After completion of this module you will be able to:
12
Diesel Technology
• Understand fundamental diesel principles
• Understand the fundamental differences between gasoline and diesel engines
• Understand the required service procedures on diesel engines
• Understand diesel fuel injection and engine management systems
• Understand diesel exhaust emissions and emission control systems
BMW Diesel Technology
For the first time since 1986, BMW will have a “Diesel powered”
vehicle in U.S. market. The previous diesel engine in use was the
M21D24. The M21 was only available in the 524td (E28).
This engine featured state of the art technology which included
turbocharging and the latest Bosch diesel fuel injection. At the
time, the M21 was considered to be one of the best performing
turbo diesel engines in the world.
However, diesel engines were not widely accepted in the U.S.
market. This was due to the relatively cheap prices of gasoline
and the negative perceptions associated with diesel engines.
Most of the available diesel engines available in the market at the
time were not very appealing to the average customer. Engine
noise, fuel and exhaust odors along with soot emissions contributed to a negative image of diesel engines. Also, diesel
engines were somewhat sluggish as compared to their gasoline
fueled counterparts.
One of the positive attributes of diesel engines was fuel economy
and overall efficiency. This was one area in which the diesel
engine excelled.
Even with all of the positive aspects of diesel ownership
evident, most customers did not widely embrace the diesel
experience. As a result, the 524td was discontinued in 1986.
However, since 1986, BMW continued to refine and develop
diesel engines for other markets. The high price of available fuel
in other countries drove customers to diesels at a higher rate than
in the U.S. market.
To meet the demand for diesel engines, BMW improved on the
6-cylinder diesel engine. In addition to the 6-cylinder, 4 and 8
cylinder diesels were developed for other markets.
Over the last 20 years, BMW has continued to improve on the
diesel engine and reduce the “undesirable” aspects of diesel
ownership. Power output has been increased, while reducing
noise and emissions. In European markets, diesel vehicles now
account for more than 50% of newly registered vehicles. Sales of
BMW diesel vehicles account for more than 60% of new vehicle
purchases in the European markets.
In the fall of 2008, BMW will re-introduce diesel vehicles to the US
market in the form of a 6-cylinder, twin turbo engine featuring the
latest in common rail fuel injection technology.
The new engine will be referred to as the M57TU2 TOP. The new
6-cylinder diesel engine from BMW will offer the same high level
of performance that is expected from BMW drivers.
In short, the new diesel vehicles will fit well into the concept of
“Efficient Dynamics”. This concept ensures the highest reduction
in CO
emissions without a compromise in performance.
2
The new diesel BMW’s offer two features which, together, are not
usually associated with diesel engines or spoken in the same
sentence - Performance and Efficiency.
Diesel Technology
13
14
$3.33$6.31
U.S. Average Price
for Diesel Fuel
(winter 2010)
European Average
Price for Diesel Fuel
(winter 2010)
Diesel Technology
Why did the diesels disappear from the US Market?
In the US market, diesel vehicles have not had much success over
the last 20 years. Most of this is due to customer perception and
the relatively low cost of gasoline.
Although many people feel that the price of gasoline is high in the
US, other parts of the world pay much higher prices due to the
additional taxes. In comparison, fuel prices in Europe are twice as
high as in the US. This accounts for the difference in the overall
acceptance of diesel between the US and European markets.
In the early 1980’s the price of gasoline was increasing, but was
not enough of a motivating factor to convert customers to diesel
vehicles in sufficient numbers. Diesel engines did not offer enough
of an alternative to gasoline engines because they did not perform
as well. They were sluggish and did not deliver much in the way of
dynamic performance.
Customer Perception
More than 20 years ago, the diesel vehicles available in the US
market did not have the advantages of today's technology. By the
time BMW brought the 524td to the US, the diesel market had
already declined due to the less than desirable aspects of some of
the competitive products available at the time.
Much of the negative perception of diesel vehicles centered around
the odors from the exhaust and fuel itself. Also, diesel exhaust
contained a high amount of soot which contributed to the dirty
image of diesel vehicles.
The combustion process in early diesel engines was abrupt and
created a lot of additional engine noise as well. This noise gave the
diesel passenger car more of a “truck-like” impression to potential
customers.
Summary
The absence of diesel powered passenger cars in the US can be
summed up in the following areas:
• Engine noise
• Exhaust odors
• Dirty, soot emissions excessive
• Fuel smell
• Low power, lack of performance, sluggish
• Cold starting performance
• High emissions of NO
X
The above mentioned issues on the diesel engine have been
resolved with the advancements in engine, emissions and fuel
injection technology. In the subsequent pages, the latest diesel
technology will be reviewed and explained in more detail.
Why are diesels making a comeback in the US?
Given the current global concerns, BMW diesel engines are a
logical choice for customers looking for economy and performance.
There are other alternatively fueled vehicles on the market today,
but BMW offers a true “premium” experience with the diesel
engine.
Everyday, the news is filled with articles on global warming and the
need for a reduction in CO
discussions on the need to reduce our dependence on foreign oil
and to look for alternatives.
emissions. There are continuing
2
have kept customers from experiencing diesel technology.
The lack of available diesel vehicles in the US has only served to
keep interest at a minimum.
Today, more and more customers are becoming aware of diesels
and the potential benefits of ownership. BMW offers all of these
benefits with the addition of performance and the usual value that
customers expect.
The new BMW engines benefit from the latest “common rail” fuel
injection systems. These systems are high pressure, precision
injection systems which are capable of having multiple injection
events. These systems contribute to the increased performance
and reduction of emissions.
As compared to the M21 engine from 1983, the latest BMW diesel
vehicles have improved in the following areas:
• Engine noise has been reduced by engine design and fuel
injection strategy. Additional engine soundproofing also
contributes to the reduction in noise.
• Particulate emissions have also been reduced by 99% as
compared to the M21 engine. This was accomplished by
injection strategy and by the new diesel particulate filter (DPF).
BMW is offering alternatives in the form of Hydrogen power, future
Hybrid technology and now “Diesel Power” for the Ultimate Driving
Machine.
In the last 20 years, BMW has developed “cutting edge” diesel
engines which have gone relatively unnoticed in the US market.
This is due, primarily, to the perception of the customer.
Past negative experiences or a lack of overall diesel knowledge
Diesel Technology
• Fuel consumption has been reduced by 20%.
• Torque output has been increased by 160% through the use
of the innovative twin-turbocharger design.
• Horsepower has been increased by more than 135%.
• NO
is further reduced by the diesel oxidation catalyst, EGR
X
valve and by the new SCR system.
• Other engine modifications also contribute greatly to the
modern BMW diesel engine.
In short, it’s time to bring the diesel back.
15
16
Diesel Technology
Efficient Dynamics
Today, much of the focus from the automotive industry centers
around fuel efficiency and concern for the environment through the
reduction in CO
“dynamic” are not usually adjectives used to describe the same
vehicle. However, this is not the case when describing vehicles
from BMW.
output. Usually, the words “efficient” and
2
One of the first vehicles to be associated with the “Efficient
Dynamics strategy was the BMW Hydrogen 7. This vehicle is also
the flagship for BMW’s “Clean Energy” concepts. The new BMW
Hydrogen 7-series is “bivalent” which means it can be run on both
gasoline and hydrogen.
The “Hydrogen 7” has a V-12 internal combustion engine which
takes advantage of one of the most plentiful and “eco-friendly”
resources on Earth - Hydrogen. Using hydrogen as an automotive
fuel is not an entirely new concept for BMW. These ideas have
been in development by BMW since the 1970’s.
It’s important to note, that the new Hydrogen 7 is not only a
concept vehicle, but is a production vehicle which is currently for
sale. Although it is not currently available in the US, is being tested
here and will be for sale in other markets.
Many of our customers are familiar with our most famous tag line
“The Ultimate Driving Machine” and they won’t settle for anything
less. It is a huge challenge to not only meet performance expectations, but to maintain overall efficiency and environmental responsibility.
BMW has been able to meet and exceed these goals through the
latest innovations in engine technology. Systems such as VANOS,
Valvetronic, lightweight engine construction and the latest in engine
management have contributed to increasing performance while
improving fuel economy.
BMW’s dedication to Efficient Dynamics does not rest on a single
vehicle, but rather is evident on many other new products and
technologies.
For example, BMW gasoline engines have had many fuel saving
innovations for many years. Recently, Valvetronic technology has
allowed BMW vehicles to gain “best-in-class” fuel economy across
the model line.
To complement all of the engine technology currently in use, BMW
will be adding diesel powered BMW’s to the model line by the end
of 2008. Besides the obvious fuel saving advantages of diesel
engines, there are many performance related aspects of this new
technology.
The new 335d for the U.S. market is expected to accelerate from
0-62 mph in 6.2 seconds while achieving a fuel economy of 23/36
mpg (city/highway provisional data). The same engine in the X5
can accelerate to 62 mph in 7.2 seconds while offering fuel economy figures of 19/26 mpg (city/highway provisional data).
With its carbon emissions down 10% - 20% from comparable
gasoline vehicles, and near-elimination of both smoke and NOx
emissions, BMW Advanced Diesels will be every bit as clean as
CARB-legal gasoline engines when they are introduced in the US
in 2008.
Some of the other engine innovations include high-precision direct
fuel injection for gasoline engines. The HPI system allows the N54
engine to maintain maximum performance and astounding fuel
economy in a 300 hp engine.
Diesel Technology
Both diesel and gasoline engines from BMW have taken home the
prestigious “International Engine of the Year Award” several times.
Now, one of these award-winning diesel engines will be available
in 2009 models.
17
18
Diesel Technology
New Diesel Engine
Some of the features on the M57TU2 TOP include:
• A horsepower rating of 265 hp
• 425 lb-ft (580 Nm) of torque
• 3rd Generation common rail fuel injection (1600 bar) with
Direct Injection
• Piezo-electric injectors
• Two-stage turbocharging with intercooler
• Lightweight aluminum alloy crankcase
• Particulate filter (DPF)
• EGR system with EGR cooler
• Diesel Oxidation Catalyst
• Digital Diesel Electronic (DDE)
• Selective Catalytic Reduction (SCR) System
Engine Specifications
In addition to the features listed above, the new 6-cylinder diesel
includes fuel heating system and a new “fast start” glow plug
system to ensure optimum cold weather starting.
Note: In accordance with the current engine numbering
system, the M57TU2 TOP engine will be known
officially as the M57D30T2.
M57TU2 TOP/M57D30T2
Number of Cylinders6
Bore84
Stroke90
Displacement2993 cm3
Compression Ratio16.5:1
Compression pressure> 12 bar
Maximum RPM5250
Maximum continuous RPM4400
U.S. Diesel Specifications
U.S. Market Diesel Introduction
Beginning with model year 2009, BMW will introduce 2 diesel
models for the first time since 1987. The E90 and E70 will be
available with the new M57D30T2 (US) engine.
In addition to having a new engine, the new diesel powered
3-series will also be considered a “face-lifted” version (or LCI)
with other changes to be detailed in future training.
The two new models will meet the EPA Tier 2, Bin 5 requirements
and will be considered “50 State” legal. In order to comply with
these new stringent regulations, both vehicles have the latest in
emission control and engine management technology.
Both vehicles will be equipped with the latest Selective Catalytic
Reduction system to reduce unwanted NOxemissions. Also, the
X5 will have an additional Low Pressure EGR system to further
assist in the reduction of NOx.
The E90 will be known as the 335d, while the E70 will reflect the
new naming strategy as the X5 “xDrive35d”.
Diesel Technology
The new X5 xDrive35d and 335d will be available in the late fall
of 2008 with the same impressive six-cylinder diesel engine.
The provisional fuel economy data is as follows:
• 23/36 mpg (city/hwy) for the 335d
• 19/26 mpg (city/hwy) for the X5 (X Drive 35d)
Note: The above fuel economy data is provisional.
The official EPA data is not currently available.
19
20
Diesel Technology
A Diesel Engine for North America
Impressive power and performance as well as exemplary efficiency
have contributed to making BMW diesel engines an attractive as
well as future-oriented drive technology.
This technology is now being made available to drivers in North
America. BMW is introducing this diesel technology to the USA
and Canada under the name "BMW Advanced Diesel with Blue
Performance".
In the 2008 International Engine of the Year Awards, the BMW
diesel came in second in the 2.5 to 3.0 liter category. Surprisingly,
the M57D30T2 engine finished second only to the gasoline
powered N54 engine.
But, both the N54 and M57 diesel engines finished well ahead of
the competition which included diesel engines from other manufacturers.
The introduction is an integral part of the Efficient Dynamics
development strategy, which has become a synonym for extremely
low CO2emissions - not surprising when considering its extremely
low fuel consumption.
Efficient Dynamics is not solely an instrument for reducing fuel
consumption, but rather it is designed as an intelligent entity with
increased dynamics. Not without good reason, the M57D30T2
engine is referred to as the world's most agile diesel engine.
The following pages contain a comparison of the new BMW diesel
engine technology to the current BMW gasoline engine technology.
The following full load diagrams provide a comparison of the new
diesel engine to the current production gasoline engines, both 6
and 8 cylinder.
Most notably, the diesel has the advantage in the torque output.
The above comparison shows a comparison between the N52
engine, which is a naturally aspirated 3-liter gasoline engine.
The power developed by the gasoline engine is carried over a
broader RPM range, but the diesel has more output torque which is
available at a much lower engine speed.
In the above graph, the N54 has a slight advantage in peak output
with regard to horsepower. Since the N54 is a turbocharged
engine, the output torque figures show the torque output at a lower
engine speed, but it is quite “flat” up to almost 5000 RPM.
In contrast, the diesel has a much higher torque output, but is only
available for a short time. After about 2400 RPM, the torque drops
off considerably.
Nm
lbft
600
443
268
200
560
413
241
180
520
384
215
160
480
354
188
140
440
325
161
120
400
295
134
100
360
265
107
80
320
236
80
60
280
207
54
40
240
177
27
20
200
148
0
0
349
260
322
240
295
220
hp
kW
1000200030004000500070006000
M57D30T2 (335d, X5 XDrive35d)N62B48O1 (X5 4.8i)
n [1/min]
TD08-1380
Diesel vs. N62
NOTES
The familiar N62B48O1 has impressive horsepower output but,
even with 8-cylinders, it does not have the torque output of the
M57 diesel engine.
Overall, these engine output graphs illustrate that the diesel has
very specific characteristics especially with regard to torque output.
Vehicles with diesel engines are adapted to suit these torque
characteristics with an upgraded torque converter and a rear axle
gear ratio which allows the full utilization of the output curve.
In short, the new BMW diesel engine exceeds all of the currently
available gasoline engines up to an engine speed of about 4000
rpm.
PAGE
Diesel Technology
23
Diesel Fundamental Principles
24
Diesel Technology
First and foremost, a diesel engine operates on the “compression
ignition” principle. A compression ignition engine begins the
combustion cycle without the need for an external ignition system.
What makes a diesel engine attractive to potential customers is
that it is much more efficient than a gasoline engine. This is due
to several factors:
• Diesel engines run at a much higher compression ratio
• The energy density of diesel fuel is much higher than an
equivalent amount of gasoline
• Overall, diesel engines are more thermally efficient than
gasoline engines
• Diesel engines are run very lean (with excess air)
• Diesel engines operate with the throttle in the open position
which reduces pumping losses
In order to ignite fuel without a spark, the compression ratio must
be relatively high. The compression ratio on most gasoline
engines ranges from 8:1 up to as high as 12:1. On the other
hand, compression ratios on diesel engines range from 16:1 up to
about 22:1 for most passenger car engines.
A higher mean pressure value in combination with the higher
energy density of diesel fuel translates to more pressure during
combustion. This higher combustion pressure is responsible for
much higher output torque. This additional torque is available at a
relatively low RPM as compared to a gasoline engine.
The load control of a diesel engine is not carried out by regulating
the amount of air as on a gasoline engine. Rather, the diesel
engine is “throttled” by the amount of fuel injected. This type of
load control means that the throttle butterfly is mostly open during
all engine phases.
Since the throttle is always open, there is always more than
enough oxygen available to burn all of the fuel injected. This
allows then engine to operate in a very lean state which also
contributes to increased efficiency of the diesel engine.
In comparison, gasoline engines must run at a lambda value as
close to 1 as possible. A diesel engine can operate at lambda
level of 1 to 2 under load and up to 10 when at idle or under low
load conditions.
An added benefit of having the throttle open during most phases
of engine operation is the reduction of pumping losses. This has
the same beneficial effect that Valvetronic has on a gasoline
engine.
A direct benefit of a higher compression ratio is increased thermal
efficiency. In comparison to a gasoline engine of comparable
displacement, modern diesel engines generate more cylinder
pressure during the compression phase. The average “mean
cylinder pressure” value of a turbocharged diesel engine is from
8 to 22 bar, while a comparable turbocharged gasoline engine is
only about 11 to 15 bar.
In summary, early diesel engine designs were already much more
efficient than the prevailing gasoline engine technology. However,
fairly recent developments in engine and fuel injection technology
have contributed to major advances in the success of the diesel
engine.
In particular, modern BMW “Performance Diesel” engines provide
and
the added bonus of economy
proven diesel engine has been enhanced and optimized to fulfill
the brand promise of “The Ultimate Driving Machine”.
performance. The already
Diesel Engine to Gasoline Engine Comparison
In order for the diesel engine to start it’s combustion cycle, fuel must be ignited by the heat of compression. The fuel used must be able
to spontaneously ignite (without the help of a spark from an external ignition source). So, the fuel required for a diesel engine must have
special properties to be compatible with proper engine operation. The best way to illustrate this is to compare both engines and the fuel
used.
The following is a comparison of a gasoline engine as compared to a diesel engine:
SpecificationGasoline Engine (Otto)Diesel Engine
Ignition Type
Compression Ratio
Efficiency
Maximum Engine Speed
Exhaust Temperature
(under full load)
Fuel Type
Fuel Density
Flash Point
Spark IgnitionCompression Ignition
Between 8:1 and 12:1Between 16:1 and 22:1
25-30%36-45%
7000-8250 RPMup to 5250 RPM
700-1200 Degrees Celsius300-900 Degree Celsius
Gasoline
(Octane rating = resistance to knock)
0.74 - 0.770.82 - 0.85
-47 Degrees Celsius
(-52.6 Degrees Fahrenheit)
(Cetane rating = ability to ignite)
(131 Degrees Fahrenheit)
Diesel
55 Degrees Celsius
Ignition Temperature
550 Degrees Celsius
(1022 Degrees Fahrenheit)
Diesel Technology
25
350 Degrees Celsius
(662 Degrees Fahrenheit)
26
Diesel Technology
Combustion Cycle Comparison
Much like a gasoline engine, the diesel engine uses the 4-stroke cycle. The familiar sequence of; Intake > Compression > Power and
Exhaust is much the same on a diesel engine. The difference is mostly in how the fuel is ignited and when fuel is introduced into the
combustion chamber.
The other area in which diesel engines differ is in the compression ratio. The typical gasoline engine has compression ratios of between
8:1 up to about 12:1. On the other hand, diesel engines have a typical compression ratio of between 16:1 and 22:1. The higher
compression ratio is required to sufficiently compress the air charge and raise the temperature to the ignition point.
The illustrations below show the sequence of the combustion cycle on a conventional
Intake Stroke
Gasoline Engine
A low pressure area is created as
the piston moves downward in
the cylinder bore.
As the intake valve opens, a
mixture of air and fuel is allowed
to enter the cylinder to fill the
void created by the low pressure
area.
Compression Stroke
Gasoline Engine
As the piston moves up in the
cylinder, both valves are closed.
The mixture of air and fuel is
compressed to a specific ratio.
Power Stroke
Gasoline Engine
The compressed air and fuel
mixture is ignited by a spark from
the ignition system.
The piston is forced down in the
cylinder by the expanding gases.
This creates the necessary force
to drive the crankshaft.
gasoline
engine with “manifold injection”.
Exhaust Stroke
Gasoline Engine
The exhaust valve opens as the
piston moves up in the cylinder
which expels the spent gases
formed during the combustion
process.
Note:
A gasoline direct injection engine
would only induct air during this
period.
Note:
A gasoline direct injection engine
would only compress air during
this period.
Note:
A gasoline direct injection engine
would inject fuel and ignite it with
a spark during this period.
Note:
A gasoline direct injection engine
would operate the same during
this period.
Diesel Combustion Cycle
In the example above, the combustion cycle on the gasoline engine was discussed. In contrast, the sequence below outlines the
combustion cycle on the diesel engine. This will help in the understanding of the diesel/gasoline engine comparison.
Intake Stroke
Diesel Engine
A low pressure area is created as
the piston moves downward in
the cylinder bore.
As the intake valve opens, air is
allowed to enter the cylinder to fill
the void created by the low
pressure area.
Note:
The recess in the piston and the
design of the intake manifold
assist in creating a “swirl effect”
for the incoming air.
Compression Stroke
Diesel Engine
As the piston moves up in the
cylinder, both valves are closed.
The air is compressed to a high
ratio and therefore heated to a
high temperature in preparation
for the incoming fuel.
Note:
Only air is compressed during
this period.
Power Stroke
Diesel Engine
Just before the piston reaches
TDC, fuel is injected at high
pressure directly into the combustion chamber.
The fuel spontaneously ignites
and pushes the piston down in
the cylinder.
This creates the necessary force
to drive the crankshaft.
Note:
Fuel is injected for a longer time
during this period. This feature
contributes to the additional
torque generated by a diesel
engine.
Exhaust Stroke
Diesel Engine
The exhaust valve opens as the
piston moves up in the cylinder
which expels the spent gases
formed during the combustion
process.
Note:
Due to the higher thermal
efficiency of a diesel engine, the
exhaust temperature is lower as
compared to a gasoline engine.
Diesel Technology
27
GasolineDiesel
28
Diesel Technology
Diesel Fuel Properties
Before discussing diesel fuel injection or fuel systems, it is necessary to explain the properties of diesel fuel and how it differs from
gasoline. Although both fuels are distilled from crude oil, they each have their own uses and applications and should never be
interchanged.
Gasoline
The BTU value for gasoline
is approximately 125,000
BTU per gallon
Diesel Fuel
The BTU value for diesel fuel
is approximately 147,000
BTU per gallon
Diesel Fuel
As with gasoline, diesel fuel is a by-product of the distillation of crude oil. Diesel fuel is a hydrocarbon with different chemical properties
than gasoline. Diesel fuel is part of the “middle distillates” derived from crude oil. This means that diesel fuel is “heavier” than gasoline
but “lighter” than oil used for lubrication (i.e. motor oil). There are numerous advantages to diesel engines, due to the properties of the fuel
used. Some of these advantages include:
• Thermal Efficiency - Diesel fuel produces more power than gasoline. In other words, Diesel fuel has a higher energy content.
One gallon of gasoline contains about 125,000 BTU of heat energy. In comparison, one gallon of diesel fuel contains about 147,000
BTU. This advantage in thermal efficiency, adds up to increased fuel economy.
• Increased Durability - Due to the lubricant properties of diesel fuel, piston ring life is greatly increased. Gasoline has more of a
detergent quality which tends to decrease piston ring life. It is not uncommon for light duty diesel passenger vehicles to have an
engine which lasts more than 200,000 miles.
• Improved Emissions - Diesel fuel contains more carbon atoms per gallon and therefore will emit more CO
increased efficiency of a diesel engine allows for an overall reduction in CO
(with excess air), and produce lower levels of HC, CO and CO
overall. The only area where diesel engines do not excel are in NO
. The lower volatility of diesel fuel, allows for less evaporative emissions
2
and Particulate Matter (PM). But, new technology allows diesel
X
(per mile). In comparison, diesel engines are run leaner
2
per gallon. However, the
2
engines to comply with prevailing emission standards.
Diesel Fuel Types
Diesel #2Diesel #1
The term “diesel fuel” is a generic term, it refers to any fuel for a compression ignition engine. As mentioned before diesel fuel is derived
from the “middle distillates” of crude oil. There are other similar products in this range such as kerosene, jet fuel and home heating oil just
to name a few. However, each of these products is designed for a specific application. In theory, these additional products may work in a
diesel application, but it is not recommended. Diesel fuel has specific properties which are designed to offer the best reliability, the best
fuel economy and the highest compatibility with engine and fuel system components.
As far as passenger cars are concerned, there are two main types of diesel fuel. These are Grade 1 and Grade 2. Usually referred to as
Diesel Fuel #1 and Diesel Fuel #2. Mostly, Grade 2 is used for passenger cars and is the most widely available.
The difference between diesel fuel #1 and #2 is addressed in the following:
• Diesel #1 has about 95% of the BTU content as #2 diesel.
• Diesel #1 has a lower viscosity and provides less lubrication to the fuel system components such as the fuel pump and injectors.
• Diesel #1 has a lower waxing point than #2 and will perform better a low ambient temperatures.
• Diesel #1 usually has a slightly lower Cetane rating than #2, but is above the minimum rating of 40.
Diesel Technology
29
Octane
92
Cetane
51
30
Diesel Technology
Winter Fuel
Petroleum companies generally offer “winter” and “summer” grade
fuels on a seasonal basis. Winter fuel is created by blending a specific amount of #1 Diesel fuel to a quantity of #2 Diesel fuel. This
lowers the freezing (waxing) point to prevent fuel filters from
clogging or the fuel from causing any cold weather starting problems.
In the heavy trucking industry, there have been some other methods to “winterize” diesel fuel. Some of these methods include
adding kerosene or other fuels to improve cold weather starting
not
ability. However, this is
recommended for passenger cars and
may, in fact, cause engine or fuel system damage. Therefore, the
only recommended method is to purchase diesel fuel from a reputable retailer
Cetane Rating
When rating gasoline, the term “octane” has been used to refer to
the anti-knock quality of a fuel. Octane rating refers to the resistance to prematurely ignite under pressure. When the octane number is higher, the fuel is more resistant to pre-ignition and therefore
engine knock. Therefore, a higher octane number is more desirable. For example, today’s octane ratings range from 87 to 93 for
commercially available passenger cars.
In Diesel applications, the term “cetane” is used to rate fuel quality.
However, the desired fuel quality goals are different for diesel.
The cetane rating of diesel fuel refers rather to the “ease of ignition”. After all, a diesel engine is a “compression ignition” engine
and therefore, it is more important for diesel fuel to combust easily
under pressure. Cetane ratings are in a range of 0 to 100. 100 is
an indicator of pure Cetane (n-hexadecane), or the most combustible. Most commercially available diesel fuel has a cetane rating of about 45. A rating of 40 is usually considered to be the
absolute minimum rating for today’s passenger vehicles. Newer
BMW vehicles will require a Cetane rating of 51. Always check the
owner’s manual to see the minimum fuel requirements and the recommended cetane number. A higher cetane rating also contributes to better starting especially in cold weather. When possible, it is always better to use fuel with a higher cetane rating. Also,
a higher cetane number equates to a reduction in NO
and particu-
X
late matter emissions.
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