NGVConnection Newsletter - December 2017

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How to Minimize Costly ($42,000?) Oil Carryover Problems in Heavy-Duty Natural Gas Engines

By Annalloyd Thomason, Vice President/General Manager, NGVi

They are the most common performance complaints for heavy-duty natural gas vehicles:

  • Hard to start
  • Idles rough
  • Hesitates under acceleration
  • Low power
  • Sometimes stalls 

The most common culprit? Oil contamination in the fuel. 

Oil contamination in heavy-duty NGVs can be hard to diagnose and even harder to remedy—especially if the vehicle technician is unfamiliar with compressed natural gas and natural gas engines.  If the quantity of oil is significant enough to pass through coalescing filters onboard vehicles, it contaminates the pressure regulator and engine sensors, clogs filters, causes premature spark plug failures, and even causes pistons or rings to fail…the list goes on. 

None of these components is inexpensive to replace, and if the technician doesn’t know what to look for or how to identify oil as the problem, thousands of dollars in parts can be replaced while the real problem remains unsolved: oil contamination in the fuel. NGVi recently worked with one small refuse fleet of 11 vehicles that has purchased just over $42,000 in coils, plugs and sensors in 15 months…all because of oil contamination in the fuel.

So why oil?  At CNG fueling stations, compressors increase the pressure of natural gas to 3,600 psi or higher to allow adequate quantities of natural gas to be stored onboard vehicles.  Compressors are extremely reliable pieces of equipment that require lubrication to operate properly. CNG fueling stations are designed with filtration systems to protect against oil “carried over” from the compressor into the fuel dispensed into vehicles, but for a variety of station maintenance reasons, many CNG stations still dispense oil. 

If not properly filtered throughout the compression and dispensing process, vaporized oil becomes entrained in the natural gas in its high-temperature and high-pressure state, but drops back out as a liquid when the temperature, and in some cases pressure, are reduced. That liquid or aerosol oil flows into the engine and contaminates every component it touches.


Contaminated components will not function properly, and either the engine’s performance will suffer, or at the extreme, pistons will be damaged and the engine will fail. 

So what’s a heavy-duty fleet manager to do?  There are a few musts.

  • To help reduce the amount of oil getting into vehicles, be sure to train drivers and/or fuelers to watch for oil in the fueling nozzle and receptacle. The best way to prevent oil problems in the vehicle is to never let it get there in the first place.

  • Train technicians on the unique components of heavy-duty natural gas fuel systems and engines, how they function and how to diagnose them. This will allow your technicians to distinguish between a fuel problem, a fuel system problem or an engine problem. Nearly every week, NGVi works with clients who, prior to training, believed every problem they were experiencing was an engine problem when, in fact, many problems were associated with oil contamination.

  • Excess oil in low pressure coalescing filters is the most significant early indicator of oil in the fuel stream.  Heavy-duty fleets should include draining low-pressure coalescing filters as part of the daily driver pre- and post-trip inspections required by the Federal Motor Carrier Vehicle Safety Administration. Drivers should record the amount of liquid from the low-pressure filter daily on the DVIR, and if the amount exceeds about a tablespoon of liquid, report the condition to fleet maintenance and have it checked out. Early detection of oil in the low-pressure filter is the best way to ensure that the beginning of an oil carryover problem does not totally contaminate sensors and other engine components.   

  • Implement policies and training for drivers that require them to monitor for basic visible fuel system component integrity—especially dust covers on the fuel receptacles. Dust covers are not just nice little devices to make the receptacle look better—they are there to prevent dirt and other debris that might collect on the receptacle from being forced into the fuel system during the fueling process—creating or further complicating a fuel quality problem. 

  • If you own and operate the CNG station that fuels your vehicles, make sure maintenance practices are being followed precisely. Weekly draining of coalescing filters and ASME storage vessels at the station is essential and will alert station maintenance technicians to a potential problem. Coalescing filters are designed to remove liquid and aerosol oil and water from the CNG fuel stream.  If you can see oil collected in the dispenser filter housings, either there is not enough filtration designed into the station or the filters are not being drained frequently enough. A pressure-drop indicator installed across one or more coalescing filters in series closest to the dispensers is the BEST way fueling station maintenance technicians can determine when it’s time to change filter elements.

  • If your vehicles fuel at public sites, make sure the fuel provider guarantees fuel quality according to a specification that includes maximum water and oil content, among other variables. If the fuel provider can’t or won’t provide that fuel specification, find another fuel provider if at all possible.

Implementing these simple measures can help heavy-duty fleets save a lot of money and headache. Although they require effort on the front end, they are surely worth it because once oil is in the vehicles, it is extremely difficult (if not impossible) to eliminate, and can cause problems over the entire vehicle life. 

If you’re experiencing a heavy-duty CNG engine performance problem or you suspect oil carryover in your fuel and would like technical assistance, contact us at 800-510-6484 or

New Technology From Parker Tube Fittings Takes ORFS Fittings to the Xtreme
By Ted Amling, Sr. Project Engineer, Parker Hannifin Corporation, Tube Fittings Division

Effectively sealing fluids and gases at extreme temperatures is always a challenge, due either to the temperatures, chemical compatibility, limited connection options or space. Finding reliable connections for extreme cold, such as LNG systems, or extreme heat, such as fuel gas lines on combustion turbines, can be a challenge for engineers who often are not familiar with the options available for tube and pipe interconnect systems.

Sealing methods typically fall into two types for extreme temperatures. The first type is direct metal-to-metal sealing with no replaceable sealing element. This type includes compression fittings and 37° flare fittings. The second type uses replaceable gaskets to make the seal including ANSI flanges and its many variants, as well as the multitude of metal seal shapes to replace O-rings, such as c-seals.

There are limitations, however, to these two methods. Direct metal-to-metal sealing can be difficult to work with due to low tolerance for small scratches and imperfections. This sealing has limited reuse due to the required deformation of the sealing surfaces, and assembly procedures can be confusing to new users. Replaceable gasket sealing is an improvement over metal to metal sealing. However, traditional systems such as ANSI flanges require large space claims, while O-ring replacement metal seals can be cost prohibitive and typically have limited reuse potential.

In response to these limitations, Parker’s Tube Fittings Division has developed a sealing system that extends the use of industry standard O-ring Face Seal Fittings (ORFS) to operate at extreme temperatures.  Two new patented seals have been developed to work on both the ORFS tube end, as well as SAE J1926 stud ends. Parker’s Seal-Lok Xtreme™ is an SAE J1453 compliant ORFS fitting that uses patented metal sealing technology to provide -328°F to 1200°F sealing capability.

Operating temperatures for traditional ORFS fittings are limited by the seal material. Seal materials such as perfluoroelastomers (FFKM) can operate up to 600°F max, while very few elastomer seals can achieve more than -70°F. These materials can be very cost prohibitive and still do not extend the temperature range much past what more common FKM or HNBR seals can achieve.  Metal sealing technology is really the only option for extreme temperatures, and the Seal-Lok Xtreme™ seals easily operate from -328°F to 1200°F, while providing a much broader chemical compatibility as a bonus. These seals are made from316 stainless steel and are coated with silver to promote sealing and prevent galling at high temperatures. Combined with 316SS fittings and tubes, this system provides a thermally stable connection with instrumentation-grade sealing available on industry standard ORFS fittings.

The Seal-Lok Xtreme™ system has been rigorously tested for both sealing performance as well as system robustness. Therefore, the Seal-Lok Xtreme™ system, when combined with Parker’s Parflange™ weldless flanging technology, brings all of the advantages of the ORFS fitting to markets and users previously unfamiliar with their many benefits.. This has made it one of the most popular fittings for high-pressure hydraulics on the market.   

Some of the product benefits include:

  • assembly to torque
  • no damage from overtightening
  • zero clearance for easier plumbing
  • excellent vibration resistance
  • unlimited reuses
  • reduced assembly/ disassembly times
  • positive seal retention
  • enhanced anti-galling dry film lubricated nuts
  • replaceable silver plated seals
  • available in tube and hose sizes 1/4" to 2" (6 mm to 50 mm)
  • AISI/SAE 316/316L stainless steel material (fittings and seals)
  • working pressures up to 6000 psi
  • meets requirements of ASME B31.1 and B31.3

Next time you are considering what product to use to connect your extreme temperature fluid or gas system, or if you are unhappy with the current choices on the market, consider Parker’s new patented Seal-Lok Xtreme™ ORFS fitting as an option.

Reduce Fleet Downtime: Understanding CNG Ignition Systems
By Kasia McBride, Marketing Manager, NGVi

Natural gas engines differ significantly from their diesel counterparts, and technicians who maintain them must have a full understanding of their operation and specific diagnostic parameters.  Perhaps the most prominent difference these technicians must deal with is the fact that natural gas fuel ignites via spark ignition--not compression ignition, as in diesel engines. Natural gas vehicle engines use an ignition system, including spark plugs and coils, to ignite their fuel/oxygen mixture.

Obviously, the ignition system is a critical part of engine operation. Even small ignition problems can significantly impact engine performance. To avoid these problems, and unnecessary maintenance costs, technicians should always make sure all parts of the ignition system are properly installed, calibrated, and maintained. This article will discuss the factors affecting different parts of the ignition system such as plugs and coils, additional maintenance concerns and specific strategies to maximize component life.


Why Ignition Systems in Natural Gas Engines Can Be “Tricky”

There are two major engineering obstacles associated with spark plugs used in natural gas powered engines. First, natural gas has a much higher ignition temperature compared to traditional liquid fuels. Second, the spark plugs are under much higher cylinder pressures due to the related higher compression ratios. Both situations put a lot of stress on secondary ignition components.

Because natural gas is harder to ignite, the gap between the electrodes of the spark plug must be properly sized in order to help the spark jump the gap. If the gap is incorrect it will affect the energy needed to spark, which can cause misfires or poor ignition of the fuel mixture. For instance, if the gap is too wide, the spark is going to take the path of least resistance and go to the ground through another source, causing misfire. This could potentially damage coils and coil extensions.

Proper Gap is Important

To avoid this situation, engine and ignition manufacturers publish recommended gap measurements for the spark plugs. The recommendation for the gap in the spark plugs used in Cummins engines is .013 to .015 in. The recommended gap varies widely for light-duty engines due to variables, although  most gasoline engines start out with the plugs set anywhere from .035 to.045 in. or higher. For light-duty natural gas vehicles, technicians should check with the fuel system manufacturer or  upfitter for the recommended spark plug gap. 

It is important to always check the gaps of the plugs when installing new ones. If the gaps are not all the same, combustion in the cylinders will be uneven or incomplete, which over time will cause undue wear on various components. Cummins recommends to visually inspect plugs to ensure that the ground electrode is parallel to the center electrode and aligned along the center line of the plug.

Because of the thin, protective coating (typically made of iridium) on the spark plugs, it is not recommended that the gap of the plug be changed. Cummins recommends to only use a wire spark plug gap tool to check the specifications. Careful visual inspection should be made as to whether the right spark plugs are used and that they have no signs of: flash-over onto the porcelain, electrode deposits, worn or missing electrodes, excessive or insufficient gap, or any signs of aluminum or other contamination.

Coils Can Be Tricky Too

In addition to the size of the gap, the voltage required to bridge it is affected by the cylinder pressure (the spark needs a lot of force to jump the gap) and the air/fuel mixture, which is not very conductive so there is a lot of resistance. This voltage is produced by the ignition coil, which produces the spark needed to create a sufficiently high temperature so that the fuel surrounding the spark will actually ignite. The coils on a Cummins engine will create a spark that is approximately 30,000°F.

Due to the high temperatures that can be present in the spark plug well, strain can be placed on the materials that help insulate the electromagnetic field at the coil. The potential for cracking becomes greater under conditions in which the temperature fluctuates dramatically from cold to hot. If a crack does exist in the insulating materials, the electric current will take the path of least resistance through the block, thus bypassing the spark plug completely.

Inspecting the Ignition System Helps Prevent Performance Problems

To avoid major problems with the ignition system components, it is critical, at minimum, to perform the inspection, maintenance and replacement of plugs and coils at recommended manufacturer intervals. If the engine is converted and the plug gaps aren’t changed, there should be recommendations from the vehicle upfitter regarding their correct replacement schedule. The upfitter should also provide documentation specifying the plug gaps for when plugs are replaced.

Early Replacement of Coils and Plugs

Many companies have learned that replacing spark plugs before they can fail can substantially save on the cost of replacing the coils, extensions and/or wires as well. So, in addition to the recommended intervals, preventative diagnostics and maintenance is highly advised. For instance, if the coils and plugs start to fail at 40,000 miles, it can be beneficial to change the plugs at 35,000 to 37,000 miles.

Once Again, Training is the Key

Here is the bottom line: with any new technology, sufficient technician training is a must. Traditional diesel technicians are not commonly familiar with NGV ignition systems, and even seasoned technicians should not be expected to possess the specific knowledge necessary to avoid serious economic impacts from poorly adjusted, poorly calibrated, or damaged components. By better understanding ignition system fundamentals, being able to determine the root cause of ignition problems, and being familiar with the best practices for ignition operation and maintenance, technicians can not only increase the service life of NGV engines, but also save their company thousands of dollars by reducing maintenance costs and vehicle downtime.

CNG Fuel Price Report
From Clean Cities Alternative Fuel Price Report published by National Renewable Energy Laboratory (NREL) for DOE's Clean Cities Program

Overall Average Fuel Prices (as of October 2017)


Nationwide Average Price for Fuel This Report

Nationwide Average Price for Fuel Last Report

Change in Price This Report vs. Last Report

Units of Measurement

Gasoline (Regular)




per gallon





per gallon





per GGE

NGVs and CNG in the News


NGVAmerica Releases CNG Fuel System Inspection Guidance
-- Transport Topics

Flint MTA Partners with Utility on New CNG Station -- NGT News

Oxford County adds CNG plows

Cummins Westport Receives 2018 Emissions Certifications for L9N and B6.7N Natural Gas Engines
-- Oil & Gas 360

Upcoming Training and Certification from NGVi

NGV Essentials and Safety Practices CNG Fuel System Inspector Training
January 30, 2018 Scottsdale, AZ
February 13, 2018 Dallas, TX
March 26, 2018 Bakersfield, CA

With a focus on safety, this one-day course teaches technicians the fundamentals of natural gas, CNG and LNG fuel systems and maintenance practices for NGVs.

January 31 - February 1, 2018 Scottsdale, AZ
February 14-15, 2018 Dallas, TX
March 27-28, 2018 Bakersfield, CA

Two-day session that provides you with the proper techniques for inspecting CNG fuel systems, including on-board compressed natural gas fuel storage cylinders.

NGVi CNG Fuel System Inspector Certification Exam

February 2, 2018 Scottsdale, AZ
February 16, 2018 Dallas, TX
March 29, 2018 Bakersfield, CA

NGVi's CNG Fuel System Inspector Certification Exam delivers a rigorous, independent assessment of the knowledge, competency, and application of skills necessary for technicians to properly conduct CNG fuel system inspections, according to all applicable codes, standards, and industry best practices.

Register Now


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About NGVi

Natural Gas Vehicle Institute is North America’s leading provider of training and consulting on natural gas as a transportation fuel.

Our services address the full range of natural gas vehicle and fueling issues, including:

Technical consulting services – Sizing and designing compressed natural gas fueling stations, vehicle assessments and technical assistance for fleets, CNG fueling station troubleshooting, natural gas vehicle maintenance facilities upgrades, liquefied natural gas fleet and fueling management.

Technical training – NGV Essentials and Safety Practices, CNG Fuel System Inspector Training, Heavy-Duty NGV Maintenance and Diagnostics Training, Light-Duty NGV Maintenance and Diagnostics Training, CNG Fuel System Design and Installation Training, Essentials of CNG Station Operation and Maintenance Training, Essentials of CNG Station Planning, Design and Construction Training and CNG/LNG Codes and Standards Training for Fire Marshals and Code Officials.


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