What Is Diesel? Expert Insights
Written by: Marion Hanson, Last updated:18th October 2024
Diesel engines are an essential part of the fleet industry, allowing your fleet vehicles to travel to and from different destinations safely and smoothly.
Reliance upon fossil fuels first arose out of necessity. When first invented it was the best method of fuel that was available at the time.
When was diesel invented?
In the 19th century, in particular, the oil was made out of whale oil which had terrifying effects on ocean life. Luckily, in 1854 a cleaner-burning, more abundant and easier-to-produce alternative was invented, this fuel was also easier to produce and was made by Canadian geologist Abraham Pineo Gesner through the distillation of crude oil, making it better for the environment than the original fuel.
From there on, further petroleum products were manufactured such as petrol and lubricants to serve industry (including fleet vehicle) needs.
What are diesel engines?
Diesel engines are a type of internal combustion engine which presents across multiple applications, including fleet vehicles. It can also be used to generate heat and electricity.
Diesel fuel is named after the diesel engine for which it is manufactured, not the other way around. It got its name from the inventor, Rudolf Diesel.
What is the difference between diesel and petrol?
Diesel engines differ from petrol engines in that they operate in a compression ignition engine. This means that they use high pressure to combust it’s fuel, instead of an ignition source (with petrol engines being fired up by a spark)
Another key difference is the fact that diesel is heavier than gasoline, this means that it evaporates slower whilst emitting fewer amounts of CO2 and methane, but unfortunately producing higher levels of nitrogen compounds in the process.
How much is diesel per litre?
The average diesel price in the UK in August 2024 is 152.79p per litre as of the latest update by the RAC. Whereas, this can fluctuate on a day-to-day basis based on industrial events.
How many miles per litre of diesel?
The number of miles you can get per litre of diesel depends on various factors, including the type of vehicle, driving conditions, and driving habits. However, on average:
Small to medium diesel cars
Typically achieve between 15 to 20 miles per litre (mpg equivalent of 68-90 mpg).
Larger diesel vehicles (e.g., SUVs):
Usually get around 10 to 15 miles per litre (mpg equivalent of 45-68 mpg).
These figures can vary based on factors such as highway vs. city driving, vehicle maintenance, and load. For more accurate data, you should check the specific fuel efficiency ratings for your vehicle model.
Benefits vs considerations of diesel
Benefits of diesel
Diesel has got great mileage, with 25 to 30 percent better fuel economy than similar-performing gasoline engines. This is due to it being the most efficient and energy-dense fuel available as it contains more usable energy than gasoline.
Another benefit is that diesel contains no spark plugs or distributors, meaning that it will never need ignition tune-ups.
When it comes to diesel engines, they are built to withstand the rigors of higher compression. They usually last much longer than gas-powered vehicles as a result of this, meaning they will require fewer major repairs in this department.
Storing this fuel is efficient due to it being able to be kept stable at natural temperatures and operable for most temperatures experienced throughout the year.
Considerations of diesel
As with all benefits also come some considerations to think about, particularly regarding sustainability factors. This is because diesel produces high levels of emissions. This has particularly become prominent in recent years and has led to the rise in popularity of electric vehicles (EVs), but it is important to remember that even EV vehicles have compromises of their own.
Non-renewable, air-polluting options can be blended with renewable drop-ins to eliminate this issue, this also helps with the downside of oil drilling to extract fossil fuels that make this diesel and any toxicity to the environment.
NOx content and sulphur can also be present in some diesel meaning that only buying high-quality diesel which meets Euro VI standards and is ULSD certified is crucial.
FAME content means diesel is hygroscopic (meaning it attracts water) and results in clogged filters and engine breakages (FAME-free alternatives do not have this issue)
Diesel petrol fleet uses
Whilst diesel is usually associated with passenger cars, it can also be used to power machinery in the construction industry.
Some of these vehicles include vans, lorries, buses, coaches, tractors, harvesters, cranes, bulldozers, diggers, forklifts and rail transport.
Fuels that can be used in diesel engines
Different types of diesel fuels have been authorised to be used within different diesel engines, these include:
What is red diesel (gas oil)
Red diesel fuel is used in off-road vehicles and machinery. Although it is the same as regular diesel, it is marked with a red marker (dye) to prevent illegal use on road-going vehicles.
Paraffinic diesel (such as HVO fuel or GTL fuel)
Paraffinic diesel usually has a very high cetane number with no sulfur, nitrogen, oxygen or aromatics included. Paraffins can be produced with various processes from either fossil fuels or neweable feedstocks. Alternatively, synthetic fuels are produced by gasification and Fischer-Tropsch (FT) which is the liquefaction of natural gas (GTL) and coal (CTL).
Biodiesel
Biodiesel is a renewable, biodegradable fuel manufactured domestically from either vegetable oils, animal fats or recycled restaurant grease. Biodiesel meets both the biomass-based diesel and overall advanced biofuel requirements of the Renewable Fuel Standard.
These different types of diesel are all produced to meet different specifications that are intended for that specific type of fuel. Before switching to any alternative fuel you should always check your engine’s warranty to ensure it covers alternative fuels.
How does diesel fuel work?
Diesel engines have a wide range of applications, but the basic operation is largely consistent, as most are four-stroke engines. This means power is generated through a series of four stages (stroke cycles), which we will explain below.
Before the engine begins operating, fuel is pumped from the tank to the engine. The fuel passes through a filter that removes any contaminants—like bugs, dirt, or, in cold conditions, waxed FAME biodiesel, which can cause significant issues during winter. To assist farmers, refineries sometimes reduce the 7% biodiesel content in red diesel used in agriculture during colder months.
Stroke 1: Intake stroke
The fuel injection system delivers the correct amount of fuel, which is mixed with air in the pistons. This mixture is then compressed.
Stroke 2: Compression stroke
The intake valve closes, and the mixture of air and fuel is compressed within the cylinder.
Stroke 3: Combustion stroke
Under high pressure, the air-fuel mixture ignites, leading to combustion and the release of energy.
Stroke 4: Exhaust stroke
The exhaust gases from combustion are expelled through the exhaust valves, pass through the exhaust manifold, and enter the turbine side of the turbocharger.
Turbocharger
After the exhaust strokes, the remaining fuel fumes are sent through to the turbocharger. This component pressurises air into the cylinder which goes on to increase oxygen content which results in a better burn. This turbocharging process can increase the power of a diesel vehicle up by 50%, whilst also reducing the engine’s fuel consumption by 25%.
Emission reduction in diesel engines
Since 2015, diesel engines must meet specific standards to ensure minimal impact on the environment. To ensure this specific regulations must be adhered to.
Exhaust Gas Recirculation (EGR)
The EGR system is designed to reduce pollutants, particularly NOx emissions, from the exhaust.
Diesel Oxidation Catalyst (DOC)
The DOC converts unburnt fuel into CO2, preventing hydrocarbons from being released into the atmosphere.
Diesel Particulate Filter (DPF)
The DPF reduces particulate matter (smoke) in the exhaust fumes, ensuring the exhaust gases are as clean and environmentally friendly as possible according to Euro 6 standards.
Selective Catalytic Reduction (SCR)
In modern Euro 6 diesel engines, exhaust fumes pass through the SCR system, where harmful emissions are reduced using diesel exhaust fluid (AUS 32, commonly known as AdBlue). The SCR catalyst combines the exhaust fumes with AdBlue, converting NOx particles into ammonia (NH3) and water, which are then expelled through the exhaust. It is crucial to use AdBlue that meets ISO 22241 standards to prevent potential damage to the engine from contaminants.
Diesel engine maintenance
Diesel engines are known for their durability and long lifespan when properly maintained. To achieve this longevity, regular maintenance is essential, including servicing the engine components, replacing fluids and diesel engine oils that provide lubrication and cooling, and using high-performance fuels.
How far can you drive with petrol in a diesel car?
Driving with petrol in a diesel car can cause serious damage, and how far you can drive before issues arise depends on various factors, such as the amount of petrol added and the type of engine. However, it is generally advised not to drive at all if you realise the mistake.
If a small amount of petrol (less than 5-10% of the tank) has been added, and you start the engine, you might be able to drive a short distance—typically a few miles—before the engine starts showing signs of trouble, such as misfiring, loss of power, or stalling. In more severe cases or with a higher concentration of petrol, damage can occur almost immediately, affecting the fuel pump, injectors, and other engine components.
If you’ve added petrol to a diesel car, it’s best to stop the vehicle immediately, avoid starting the engine, and seek professional help to drain the contaminated fuel and prevent damage.
Manage your company diesel with a fuel card
Fuel Card Services work with major fuel brands to offer you competitive fuel prices that can help to save your business money when it comes to refilling your fleet vehicles with fuel.
To enquire about how these fuel cards could help your business, contact our helpful team today.
back
