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Primary Reference Fuels (PRF) for Octane Number Determinations

Tue, May 29th 2012, 13:35 by Indresh Mathur

Primary Reference Fuels (PRF) for Octane Number Determinations

Dr. Indresh Mathur

PRFs are required to determine the combustion quality of gasoline and diesel fuels. The key combustion parameter for gasoline is measured by determination of the octane number of the fuel in a Cooperative Fuel Research (CFR) engine.

Octane Number Fuels

Pure isooctane (2, 2, 4-trimethylpentane) has been assigned an octane number of 100 because of its excellent antiknock properties and n-heptane is assigned an octane number of zero because of its propensity to pre-ignite easily. Therefore, an 80:20 mixture of isooctane and n-heptane has an octane number of 80. In certain circumstances pure toluene is also used as a PRF because it has an octane number >100. ASTM test method D2700 and D2699 describe the methods; Motor Octane Number (MON) and Research Octane Number (RON), respectively. In these test methods, a candidate fuel is combusted in Waukesha CFR engines and its knock characteristics are compared with a fuel composed of PRF grade isooctane and n-heptane. The isooctane specified by ASTM for use in D2700 and D2699 must have a minimum content of 99.75% of 2,2,4-trimethylpentane  and the n-heptane must be minimum 99.75% pure. ASTM requires that PRF toluene specified for use in D2700 and D2699 must have a minimum purity of 99.5%.

In the past, Haltermann supplied Primary Reference Fuels to the North American market but exited the market after being acquired by Monument Chemicals. Effective immediately, Haltermann Solutions is now pleased to again offer PRF fuels to its customers. Haltermann is introducing PRF fuels in stages starting with isooctane and toluene. During our introduction, we wanted to ensure that ASTM members were confident that Haltermann PRF fuels met all the ASTM requirements. To assure compliance to ASTM specification requirements, Haltermann contracted numerous third part labs to analyze our octane PRF fuels for purity. Samples were sent out to the certified contract analytical laboratories listed in Table 1. To-date, test results have confirmed that Haltermann’s PRF grade isooctane and toluene comply with the exacting purity and performance requirements of ASTM and can be used with confidence. The numerical average of the test results and standard deviations are given in Table 2 and Table 3 for isooctane and toluene. These ASTM compliant PRF fuels are now available from Haltermann in 55 gallon drums and 5 gallon pails. The PRF grade toluene is stabilized to prevent excessive peroxide formation.

PRF grade n-heptane and PRF grade 80 octane fuels will be the next additions to our PRF family of products. We expect these high purity products to be available during the 3rd quarter of 2012 after the certification data has been filed with the ASTM.

For more information on Haltermann PRF fuels, please contact Josh Petersen, Haltermann Manager of National Accounts at 615-812-7063  (





































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Differences Between Corn and Sugar Cane Derived Ethanol for Fuels

Wed, Mar 2nd 2011, 09:20 by Indresh Mathur

Differences Between Corn and Sugar Cane Derived Ethanol for Fuels

Corn and sugar cane are the two primary source of feedstock from which ethanol is derived for use in automobile fuels. Our customers have frequently asked, “Are there differences in the corn ethanol sold in the USA and the sugar cane ethanol sold in Brazil?” The answer is not so clear-cut. Our analysis would suggest that further studies are warranted.

In an attempt to provide an answer the above question, Haltermann Solutions procured anhydrous ethanol from two major US ethanol producers of corn ethanol along with hydrous and anhydrous ethanol produced in Brazil from sugar cane, and compared them.

The impurities in ethanol can adversely impact the properties and performance of Ethanol Fuel as an automotive spark-ignition engine fuel. The quantities of impurities like water, acidity, pHe, chloride, sulfate, sodium, potassium, phosphorus, copper, sulfur, silicon, calcium, magnesium etc. in Fuel-Grade Ethanol is controlled within specified limits. The following summarizes the reasons for limiting various impurities:

Water reduces the energy content of the fuel and therefore adversely affects fuel economy and power. Also, water can cause phase separation problems in some ethanol-gasoline blends. Water is soluble in ethanol but ethanol is soluble in gasoline. When there is excess water in a fuel that is comprised of a preponderance of gasoline (i.e. E5-E25), there is phase separation. Water, in anhydrous ethanol, is generally limited to 0.3%, whereas water content of hydrous ethanol is typically in the range of 5-6%.

Acidity and pHe. Aqueous organic acids in very small presence, such as acetic acid, can be highly corrosive to a wide range of metals and alloys. When the pHe of the fuel is below 6.5, excessive corrosion can occur which may result in fuel injector failure and cylinder wear. Acidity (as acetic acid) is limited to 0.007 %m/m.

Inorganic (ionic) chloride compounds can be corrosive and can damage fuel system components.    Inorganic chloride compounds are generally limited to a concentration of

Sulfate levels are generally limited to <4mg/kg.

Phosphorus, like lead, deactivates exhaust catalysts if present in more than trace quantities.

Copper is a very active catalyst and can promote gum formation in gasoline. Copper is usually limited to <0.100mg/kg.

Sulfur is limited in order to protect against engine wear, deterioration of engine oil, corrosion of exhaust systems, and to prevent catalytic muffler deactivation. Sulfur levels are usually limited to <10mg/kg. Generally, sulfur in non-denatured ethanol is lower than sulfur in denatured ethanol because of the sulfur impurity in the natural gasoline typically used to denature the ethanol.

Silicon in ethanol is unacceptable.  Combustion of a fuel that contains silicon results in the formation of silica deposits on the oxygen sensor in the engine exhaust.

Methanol content in ethanol is limited to 0.5 % m/m. This is important to in order to protect against engine and fuel system wear, corrosion, and deterioration.

C3-C5 saturated alcohols usually enter fuel ethanol as by-products of the manufacturing process, and are limited by the producer as a way to control the purity of the ethanol.

The results of the detailed analytical work carried out on the various types of ethanol are given in the attached table. At first glance, there appears to be little difference between corn and sugar cane ethanol. The ethanol content is consistent with whether the particular ethanol being analyzed was anhydrous non-denatured, anhydrous denatured, or hydrous non-denatured.  The heat of combustion is consistent with the water content of the ethanol.

A closer look at the analytical data shows that hydrous Brazilian ethanol derived from sugar cane consistently has higher levels of inorganic impurities as evidenced by the higher levels of sulfate, sodium, potassium, calcium, magnesium and sulfur. While natural gasoline as a denaturant in ethanol generally contributes to higher sulfur levels, it is worth noting that the sulfur level found in the hydrous Brazilian ethanol was higher than the sulfur level found in the natural gasoline-denatured ethanol. It appears sodium sulfate is the major impurity in the hydrous Brazilian cane ethanol. It is reasonable to assume that higher inorganic impurities in the hydrous Brazilian cane ethanol are a result of dissolved salts in the higher water content of this ethanol.

The relatively higher inorganic content of the Brazilian hydrous cane ethanol may not, at first glance, seem like a problem until one considers how hydrous cane ethanol is used in Brazil. Brazil has aggressively developed cars that can operate on either 100 percent ethanol, E85, or E25. In Brazil, both ethanol-only fuel and E85 fuel utilize hydrous ethanol. Anhydrous ethanol is used in E25 gasoline blends because water causes phase separation in these lower ethanol-content blends.

The impact of higher inorganic impurities in hydrous cane ethanol is amplified 3-4 times when ethanol is used neat or as an E85. This is an important consideration for the OEMs developing flex fuel cars.

Haltermann Solutions is an importer of Brazilian ethanol and is ready to assist its customers as they develop vehicles that will operate on hydrous cane ethanol.

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Development of realistic fuel specifications while meeting customer needs and expectations

Thu, Dec 9th 2010, 12:43 by Indresh Mathur

At Haltermann Solutions, we strive to meet our customers’ needs and expectations. This process starts with our customer submitting a custom fuel specification sheet which can be accomplished by submitting the request on-line or by downloading a custom fuel specification sheet and submitting it at the customer’s convenience. This step formally starts the development process to develop a fuel that would meet the desired performance expectations while ensuring our capability to produce the fuel reliably. The next step entails a dialogue with our customer to ensure that the desired specification has taken into account the precision and repeatability (r) of the analytical method used to measure a given specification parameter, the reproducibility (R) among different labs measuring the same parameter and the variability inherent in manufacturing numerous blends of the same fuel.

In an effort to describe the importance of proper specification limits, we have given an example below:

We were asked by one of our customers to formulate a fuel as shown in the specifications given in the attached table. If we had agreed to manufacture this fuel and accepted the specifications proposed by this customer, there would have been a good likelihood that we would not have been able to meet our customer’s needs a percentage of the time. This would happen either because a) certain analytical methods were not precise enough to measure a given parameter or b) the minimum and maximum values expected by the customer were outside the variability of the measurement and the variation of the manufacturing process. To prove our point to the customer, we produced four samples of this fuel in our lab under controlled conditions (manufacturing scale would present additional challenges and variation). Sixteen samples of the same fuel were sent out to 4 different analytical laboratories. Blind analysis (i.e. no specifications or targets provided to the analytical lab) was performed to ensure there was no bias in the results.

Data and results are given below. Statistical analysis was performed on the lab results of the analytical data compiled. You will notice that some parameters proposed by the customer for this fuel were outside the minimum / maximum range predicted by our data or the reported ASTM reproducibility (R) for those methods. These are highlighted in pink color on the attached table. You will also notice that one of the specification parameters (MTBE content) was requested at 0.05%, maximum, whereas the detection limit for the analytical method is 0.2%.
We hope this example has demonstrated to you the importance of proper specification development. We will make every attempt to resolve these issues during our dialog with you regarding your new custom fuel requests. We want to meet your needs but only within our manufacturing and analytical capability to do so.

Click on the table below to view PDF file











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Introducing: Tech Talk!

Mon, Sep 27th 2010, 09:01 by Indresh Mathur

At Haltermann Solutions we strive to provide Solutions to our customer’s fuel needs using our nearly 50 years of expertise in technical specifications development, fuel formulation and blending, and knowledge of the industry’s changing needs.

In this section you can look forward to compelling technical information that will help you understand our capabilities in meeting your needs as well as addressing issues of importance to the industry. In the coming months we will present discussions on a variety of topics including:

  • Development of realistic fuel specifications while meeting customer needs and expectations
  • Computer simulation to speed fuel formulation development
  • Fuel shelf life
  • Differences in corn and sugar cane derived ethanol fuels
  • Unique biodiesel blends made for National Biodiesel Board
  • Ten formulation routes to RP-1 rocket propellant
  • Deposit forming fuels and additives
  • Haltermann’s capabilities to manufacture and procure unique blending components
  • Novel racing fuels
  • Stable fuels for home and garden equipment
  • Unleaded aviation gasoline fuel developments
  • Jet-C aviation turbine fuel

This forum will also give our customers an opportunity to ask us about the technical issues they would like us to address. Please send your requests and ideas directly to me, Dr. Indresh Mathur for consideration.