Diesel Flash Point Study 2c4c6p

2004-28-0078

Significance Of Flash Point in Diesel Fuel Specification A.R. Arankatle, V.G. Kenjale, tfi.K- Chaudharl and B. Bhanot The Automotive Research Association of India, Pune INTRODUCTION Consequences of ambient air quality on human health is the major driving force to implement stringent vehicular emission norms and the related fuel quality specifications. In addition, engine technology & aftertreatment devices, vehicle maintenance practices, driving pattern and road conditions also contribute to ambient air quality and emissions of toxic hydrocarbons & gases that affect human health. The diesel fuel quality in this regard is of the major concern than gasoline as it constitutes about 38% of the total consumption of petroleum products in automobiles in our country. Diesel demand is thus higher by about SVi times than gasoline whereas in other countries gasoline demand is higher than diesel. To improve fuel quality, the Govt, of India constituted a committee of experts of National repute to formulate an Auto Fuel Policy for the country together with a road map for its implementation. Investment of about Rs. 10,000 crores has been made in last decade for gasoline and diesel quality improvements. The major milestones achieved in diesel quality improvements from 1994 are as follows: •

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Sulphur content has been reduced by 75% from 1% max. in 1996 to 0.25% max. in entire country from 1.1.2000. In addition, in the four metro town sulphur content has been reduced by 95% to 0.05% max. To improve ignition performan9e of diesel engines and lower pollutant emissions, Cetane number, has been increased from 45 to 48 from 1.4.2000. Improvement have been done in the distillation specification by 1.4.2000 thereby improving performance, life of. diesel engines and emission reduction Irrespective of these improvements, many milestones have yet to be achieved in fuel quality to further meet Euro-Ill and Euro-IV emission norms which will be implemented in 10 major metropolitan cities by year 2005 and by 2010 respectively. For the rest of the country Euro-Ill norms will be implemented by year 2010. To achieve these targets, the Indian standard IS: 1460-2000 on diesel fuel needs to be stream-lined with the Euro / EPA fuel quality specifications ancf follow World Wide Fuel Charter (WWFC) guide-lines. Some of the major fuel characteristics that need to be addressed

to achieve demands of vehicle manufactures to meet Euro-Hl and Euro-IV norms are: • Control on density and viscosity within narrow range • Raise the Flash Point of Fuel with respect tc tropical conditions in India • Control aromatics and in particular the Poly Aromatic Hydrocarbons (PAH) in fuel. • Bring down the sulphur contents • Mandate on Multi Fuel Additives to improve lubricity, Cetane number, storage stability, engine cleanliness, etc. One of the fuel parameter that is of concern is Flash point of diesel fuel which is 35°C minimum as per IS: 1460-2000. To demonstrate its importance and significance from safety, engine performance and emission point of view in Indian context, The Automotive Research Association of India, Pune (ARAI), did experimental study. The present paper discusses on results, observations and provides guidelines on concern subject to improve fuel quality. WORLD-WIDE SCENARIO OF FLASH POINT SPECIFICATIONS By definition, Flash Point is the lowest temperature at which vapours above liquid will ignite when exposed to a flame or any other ignition source with sufficient energy. It is a measure of both volatility and flammability. In case of diesel fuel it is set by its distillation parameters. Internationally, the petroleum products are classified for flash point according to CCE and NFPA norms based on their volatility and flammability nature (Table-1).

The Flash point of Indian commercial diesel fuel is categorized based on CCE classification and falls under Class B, which is equivalent to Category I as per NFPA norms. The regulations in the Federal Republic of (FRG) follow DIN 51755 for flash point of diesel and thus define its importance for storage and transportation with respect to combustibility of liquid fuels. It distinguishes between Danger Class Al (Flash point below 21 °C), which includes Spark Ignition Engine Fuels, Danger Class All (Flash point 21 to 55°C), to which kerosene belongs and Danger Class AIM (Flash point over 55 to 100°C) which includes diesel fuels. Worldwide Fuel Charter and European countries specify the flash point of 55°C minimum. The Australian and New Zealand standard limits are 61 °C min. The Japan specify 45 or 50°C depending upon the climatic conditions. Other European and Asian countries also specify higher flash points as shown in Table-2.

However, the Indian standard (13:1460-2000) is an exception and recommends 35°C minimum flash point value due to the economic yield associated with fuel quality available in the country. Moreover, Auto Fuel Policy document also states that the property has no impact on engine performance because the auto-ignition temperature of the fuel-air mixture is not affected by variations in flash point.

EXPERIMENTS ON DIFFERENT FLASH POINT DIESELS AND CO-RELATION WITH OTHER IMPORTANT FUEL PARAMETERS To signify the importance of flash point of diesel fuel primarily from safety point of view and secondarily from the associated emissions The Automotive Research Association of India, Pune conducted experiments on diesel fuels having flash points from 40 to 80°C. In the experimental work the fuel parameters that are related with flash point were studied along with fuel chemistry, air-fuel ratio and oxygen content. It also includes analysis of fuel for density, viscosity, distillation recovery, pour point, cold filter plugging point (CFPP) and lubricity - the parameters that are specified in the Indian standard. The diesel fuel is a complex mixture of hundreds of individual compounds with carbon number between C10 to C22. These hydrocarbon compounds makes difficult to separate out the naphtha, kerosene, diesel and heavy oil fractions that makes the diesel fuel. According to the literature, based on carbon numbers the naphtha, kerosene, diesel and heavy oil fractions in the petroleum products are classified as shown in Fig. 1. It can be seen that they overlap each other.

Hence, in the ARAI experimental work, the hydrocarbons were splitted into fractions based on carbon number as follows :

The High Resolution Gas Chromatograph (HRGC) was used to analyze these fractions in fuel using Detailed Hydrocarbon Analysis (DHA) software.

tank is filled with 10, 25, 50, lb % by volume of tank capacity and heated from room temperature to 55°C. The aim and objective of this experiment was to ascertain the effect of variable ambient temperature conditions on volatility and flammability of diesel fuel having different flash point values.

An experimental set up (Fig.2) was designed to determine the effect of diesel fuel flash point on air to fuel vapour ratio and oxygen content when the fuel

The experimental results are summarized in Table-3 and Fig.3 to 5. OBSERVATIONS RESULTS

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COMMENTS

ON

TEST

Density, viscosity, distillation recovery at 350°C and 370°C meet the Indian specification for all flash point diesel fuel samples. However, experimental results show following observations on diesel fuels with different flash point values. •

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As per the literature, for combustion to take place at room temperature and propagate the flame for hydrocarbon-air mixture, the relative air to fuel ratio (actual fuel-air ratio divided by stoichiometric or chemically correct fuel-air ratio) should lie between 0.5 to 2.1. This ratio is known as "lambda value". In

the experiment, it is found that fuels having 43°C and 48°C flash point are in the vicinity of lambda value 2.1 (rich end of the scale) as fuel tank temperature is raised (Fig.3). It means that fuels

with low flash point are more prone to catch fire and propagate the flame in presence of external ignition source when compared with high flash point fuels (e.g. FP 68°C & 80°C).

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Based on these observations, 35°C min. flash point diesel fuel may be more dangerous to lead to tank explosion and propagate the flame for the typical tropical conditions as seen in India. Particularly this phenomenon occurs where two vehicles collide with each other or when propeller-shaft fails and rams into fuel tank. Many of such accidental cases are reported in past in newspapers where occupants in the vehicle burned to char within no time to escape out of the vehicle. Such accidental cases lacked in the systematic investigation and analysis of flash point of fuel with respect to air to fuel vapour ratio that exists in the fuel tank and surrounding ambient temperature conditions to our observations. The distillation recovery curve (Fig.4) shows that with increase in flash point of diesel fuel, the Initial Boiling point (IBP) also increases

35 to 42% and fractions.

balance

should

be

diesel

CONCLUSIONS • •

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from 137°C to 201 °C. According to available literature, increase in IBP from 175°C to 210°C reduces NOx by 12%, HC by 40% and PM by 24% (see Table-4). The results are thus indicative that flash point affects distillation curve and especially the IBP and in turn has significant effect in meeting the emission norms. The Fig.5 is indicative that fuel constituents also affect the flash point and IBP of diesel fuel. Decrease in Naphtha fractions and increase in diesel & kerosene fractions in diesel fuel increases the flash point of fuel. As per Bosch Automotive Handbook, less than 3% gasoline (in present discussions referred to as Naphtha) in diesel fuel is sufficient to lower the flash point to such an extent that ignition becomes possible at room temperature. In reality, thus, naphtha fractions should be absent in the diesel fuel. The presence of naphtha also increases the static electricity associated with the fuel and can act as source of ignition. In neat diesel, the literature survey also shows that kerosene (C 9 to C15) content vary between

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Indian diesel fuel needs control on naphtha fractions (< C9) to 5% max. To reduce the reported accidental cases where occupants are burnt to char due to explosion of fuel tank when vehicles collide with each other it is essential to increase flash point of diesel from 35°C to 55°C minimum irrespective of loss in economic yield from safety point of view. Raising of flash point also increases the IBP of fuel and significantly reduces the CO, NOx and PM in vehicle exhaust to meet the emission norms that auto industry has to meet in the future. Increase in flash point will reduce menace of adulteration practices with abuse of solvent/spent naphtha, used oils, spent solvents, low grade kerosene and diesels, etc. Thus, monitoring of flash point is a better tool than filter paper test and density measurement in the field. With the world trend to move towards low sulphur fuels, there are some concerns about conductivity. Low flash point diesel fuel with higher naphtha fractions (light distillate) could become an increasing concern. Gas chromatography techniques if adapted in the specification can help in adulteration studies.

Thus, the overall conclusion is that Indian specification on Diesel fuel should be revised for the flash point value considering its relative impact on safety and consequently on CO, NOx and PM emissions from vehicle exhaust to be in line with International specifications. Probably, to our knowledge the flash point may act as a fuel parameter to identify adulteration practices along with density measurement.