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Check out The Fuel Pulse Show Podcast

Check out The Fuel Pulse Show Podcast

Check out The Fuel Pulse Show Podcast

Check out The Fuel Pulse Show Podcast

Check out The Fuel Pulse Show Podcast

Check out The Fuel Pulse Show Podcast

Check out The Fuel Pulse Show Podcast

Check out The Fuel Pulse Show Podcast

Check out The Fuel Pulse Show Podcast
Check out The Fuel Pulse Show Podcast

Overview Of LPG Problems

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LPG in the United States is used mostly in home/industrial heating and cooking systems and large municipal transportation fleets.  In both applications, LPG offers cleaner combustion at an inexpensive fuel cost.  Although it is a much cleaner burning fuel than diesel or gasoline, contrary to long-held belief, LPG is not entirely without its fuel-related performance issues.

Overview

LPG (Liquefied Petroleum Gas), CNG (Compressed Natural Gas), and natural gas are gaseous fuels containing common components like propane and butane. In the US, LPG and propane are often used interchangeably, typically referring to a blend of 70% propane and 30% butane, with trace additives for leak detection. The blend ratios may vary slightly across states, like California having distinct specifications.

During crude oil refining, LPG is the first byproduct in the distillation process, produced alongside gasoline and diesel. While gaseous at normal temperatures, LPG is usually compressed and cooled for storage, with compressed LPG having 270 times the energy value of its gaseous form.

LPG usage is more prevalent in Europe and Asia due to environmental concerns and a well-established distribution network. In the US, LPG is primarily used for home heating, industrial applications, municipal transportation fleets, and consumer products like gas grills. LPG-fueled personal transportation is more common in Europe and Asia.

For the US to match the LPG usage levels seen abroad, significant improvements in distribution infrastructure are needed. Developing nations like China and India heavily rely on LPG for transportation, driven by environmental commitments. China, for instance, at one time was aiming for a 25% reduction in pollution emissions over a five year period - and were relying heavily on LPG to do that. 

Good Points About LPG Fuels

LPG molecules are small – 3 and 4-carbon chains compared to the 8-18+ carbon-chain molecules found in gasoline and diesel – and burn very cleanly compared to gasoline and diesel.  This better combustion means less carbon buildup in the engine and longer life for both spark plugs and lubricating oil.  This is a plus for all kinds of consumers who need to have maximum fuel value from their vehicles, large and small.

Fuel-combustion emissions are also pretty low for LPG compared to the popular automotive fuels – unburned hydrocarbon and particulate emissions are very very low, as are sulfur gas emissions and NOx (nitrogen oxide) emissions, which are both precursors for smog in polluted urban areas.  Evaporative emissions (such as what happens when fuel is dispenses – some of the fuel escapes into the air) are very low due to the necessary closed LPG fuel delivery systems at dispensing stations.

LPG has a lower gross sulfur content than gasoline, reducing the potential for corrosion in storage systems.

These facts make LPG a favorite fuel for environmentally-conscious consumers, including local governments who face mandates from their constituency and higher up in the governmental ladder to be more “green”. All of this adds up to the fact that  LPG fuels are great for the environment, apart from the carbon emissions they generate in the form of CO2.

LPG Fuel Issues

Because LPG is so clean burning most consumers and even some gas fuel distribution professionals are unaware that LPG fuels aren’t without their problems or room for improvement.

Vehicle Fuel Availability in the United States

Very few LPG-only consumer vehicles are sold in the USA each year.  You can purchase conversion kits that will turn your regular gasoline-powered vehicle into a dual flex-fuel vehicle that can switch between gasoline and LPG.  Conversion kits cost $2000-$4000.  Unfortunately, even if you choose to do this, the simple availability of vehicle LPG fueling stations is a prohibitive problem in the US for further expansion of this kind of green fuel. California has the most vehicle “propane” filling stations – about 600 of them. Across the nation, only 3% of the LPG used is sold for vehicle use.

Mileage Range for Vehicles

Consumers in the United States who do have flex-fuel LPG vehicles can face mileage range issues with their LPG tanks.  Remember that compressed LPG has a different density than gasoline or diesel. A typical LPG car like the converted 2008 Honda Civic can get as much as 36 mpg.  That’s great mileage.  Unfortunately, because of the nature of LPG compression, despite the 36 mpg (24 mpg city), the Civic can only go about 185 miles on a full tank of LPG fuel.

Deposit Buildup from Refinery-Sourced Impurities

LPG (Liquefied Petroleum Gas) sourced directly from the ground comprises a clean mix of propane, butane, and other hydrocarbons, free from double-bonded olefin impurities like propene. This pure LPG combusts cleanly, generating substantial heat energy (21,000 BTUs per pound) with minimal deposits and harmful emissions like carbon monoxide.

However, some market-available LPG is produced via refinery cracking methods aimed at maximizing gasoline and diesel outputs, resulting in LPG with unstable alkenes and olefins. Cracking breaks down longer molecules into shorter ones, producing additional LPG, albeit impure due to cracked molecules.

Cracked LPG fuels contain reactive alkenes, prone to interactions with each other, water, and other environmental molecules (S, O, N), forming longer-chain polymers leading to heavy-end deposits. These unstable molecules, due to their double-bonds, react easily, creating long polymer molecules that, given their length, do not dissolve well in LPG as propane is a poor solvent for such substances. Consequently, they precipitate out before and during vaporization, becoming unrecoverable.

These deposits accumulate in vaporizers, converters, vaporizer lines, fuel injectors, injector metering orifices, and burners, whether in vehicles or home heating systems powered by propane. Due to their heavy nature, these deposits linger and build up where they first settle, posing challenges to the equipment's efficiency and potentially leading to maintenance issues over time. This underscores the importance of sourcing pure LPG to avoid the complications associated with cracked LPG fuels.

The Effect of LPG Deposits on Performance

Deposit buildup in fuel systems, stemming from impure LPG, adversely impacts fuel flow and air/fuel mixing, diminishing system efficiency and escalating emissions. This buildup progressively hampers fuel efficiency in heating or automotive systems. Deposits not only hinder efficient fuel combustion but can absorb LPG, releasing it slowly over time, disrupting the system's designed operation.

In vehicles utilizing LPG, deposit accumulation from olefins elevates the engine's octane requirement. Deposits in combustion chambers and cylinders alter the volume within, impacting the octane level needed for precise fuel ignition. LPG boasts a high octane rating of 96-100, making the deposit effect more pronounced compared to gasoline engines optimized for 87 or 89 octane gasoline.

Cold weather startups become challenging with deposit accumulation, as they impede fuel vaporization and flow through the delivery system, particularly problematic for LPG systems expected to initiate instantly in winter. Deposits, especially in fuel vaporizers, deter proper fuel vaporization, affecting performance in cold conditions. This issue becomes a big problem if the vaporizer gets fouled with deposits, hindering the fuel from vaporizing adequately in order to function optimally. Through these scenarios, the adverse implications of deposit buildup in systems utilizing LPG, especially impure variants, are highlighted, emphasizing the importance of preventive measures and fuel purity.

Equipment Wear

When used in vehicular applications (cars and trucks), LPG proves to be a dry fuel that doesn’t provide the same kind of lubrication for critical fuel delivery parts that liquid fuels can.  Over time, LPG drivers tend to find excessive wear on certain critical engine parts.  Valves, injectors and compression rings can be the most common parts affected.

In furnace systems, some built-up deposits can be abrasive and may break off in the turbulent air flow of the fuel delivery system.  When this happens, they can wear on metal surfaces and cause damage.  This typically happens slowly over a long period of time, but can end up leaving you with costly repair bills for system maintenance.

To prevent excessive wear on vehicular and industrial or home furnace system parts, it can be beneficial to treat the LPG fuel with a lubricant.

Water and Moisture Collection

Contrary to perception, water and moisture can get into the LPG fuel via the supply chain.  When this happens, fuel fouling can result as the fuel undergoes oxidation while reaction with the oxygen in the water.  Oxidation reactions cause the pure propane/butane molecules to react and polymerize (stick together), forming heavy deposits that can sink to the bottom of the tank or be carried with the LPG fuel into downstream storage containers where they end up accumulating and causing deposits in the vehicles and furnace systems that ultimately burn the fuel.

Conclusion

LPG and other compressed gases are excellent choices for consumers looking for a clean fuel that is relatively friendly for the environment, burning with low emissions and soot output. Vehicles running on LPG fuel (if you can find them) have low emissions and get high miles per gallon (although the volume of LPG which can be stored in a vehicle is less than a gasoline or diesel fuel tank capacity).  LPG’s problems are pretty minor compared to biodiesel or ethanol and can be resolved pretty easily if the fuel supplier additizes the LPG fuel.

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