissions and cancer causing pollutants, though not all forms of adulteration are harmful.
For instance, small amounts of kerosene added to diesel record insignificant changes in tailpipe emissions.
Kerosene mixed with petrol on the other hand, results in higher emissions because they do not form a uniform mixture, leading to incomplete combustion and even more particulate products.
The high levels of sulphur in kerosene compromises the conversion properties of engine pollutants on the catalysts, leading to engine deposit formation and engine knock. Poor handling of the fuel at adulteration points also leads to pollution and further dereliction of the soil.