Method of lubricating upper cylinder of marine diesel engine

A cylinder lubricating oil composition characterized by having a Total Base Number from about 50 to 100 comprising a mineral lubricating oil, from 10 to 20 percent of an overbased calcium sulfonate and an N-hydroxyethyl alkenylsuccinimide represented by the formula: ##STR1## in which R is a straight chain hydrocarbon radical having form about 8 to 22 carbon atoms.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
Energy costs, particularly as illustrated by the cost of crude oil and 
liquid petroleum distillates derived from crude oil have escalated 
rapidly. These costs are especially burdensome to the users of 
transportation fuels, such as shipowners, and these major consumers of 
petroleum products are reacting to these events and are searching for more 
efficient measures to use in their operations. One significant development 
in the shipping field is the trend away from steam turbine propulsion 
units in favor of large marine diesel engines which are more fuel 
efficient with respect to petroleum fuels. 
The largest marine diesel engines used for ship propulsion are classified 
as slow speed marine diesel engines. These engines are unique both in 
their size and in their method of operation. The engines themselves are 
massive, the larger units approaching 2000 tons in weight and upwards of 
100 feet long and 45 feet in height. Their output can reach 50,000 brake 
horsepower with engine revolutions ranging from about 100 to 125 
revolutions per minute. 
The slow speed marine diesel engines are also unique in their design. Most 
notably, the crankcase of the large slow speed single acting 2-stroke 
crosshead type of engine is completely separate from the combustion 
chambers of the engine. Because of this, its lubrication requirement 
differs from that of a typical diesel engine. In particular, the upper 
cylinder portion of the slow speed diesel engine, not being in direct 
communication with the crankcase zone of the engine, has it own 
lubrication system with specific lubrication requirements that differ 
markedly from the requirements of a crankcase lubricant. In addition, and 
for reasons of economy, the fuel employed to run the large slow speed 
diesel engines are residual fuels having relatively high levels of sulfur. 
This circumstance dictates the employment of a highly overbased 
lubricating oil composition in order to counteract the acidity generated 
during the combustion of the sulfur-containing fuel. As a result, a 
typical cylinder lubricating oil composition for a slow speed marine 
diesel engine will have an alkalinity level expressed as total base number 
ranging between about 50 and 100. 
The fuel consumption rate of a marine diesel engine of 30,000 horsepower 
ranges upwards of 1200 gallons of fuel per hour. In view of the current 
need to reduce overall oil consumption, intensive efforts are being made 
to discover lubricating oil compositions which can materially reduce the 
friction losses which take place within the engine itself. Reductions in 
engine friction losses translate directly into significant fuel savings. 
Numerous means have been employed to reduce the friction in internal 
combustion engines. These range from the use of lower viscosity 
lubricating oils or mixtures of mineral and synthetic lubricating oils as 
well as to the incorporation of friction-reducing additives such as 
graphite, molybdenum compounds and other chemical additives. There are 
limits to the extent to which the viscosity of a lubricating oil can be 
reduced for the purpose of reducing friction. Generally, a lubricating oil 
having too light a viscosity will fail to prevent metal-to-metal contact 
during high load operating conditions with the result that unacceptable 
wear will occur in the engine. With respect to chemical anti-friction 
additives, significant research efforts are ongoing to find effective and 
economic anti-friction additives which exhibit stability over an extended 
service life and under a wide range of operating conditions. 
It is an object of this invention to provide a novel cylinder lubricating 
oil composition for a slow speed marine diesel engine. 
It is another object of this invention to provide a highly overbased marine 
cylinder lubricating oil having improved friction properties for 
lubricating a slow speed marine diesel engine. 
2. Description of the Prior Art 
U.S. Pat. No. 3,779,920 and 4,131,551 disclose overbased calcium sulfonates 
and their use in lubricating oil compositions. 
U.S. Pat. No. 3,879,306 discloses the use of an N-hydroxyethyl succinimide 
as a friction modifier in an automatic transmission fluid. 
The disclosures of all of the U.S. patents noted here are incorporated 
herein by reference. 
SUMMARY OF THE INVENTION 
The cylinder lubricating oil composition of this invention comprises a 
lubricating oil, an overbased calcium sulfonate having a Total Base Number 
from 300 to 450 in an amount sufficient to impart a total base number 
ranging from about 50 to 100 to the lubricating oil composition and a 
minor amount of an N-hydroxyethyl alkenylsuccinimide represented by the 
formula: 
##STR2## 
in which R is a straight chain hydrocarbon radical having from about 8 to 
22 carbon atoms. 
The novel method of the invention involves operating a slow speed marine 
diesel engine by supplying the above-described lubricating oil composition 
to the upper cylinder lubrication system of said engine.

SPECIFIC EMBODIMENTS OF THE INVENTION 
In a more specific embodiment of the invention, the cylinder lubricating 
composition of the invention will comprise at least 80 weight percent of a 
mineral lubricating oil, from about 10 to 20 weight percent of an 
overbased calcium sulfonate sufficient to impart a total base number to 
the lubricating oil composition ranging between about 50 and 100 and a 
minor friction modifying amount of an N-hydroxyethyl alkenylsuccinimide 
represented by the formula: 
##STR3## 
in which R is a straight chain hydrocarbon radical having from about 8 to 
22 carbon atoms. 
A preferred friction modifying component of the lubricating oil composition 
of the invention is one in which R is a straight chain monovalent 
hydrocarbon radical having from about 12 to 18 carbon atoms. A 
particularly effective compound is one in which R has about 12 carbon 
atoms. 
The structure of the alkenyl radical on the N-hydroxyethyl 
alkenylsuccinimide is critical to the performance of the cylinder 
lubricating oil composition of this invention. It is believed that a 
straight chain alkenyl radical on a succinimide is less soluble in the oil 
substrate than a branched-chain radical is and that the reduced solubility 
of the straight-chain hydroxyethyl alkenylsuccinimide causes different 
surface or boundary layer phenomenom that promotes reduced friction in the 
novel cylinder lubricant and method of the invention. 
Methods for preparing hydroxyethyl alkenylsuccinimide are well known in the 
art and do not constitute a part of this invention. 
The friction modifying component of the cylinder lubricating oil 
composition of the invention is effective in a range from about 0.2 to 5 
weight percent based on the total lubricating oil composition. In general, 
it is preferred to employ from about 0.5 to 2 weight percent of the 
prescribed N-hydroxyethyl alkenylsuccinimide with the most preferred 
concentration ranging from about 0.75 to 1.5 weight percent. 
A second essential component of the cylinder lubricating oil composition of 
the invention is an overbased calcium sulfonate having a Total Base Number 
ranging from 300 to 450 on an active material or neat basis. This 
component is employed in the finished cyclinder lubricating oil at a 
concentration ranging from 10 to 20 weight percent based on the weight of 
the lubricating oil composition and sufficient to provide a cylinder 
lubricating oil having a Total Base Number from about 50 to 100. A 
preferred overbased calcium sulfonate has a TBN ranging from about 350 to 
425, a preferred concentration of the sulfonate in the lubricating oil is 
from about 12 to 18 weight percent and a preferred TBN for the lubricating 
oil composition is from 60 to 80. Total Base Number (TBN) is a measure of 
alkalinity determined according to the test procedure outlined in ASTM 
D-664. 
Overbased calcium sulfonates can be derived from sulfonic acids or 
particularly from petroleum sulfonic acids or alkylated benzene sulfonic 
acids. Useful sulfonic acids from which the overbased calcium sulfonates 
are prepared can have from about 12 to 200 carbon atoms per molecule. 
Examples of specific sulfonic acids include mahogany sulfonic acid, 
petrolatum sulfonic acids, aliphatic sulfonic acids and cycloaliphatic 
sulfonic acids. Particularly useful alkylated benzene sulfonic acids 
include polybutylbenzene sulfonic acid, polypropylbenzene sulfonic acid 
and copolymer propyl 1-butylbenzene sulfonic acids having molecular 
weights ranging from about 400 to about 900. 
The overbased calcium sulfonates are produced by neutralizing the sulfonic 
acid with a calcium base to form a calcium sulfonate salt and then 
overbasing the calcium sulfonate with calcium carbonate generally by 
passing carbon dioxide through a mixture of the neutral calcium sulfonate, 
mineral oil, lime and water. Methods for preparing overbased calcium 
sulfonates are disclosed in U.S. Pat. Nos. 3,779,920 and 4,131,551 and the 
disclosures in these references are incorporated herein by reference. 
The hydrocarbon base oil which can be employed to prepare the cylinder 
lubricating oil composition of the invention includes naphthenic base, 
paraffinic base and mixed base mineral oils, lubricating oil derived from 
coal products and synthetic oils, e.g., alkylene polymers such as 
polypropylene and polyisobutylene of a molecular weight of between about 
250 and 2500. Advantageously, a lubricating base oil having a lubricating 
oil viscosity SUS at 100.degree. F. of between about 50 and 1500, 
preferably between about 100 and 1200, are normally employed for the 
lubricant composition. The most preferred lubricating viscosity for a 
cylinder lubricating oil composition is a viscosity ranging from about 68 
to 108 SUS at 210.degree. F. The hydrocarbon oil will generally constitute 
from about 80 to 90 weight percent of the total lubricating oil 
composition with the preferred concentration range being from about 82 to 
about 88 weight percent. 
The improvement in fuel economy brought about by the novel cylinder 
lubricant composition of the invention was demonstrated in the Small 
Engine Friction Test. The Small Engine Friction Test (SEFT) uses a single 
cylinder, air-cooled, 6-horsepower engine driven by an electric motor. The 
engine has a cast-iron block and is fitted with an aluminum piston and 
chrome-plated rings. The electric motor is cradle-mounted so that the 
reaction torque can be measured by a strain arm. The engine is housed in a 
thermally insulated enclosure with an electric heater and is driven at 
2000 rpm. 
Prior to each test, the engine is flushed three times with 1-quart charges 
of test oil. During the test run, the engine and oil temperatures are 
increased continually from ambient until a 280.degree. F. oil temperature 
is reached. The heat comes from engine friction, air compression work and 
from the electric heater. The engine and oil temperatures and the engine 
motoring torque are recorded continually during the test. A SEFT run takes 
about 4 hours. Each test oil evaluation is preceded by a run on a 
reference oil for a like period of time. The torque reference level for 
the engine shifts very slowly with time as a result of engine wear. 
Therefore, the test oil results were recorded compared to a reference band 
consisting of data from up to three reference runs made before and three 
runs made after the test oil evaluation. 
The frictional effects of the novel cylinder lubricating oil composition of 
the invention containing the prescribed N-hydroxyethyl alkenylsuccinimide 
friction modifier was evaluated in a commercial marine cylinder 
lubricating oil composition. The commercial lubricant or base oil and the 
modified oil containing the friction modifier of the invention were tested 
for the friction properties in the Small Engine Friction Test described 
above. The oil compositions and the test results are set forth in the 
table below: 
TABLE I 
______________________________________ 
SMALL ENGINE FRICTION TEST RESULTS 
OF 70 TBN MARINE CYLINDER OIL 
Marine Cylinder 
Modified 
Oil (Base Oil) 
Marine 
L-480-7206.00 
Cylinder Oil 
(Taro Special) 
L-580-7209.00 
______________________________________ 
Composition, Vol. % 
Solvent Neutral Oil - 
38.338 37.338 
SUS at 100.degree. F. of 845 
Bright Stock 145, 
16.300 16.300 
135-145 SUS at 212.degree. F. 
75/80 Pale Oil, 31.550 31.550 
70-77 SUS at 212.degree. F. 
Overbased calcium sul- 
13.800 13.800 
fonate 400 TBN 
Corrosion Inhibitor 
0.012 0.012 
Silicone Antifoamant, ppm 
150 150 
N--(2-hydroxyethyl)-n- 
tetradecenylsuccinimide 
-- 1.000 
100.000 100.000 
Engine Motoring Torque, 
3.20 2.87 
Ft. Lbs. at 280.degree. F. 
Frictional Improvement, % 
-- 10.3 
______________________________________ 
The foregoing example demonstrates the realization of a 10.3 percent 
reduction in the frictional properties of a 70 TBN marine cylinder oil due 
to the presence of an N-(2-hydroxyethyl) alkenylsuccinimide friction 
modifier. This invention provides an unexpected improvement in the 
frictional properties of a highly overbased marine cylinder lubricating 
oil composition for a large slow speed diesel engine.