DIESEL ENGINE LUBRICANTS

Abstract

Diesel engine lubricants consist of base oil, a viscosity modifier, and an additive package. This may include antioxidants or pour point depressants, as well as detergents and dispersants. Its most important property is its viscosity. It is important to choose the right oil viscosity in order to ensure hydrodynamic lubrication occurs where it is needed. Oil can be contaminated by unburned fuel, soot, and metallic particles. An oil analysis is a common method to determine the appropriate oil drain intervals.

Lubricant Formulation

Overview

The diesel engine’s lubricating oils play a variety of crucial functions:

• Wear reduction of components, such as bearings and pistons, piston rings, cylinder liner, and the valve train
• Hydrodynamically and boundary lubricated parts are less likely to friction.
• Piston cooling
• Acids and moisture can prevent corrosion
• Cleansing pistons and preventing sludge buildup on internal surfaces
• To prevent seal failure, keep seals lubricated. Control swelling.
• As a hydraulic media in components like the HEUI fuel system.

Base oil is typically 75-83 percent, viscosity modifier (5-8%), and an additive package (12-18%).  The additive package is an important part of oil formulation because the base oil cannot provide all the necessary lubricating oil functions for modern engines.

Base Oil

The base oil can be made up of either a mixture of several base stocks or one base stock. You can make base stocks from petroleum feedstock using many different methods, including solvent refining and hydrogen processing. The Fischer-Tropsch process is also used to synthesize high-quality base stocks from feedstocks such as natural gas (GTL). Bio-synthesis Can also be used for base stocks made from renewable feedstocks such as plant sugar [Vettel 2012]. You can also recover base stocks from used oil recycling.

The American Petroleum Institute (API), which classifies engine lubricants that are licensed to have an API classification symbol, divides them into different categories. In Europe, the Association Technique de L’Industrie Europeenne des Lubrifiants (ATIEL) defines base oil groups for use in ACEA oil sequences. The ATIEL Groups I to V are identical to API. However, ATIEL added a Group VI between 2003 and 2010.

Base stocks of Group I are low in saturates and/or high levels of sulfur. Groups II and III have high saturates but low levels of sulfur. Polyalphaolefins are used to make synthetic oils in Group IV base stock. Finally, Group V base stock is synthetic oils that do not belong to Groups I-IV. Marketers sometimes refer to Group I and Group II base stock with a viscosity index higher than 110 as Group I+ or Group II+ base stock, respectively. These products are also differentiated by the increased use of Group III base oils. The distinction is not as clear. Base oils belonging to Group III+ can be used depending on their viscosity index.

Base stocks of Group I are the lowest quality. These base stocks are made by physically separating lubricant molecules by solvent refining. This is a two-step process that involves the partial removal of aromatics with solvent and then the subsequent removal of wax by precipitation using a different solvent. These unaudited Group I base stocks may still contain more aromatics than 10%. This makes them susceptible to oxidation and gives them poor viscosity. So that Group I base stocks perform well, special crude oils must be used that contain the required lubricant base oil molecular compounds.

A variety of hydroprocessing technologies are used to make Group II base stock. Hydrotreating is an additional step in retrofitting or hybrid Group II plants. This allows for greater flexibility in crude oil selection than Group I base stock. Catalytic processes convert non lubricant molecules to lubricant molecules in a Group II hydrocracking facility. This allows for greater feedstock flexibility and lower-quality/lower-cost crude oils. The Group II base stock manufacturing process can remove significant amounts of nitrogen- and sulfur-containing compounds as well as aromatics. This makes Group II base stocks superior to Group I. Group II base stocks are less likely to form oxidation products and are, therefore, more inert. Group II base stock molecules are less dependent on crude oil sources because they are cracked and reshaped.

Group III base stock is made in the same manner as Group II but at higher temperatures and longer residence times in reactors. They have much better temperature characteristics. Group III includes gas-to-liquid (GTL) derived base stock. Bio-synthesis of Group III+ base stock can be done.

The increased demand for fuel economy and emissions reductions in automotive applications has resulted in a decrease in Group I base stock usage and an increase in the use of Group II, and I base stock. These higher-quality base stocks have opened up new uses for Group II base stock beyond the original need for automotive lubricants. Switching to marine trunk piston engine lubricants made from Group II base stock can reduce maintenance costs and operating expenses.

Group IV base stocks have been traditionally referred to as “synthetic” or “synthetic” in their original form. These polyalphaolefins are made from smaller molecules. They were one of the most efficient base stocks at the time they were introduced. Manufacturers began using high-viscosity index feedstocks in order to produce mineral oils that were comparable to PAOs’ performance. These Group III base stocks matched the performance and cost of PAOs, but at a lower price. Group III base stocks in North America can also be called “synthetic.”. Also, biosynthesized PAO base stocks have been created. Combining low-viscosity PAOs with Group III base stock offers a way to create low-viscosity engine oil formulations that improve fuel economy and maintain acceptable oil volatility characteristics.

Polyalkylene glycols, alkylated naphthenes (AN), and esters such as polyol esters, pentaerythritol esters, trimethylolpropane esters, and aromatic esters (phthalates or trimellitates) are all part of Group V base stock. There are still new ones being developed, including oil-miscible liquid ionic fluids. [Qu 2011]. These synthetic base stocks can be attractive for specific applications because of their many properties.

• Polar base stocks can enhance the properties of traditional additives and reduce the need for additives.
• Higher thermal stability can increase the operating temperature range by up to 50-100degC
• In some cases, increased film strength and lubricity may reduce energy consumption.
• Some are biodegradable, and others have low environmental toxicity.