Application Engineering Bulletin
Application Engineering Bulletin
Application Engineering Bulletin
Engineering
Bulletin
Subject This AEB is for the following applications:
Stationary Natural Gas Engine
Selection and Adjustments as a Automotive Industrial Marine
Function of Fuel Quality
G-Drive Genset
Cummins Confidential
AEB 70.31
Page 2 of 14
• The fuel must be taken from a point such that oil, water, and other contaminates from the distillation
process will not enter the engine.
• There should be no visible traces of oil in the intake system. A separate coalescing filter must be
installed and maintained if any liquids are detected in the fuel.
• When propane is used as a fuel, temperatures below -25° F require heated fuel lines and a heated
propane storage tank.
Introduction
The composition of a fuel affects the knock resistance and energy output of that fuel. Some fuels, such as HD5
Propane, are standardized and can be considered a constant in the design of an engine package during the
application phase. Natural gas composition, on the other hand, will vary with time and location. This is an
important factor in determining the size, type, and compression ratio of an engine for a given application.
Different natural gas compositions have varying effects on engine performance. Dry processed natural gas,
sometimes called “pipeline” natural gas, generally has both good knock resistance characteristics and
acceptable energy output. Other types of natural gas, such as field gas, can have varying compositions. For
example, a fuel can have high knock resistance characteristics but a low energy output. Detonation will not be a
problem in this case but the engine may require a power derate because of the low energy output. On the other
end of the scale, a fuel can have low knock resistance characteristics with a high energy output. The engine will
not require a power derate because of energy output of the fuel, but may require a derate or timing adjustment
because of detonation. This bulletin is intended to help define what actions are required when considering a
Cummins stationary natural gas engine with regard to fuel composition and quality at a specific site.
AEB 70.31
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Table of Contents
Summary of Fuel Quality and Performance Requirements .................................................................................... 1
Introduction.............................................................................................................................................................. 2
Table of Contents .................................................................................................................................................... 3
1. Definitions:.................................................................................................................................................... 4
2. Discussion: ................................................................................................................................................... 5
2.1. Fuel Characteristics ............................................................................................................................... 5
2.2. Types of Fuels ....................................................................................................................................... 5
2.2.1. Dry Natural Gas ................................................................................................................................. 5
2.2.1.1. Sweet Gas ................................................................................................................................ 5
2.2.1.2. Sour Gas ................................................................................................................................... 5
2.2.1.3. Field Gas................................................................................................................................... 5
2.2.1.4. Coal Bed Methane/Low BTU .................................................................................................... 6
2.2.1.5. Digester Gas ............................................................................................................................. 7
2.2.1.6. Landfill Gas ............................................................................................................................... 7
2.2.2. Propane ............................................................................................................................................. 7
2.3. Fuel System Plumbing and Filtration ..................................................................................................... 8
2.3.1. Natural Gas........................................................................................................................................ 8
2.3.2. Propane ............................................................................................................................................. 9
2.3.2.1. Propane Vapor.......................................................................................................................... 9
2.3.2.2. Liquid Propane........................................................................................................................ 10
2.4. Detonation vs. Fuel Quality, Compression Ratios, and Aspiration ...................................................... 11
2.5. Determining Lower Heating Value and Methane Number for Natural Gas ......................................... 12
2.5.1. Calculations and Supporting Documentation .................................................................................. 12
2.5.2. Gas Analysis Tool Available on GCE .............................................................................................. 12
2.6. Gas Analysis Samples ......................................................................................................................... 13
3. References: ................................................................................................................................................ 13
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1. Definitions:
Heating Value
The heating value is a measure of the suitability of a pure gas or a gas mixture for use as a fuel; it indicates the
amount of energy that can be obtained as heat by burning a unit of gas. (ASTM Standard D 3588)
Methane Number
Methane number is defined as a scale to calculate knock potential of natural gas in a spark ignited engine,
relative to the reference fuels. Since methane has an octane number approximately 120 to 140, the octane
scale could not be used and a correlation relating octane number to methane number was developed. The
reference fuels for methane number are methane as the high reference fuel (100) and hydrogen as the low
reference fuel (0).
The following terms are defined in AEB 79.01 and CES 14604 but are repeated here to clarify the discussion in this
bulletin.
Mass Percent
Mass Percent is defined as the molecular weight of each component times the volume percent of that
component divided by the molecular weight of the mixture.
2. Discussion:
2.1. Fuel Characteristics
Commercial dry processed gas (DPG) and field gas fuels that are used in stationary natural gas engines have a
combination of inert gases and combustible hydrocarbon gases. The hydrocarbon fuels are made from carbon
and hydrogen atoms. Fuels that have a greater number of carbon and hydrogen atoms are commonly referred
to as “heavies”, which relate to hotter fuels.
Non-hydrocarbon gases such as nitrogen (N2), hydrogen (H), and carbon dioxide (CO2), tend to dilute the fuel.
Because the gas sample can vary from site to site it is important to closely analyze each site to ensure proper
engine performance and required adjustments.
When water vapor and sulfur oxides are present during combustion, sulfuric acid compounds will form. This
condition will shorten the life of all internal components, specifically the oil cooler, piston rings, cylinder liners,
valve guides and bearings. Sour gas fuels will generally need to be treated to remove all presence of water
vapor. In addition, if the hydrogen sulfide content is above 24 ppm, the sour gas will need to be treated to
remove the hydrogen sulfide. The use of sour gas as a fuel will require high ash oil not more than .85% of
sulfated ash with a high TBN number that meets a CD API specification to help neutralize the acid.
Low BTU Kits may be required to operate properly when LHV is less than 900 BTU/cuft. Use the following chart
below to determine the proper kit and engine adjustments. To determine Low BTU effects, use the Gas
Analysis Tool on the Industrial page of the Global Customer Engineering (GCE) site (www.gce.cummins.com).
AEB 70.31
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2.2.2. Propane
Propane processed to HD-5 specification standards of 95% propane purity with the remaining 5% not heavier
than butane may be used on naturally aspirated engines or turbocharged engines with LCR pistons.
2.3. Fuel System Plumbing and Filtration
Many countries and cities have very specific gas plumbing requirements; be certain to consult local gas codes
and regulations for natural gas and propane plumbing requirements.
Typical stationary natural gas engines will have gas pressure regulators and fuel shut off valves that are engine
mounted. The engine requires 5 +/- 2 “WC at the carburetor and 15 +/- 5 “WC to the engine mounted regulator.
The gas pressure to the carburetor is adjusted at the engine mounted regulator.
Engines that don’t have an engine mounted regulator will still require 5 +/- 2 “WC pressure to the carburetor.
The primary high pressure regulator is used to adjust fuel pressure to the engine mounted regulator.
There can be no oil carry over from the gas compressor or fuel source. The fuel supply must be free from oil,
dirt, and debris. Care must be given on newly commissioned engines to ensure that dirt, rocks, pipe sealer and
Teflon tape is not ingested into the engine.
Cummins Confidential
AEB 70.31
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2.3.2. Propane
Cummins stationary natural gas engines use two different types of propane fuel systems: Propane Vapor and
Liquid Propane. Since the composition of HD-5 propane is standardized, compression ratio and fuel derate are
independent of the destination site; the factory predetermines compression ratio and fuel derate for engines sold
with propane fuel systems. Not all propane is sold to the HD5 standard; get a fuel sample if any doubts exist
about the composition of the fuel.
Note: Propane will not vaporize at temperatures -40° F and below. For Cummins stationary natural gas
engines, temperatures below -25° F require heated fuel lines and a heated propane storage tank.
On propane vapor systems, engine vacuum draws propane in from the storage tank through the vaporizer, the
fuel shutoff, the regulator, and then the carburetor. The carburetor maintains the air/fuel ratio. Although it is
possible to extract the propane vapor from the top of the tank, an external vaporizer is strongly recommended to
convert liquid propane to a vapor.
On liquid propane fuel systems, liquid propane is supplied to the engine at the filter and shutoff valve assembly,
through the evaporator, and then to the carburetor. The carburetor maintains the air/fuel ratio.
Detonation is ignition of the mixture by pressure energy (supersonic shockwave) rather than the ignition energy
being supplied by the spark.
Detonation caused by fuel composition can be controlled prior to engine selection for a particular site through
proper application of compression ratios, aspiration, and power deration. To determine the proper compression
ratio and aspiration for the site, use the site gas analysis report to calculate the Methane Number and the LHV
of the fuel.
Gas Analysis with a methane number of 80 and higher can use turbocharged engines with HCR pistons.
Methane numbers greater than 45* and less than 80 will require LCR pistons or a naturally aspirated engine.
Turbocharged engines with HCR pistons are designed to operate on higher methane fuel such as dry processed
natural gas, which has a methane number of 80 to 100. HCR pistons produce higher temperatures and
pressures leading to increased potential for knock. Cummins stationary natural gas engines should not be
operated with methane numbers lower than 45*. * See the Base Engine Datasheet for actual low MN limits.
Because the methane number is based on the level of “Heavier” hydrocarbons in the sample, the hotter the fuel
the lower the methane number will be. This simply means the fuel is “Knock” sensitive. It is possible to have a
high methane number and a very low LHV. In this case the engine may require power deration to accommodate
the low energy output of the fuel. Caution must be observed when the LHV is between 750 and 900 BTU/ft3,
although the methane number may be high the engine may have trouble pulling power due to the low BTU fuel.
The engine must be derated 1% for every 25 BTU/ft3 below 900 down to 750. For fuels with LHV below 750,
consult the factory for derate.
Sometimes timing adjustments may be required to compensate for changes in ambient temperatures or fuel
quality.
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2.5. Determining Lower Heating Value and Methane Number for Natural Gas
As discussed earlier, the two key elements of natural gas composition that effect engine performance are the
lower heating value (LHV) and the methane number. These properties can be determined either through
calculations found in the standards and bulletins given throughout this document or by using the Gas Analysis
Tool. A gas analysis for the proposed site is required for either of these methods.
The Gas Analysis Tool calculates the LHV and methane number of a fuel for a specific site. The tool will help
determine the compression ratio, power derate, and ignition timing associated with the fuel and can flag
conditions that indicate that a fuel is not acceptable for use in a Cummins stationary natural gas engine. The
Gas Analysis Tool can also help determine power derate and timing specifications related to site conditions
such as ambient temperature and altitude.
Refer to the Instructions page of The Gas Analysis Tool on GCE for specific step by step instructions and information on
updates and changes to the tool.
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Sample 1: Typical pipeline quality natural gas, methane number greater than 80, HCR pistons are acceptable
and no derate required.
Sample 2: Methane number is greater than 80, HCR pistons are acceptable. The LHV is less than 900 BTU/ft3,
so a derate of 1% per 25 BTU/ft3 below 900, or 5.36% derate for low BTU fuel.
Sample 3: Methane number is less than 80, HCR pistons are not acceptable. Methane number is also below
45 as well, a naturally aspirated engine or LCR pistons are not acceptable either. The fuel should not be
considered acceptable. If the methane number was 45 or greater the fuel would be acceptable for a naturally
aspirated engine or turbocharged engine with LCR pistons, though consideration must be given to timing,
oxygen, and turbine inlet temperature in this case.
3. References:
AEB 79.01 “Natural Gas Fuel Performance Specifications”
ASTM D 3588, Calculating Heat Value, Compressibility Factor, and Relative Density (Specific Gravity) of
Gaseous Fuels
John Kubesh, Steven R. King, William E. Liss, “Effect of Gas Composition on Octane Number of Natural Gas
Fuels,” SAE Paper 922359
Revision History:
Date Author Description Page(s)
May 18, C.McFarden Added QSL9G Low BTU Table. Revised spring color to Red 6
2010
Jan. 2010 C.McFarden Added G8.3 all model,G8.3E,GTA855 256, GTA8.3 175 to Low BTU 6,11
Table. Revised minimum MN numbers for HCR from 70 MN to 80MN
July 2009 C.McFarden Replaced Instructions for Gas Analysis Tool with a reference to the 12-15
instructions available with the tool on GCE
Mar 2009 C.McFarden Added KTA19GCE Low BTU data 6
Mar 2008 B. Revier Added KTA19GCSLB data, part numbers for kits, and updated branding 6, 11-14
Jan, 2008 C.McFarden Revised Info to Low BTU table for fuel less than 900 BTU/cuft 6
Aug, 2007 C.McFarden Add GTA8.3SLB Info to Low BTU table for fuel less than 900 BTU/cuft 6
Aug, 2007 C.McFarden Edit methane requirement and add derate performance requirement 1
Aug, 2007 C.McFarden Edit causes of detonation bulleted list 10
Jun, 2007 C.McFarden Add Low BTU table for fuel less than 900 BTU/cuft and Title Change 1,2,6,10
Feb, 2006 C McFarden Removed “Consult your local distributor application engineer.” From 6
Section 2.2.1.4. Coal Bed Methane Gas
Jan, 2006 C McFarden Inserted Section 2.2.1.4. Coal Bed Methane Gas; Revised Headings 6
under 2.2 Types Of Fuels to accommodate new section
Oct, 2004 C McFarden Original Release (future changes will be in blue text) All