Base oil – the foundation of the finished oil, one of its main components. It has the greatest influence on the properties of the final product. The base oil determines “how synthetic” the product will be. Base oils are divided into five groups: mineral, semi‑synthetic, hydrocracked, PAO‑synthetic and “non‑petroleum” synthetic.
Direct injection – an electronic fuel delivery system for gasoline engines, structurally very similar to the Common Rail system in diesel engines. In direct‑injection systems, fuel, unlike a “conventional injector”, is injected not into the intake manifold where it mixes with air and passes through the intake valve into the combustion chamber, but directly into the engine cylinders at very high pressure. This allows layered mixture formation already inside the combustion chamber and layered and multi‑stage combustion of the air‑fuel mixture, which, with precise engine control system tuning, ensures more complete fuel combustion, reduced harmful emissions, and improved fuel economy of the engine.
Volatility – one of the oil characteristics that affects its consumption. Oil, like any liquid, evaporates over time. The standard volatility for automotive engine oils is 15%. At the same time, the volatility of high‑grade motorcycle oils is regulated at 6%.
Volatility also indirectly indicates the quality of the base oil used.
Viscosity – one of the basic oil property characteristics, defining its flowability. Oil viscosity is divided into kinematic and dynamic (HTHS).
Kinematic viscosity determines the actual flowability of the oil, its thickness, and, according to SAE J300 specification, is divided into “cold” (winter) and “hot” (at 100 °C). Depending on the actual properties of the oil, it is assigned one of the viscosity grades. Each viscosity grade corresponds to a specific range of actual oil viscosity values.
Dynamic viscosity (HTHS) determines the stability of the oil film and its density in a dynamic environment. The abbreviation HTHS fully describes the conditions under which the measurement is performed – high temperature at high shear rate (High Temperature High Shear). Physically it is the product of kinematic viscosity and its density, measured in centipoise (cP).
Based on the dynamic viscosity parameter, oils are commonly divided into two classes: high‑viscosity oils with HTHS > 3.5 (the so‑called standard HTHS viscosity) and low‑viscosity oils with HTHS < 3.5. It should be noted that using oils with low dynamic viscosity (reduced HTHS) in engines designed for such oils does not cause additional wear. However, using high‑viscosity oils in such engines, while not causing extra wear, generally leads to reduced power and fuel efficiency, and adversely affects hydraulic lifters, variable valve timing systems (VVT‑I, VTC, CVVT).
In recent years there has been a gradual shift by all manufacturers toward using low‑viscosity oils in new engine models.
Sulfated ash content – one of the parameters that characterizes the detergent‑dispersant properties of oil, its ability to neutralize acids formed during fuel combustion, to keep insoluble combustion products in suspension, and to prevent their precipitation and deposition on engine components as high‑ and low‑temperature deposits.
When using fuel with a high sulfur content, increased ash and the oil’s alkalinity prevent deposit formation. However, excessively high ash content leads to increased engine wear due to abrasive action on friction pairs, formation of ash deposits in the combustion chamber, reduced fuel detonation resistance, and premature failure of exhaust gas recirculation systems and particulate filters.
Based on sulfated ash content, engine oils are classified as high‑ash (ash content 0.8‑1.5%) and low‑ash (ash content < 0.8%). An unofficial class is the so‑called medium‑ash oils with sulfated ash content 1.0‑1.2%.
Viscosity index (viscosity index) is a dimensionless value that reflects the temperature stability of oil properties. The higher it is, the more stable the oil’s viscosity characteristics are with temperature changes.
(viscosity grade) – conditional designation of the oil’s property complex, the main one being its kinematic viscosity. According to the SAE J300 standard, engine oils are divided into 13 viscosity classes from 0W to 60, and transmission oils – from 70W to 140. When indicating kinematic viscosity, the “cold” viscosity is listed first (SAE 0W, 5W, 10W, 75W, 80W, etc., where “W” stands for winter), followed by the “hot” (SAE 20, 30, 40, 90, etc.). All‑season oils are marked with two indices (5W30, 5W40, 10W40, etc.). The lower the oil’s viscosity class, the lower its corresponding viscosity. The primary parameter for determining cold viscosity is its pumpability and flowability. The hot viscosity of the oil is determined at 100 °C.Alkalinity number (TBN) – one of the oil’s characteristics that indirectly indicates its cleaning properties. During fuel combustion in the engine, acids are formed, which cause corrosive wear and carbon deposits. To neutralize them, a base is used, the amount of which in the oil is expressed by the alkalinity number. The lower the fuel quality, the higher the required alkalinity number of the engine oil.
The alkalinity number of heavy‑duty oils can reach 15 mg KOH/g or more, while in fuel‑efficient passenger car oils the value is limited to 6 mg KOH/g.
Pump‑injector (Pumpe‑Düse, PD) – an electronic diesel engine fueling system developed by Volkswagen AG. It is a system in which a high‑pressure fuel pump and injector are mechanically combined in a single unit. Thus, the fuel injector also serves as its own pump. The system was used in the 2000s on vehicles of all brands within the group, but due to lower reliability and high maintenance cost it was later replaced by Common Rail.
Additives – additional components to the base oil that improve, complement its characteristics or give it extra properties. A balanced, verified additive package is part of any modern oil – engine, transmission, hydraulic, industrial.
A chemically and physically verified package represents a set of additives that endows the finished oil with a specific set of properties.
Oil flowability (Low Temperature Cranking Viscosity) – an additional parameter characterizing the oil’s low‑temperature properties, indicating the ability to turn the engine’s crankshaft. The actual value is determined by the ASTM D5293 test method. Due to the non‑linearity of oil temperature properties, pumpability is defined by oil characteristics, while flowability is determined at various sub‑zero temperatures for different viscosity classes. The lower this parameter, the better the oil’s low‑temperature performance.
Oil pumpability (Low Temperature Pumping Viscosity) – one of the key parameters of the oil’s low‑temperature properties. The actual pumpability is determined by the ASTM D4684 test method and indicates the minimum temperature at which the oil’s viscosity does not exceed 60 000 mPa·s. Pumpability is tested after conditioning at the appropriate viscosity class at a sub‑zero temperature for 45 hours. The lower this parameter, the better the oil’s low‑temperature performance.
Diesel particulate filter
Flash point (flashpoint) – a key parameter characterizing oil consumption due to oxidation. During engine operation, oil vapors that can ignite when mixed with air are formed. The higher the oil’s flash point, the higher the temperature at which its vapors ignite, and the lower the oil’s oxidation loss under standard engine operating conditions. Lower oil oxidation, in turn, reduces the amount of carbon buildup in the engine. The flash point also indirectly indicates the quality and class of the base oils and additive packages used.
Pour point (pour point) – one of the main parameters characterizing the oil’s low‑temperature properties. It defines the temperature at which engine oil transitions from a liquid to a gel‑like state and begins to crystallize. The lower the pour point, the lower the temperature at which the engine can be started without critical wear.
AdBlue – the working fluid of the Selective Catalytic Reduction (SCR) exhaust gas treatment system. It is a 32 % aqueous urea solution. The fluid is highly sensitive to storage and operating temperature conditions and to the quality of water used to prepare the solution. Using fluid that has been exposed to temperatures outside its specified limits can lead to reduced engine efficiency, increased fuel consumption, and mechanical failures.
– electronic fuel injection system for diesel engines, developed by Bosch. Structurally very similar to the direct injection system in gasoline engines. In a Common Rail system all fuel injectors are connected to a single (or two in some V‑shaped engines) fuel rail, the pressure in which is maintained by a high‑pressure fuel pump (HPFP). The injectors are controlled by the electronic engine control unit. It is the most widespread diesel engine fueling system today.
DPF (diesel particulate filter) – a filter for solid particles installed in the exhaust system of modern diesel engines of passenger and commercial vehicles. It reduces exhaust toxicity by capturing solid combustion products of diesel fuel, soot. Visually similar to a catalyst, but larger in size. On some vehicles it is structurally combined as a single component with the catalyst. It is demanding on the engine oil used – it must have reduced ash content (ACEA C3, C4, ILSAC etc.)
EGR (exhaust gas recirculation) – a system for recirculating and reburning exhaust gases of gasoline and diesel engines. It consists of a valve that connects the exhaust tract with the post‑combustion space of the intake tract. It is one of the most effective ways to reduce exhaust toxicity. Returning a portion of the spent gases to the intake manifold lowers the peak combustion temperature of the air‑fuel mixture and reduces the intensity of nitrogen oxide formation. The operation of the system slightly reduces the engine’s effective power. The system operates under partial load conditions and does not engage at idle, on a cold engine, or with the throttle fully open. EGR is not used on turbocharged gasoline engines.
HTHS – see Dynamic Viscosity
Pumpe-Düse – see Pump‑Injector
TBN – see Alkaline Number
SCR (selective catalytic reduction) – a system for selective catalytic neutralization of diesel engine exhaust gases. The SCR principle is based on the chemical conversion of exhaust gases into harmless substances – water and nitrogen. The system injects the active substance (catalyst) AdBlue directly into the vehicle’s exhaust tract, where a chemical reaction occurs. In addition, using the SCR system can reduce fuel consumption by 3‑5%, which is especially noticeable on heavy trucks and long‑haul tractors. The consumption of the active substance amounts to 4‑5% of the fuel volume consumed.
The chemical reaction in the SCR system proceeds in two main stages.
In the first stage the AdBlue solution is injected into the hot exhaust gases, where a hydrolysis process forms ammonia: (NH2)2CO + H2O => 2 NH3 + CO2
During the second stage decomposition into nitrogen and water occurs:
4NH3 + 4NO + O2 => 4 N2 + 6H2O
8NH3 + 6NO2 => 7N2 + 12H2O
