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Cat : How to Fairly Compare Fuel Consumption

Jun 7, 2022 | Special Application | 0 comments

Diesel generator set manufacturers publish fuel consumption (VFC) data in volume units in their specification sheets. A problem arises when trying to compare vfc data from different manufacturers. Fuel density, brake fuel tolerances and fuel calorific value all affect fuel consumption. To fairly compare vfc data between manufacturers  , some adjustments need to be made to match another set of parameters.

Cat C9 to C175 diesel generator sets vfc are engine-based fuels with nominal power and 35° API (16°C or 60°F) with an LHV (low calorific value) of 42780kJ/kg (18390Btu/lb) when at 29°C (85°F). F) the density is 838.9 kg/m³.

Based on the fuel consumption of the nominal power, he Caterpillar VFC has a tolerance of +/-3%.

However, many manufacturers’ VFC data are based on ISO3046-1 and cite “unless otherwise noted, the fuel consumption of the declared power is allowed to increase by 5%”. This enables manufacturers to reference vfc data with tolerances of 0 to +5%,  that is, the published vfc data is the best and can be +5% tolerant.

Caterpillar vFC data is conservative and, therefore, cannot be directly compared with manufacturer data citing ISO3046-1. For a fair comparison, Caterpillar vfc data can be adjusted to data with +5% tolerance. Figure 1 below shows a comparison of fuel tolerances, with reported values expressed as red dots.

To adjust the Caterpillar vfc, first multiply the nominal value by 1.03 to find the maximum possible value equal to ISO3046 +5% (maximum), and then you must divide the value by 1.05 to find a new nominal value with a tolerance of +5% for ISO3046. The new adjusted Caterpillar nominal values are represented in Figure 1 with a red dotted circle.

Many manufacturers typically use a fuel density of 850kg/m³, which is higher than the 838.9kg/m³ referenced by Caterpillar, which also helps to obtain more favorable VFC data. It can also be counted in the adjustment calculation:

Adjusted Cat VFC (ISO 3046)

= Cat VFC * 1.03 / 1.05 * (838.9 / 850)

≈ Cat VFC * 0.96814

The equation above shows that the vfc data displayed on the Caterpillar spec sheet  is multiplied by 0.96814 to produce data that can be compared with data from other manufacturers that reference the ISO3046 standard. Note from Figure 1 that the adjusted Caterpillar VFC still has the potential to outperform the reported values due to the large tolerance band.

0.96814 This correction factor reflects the ISO3046-1 standard. However, it is important to recognize that the correction factor may vary depending on the fuel specification chosen by the manufacturer, such as different LHVs.

It is impractical to try to account for all changes in fuel specifications, and customers should check the manufacturer’s specifications to find the fuel density and LHV value used. If this value is found to be different from 850kg/m³ (or g/l) and 42780kJ/kg, different correction factors are required.

The correction factor for Caterpillar vfc data can be calculated as follows:

Correction factor = 1.03/1.05*(838.9/A)*(42780/B)

A = Fuel density published by the manufacturer in g/l or kg/m³

B = Manufacturer’s published low calorific value (LHV) in kJ/kg

The customer should then calculate the adjusted VFC (ISO3046) based on the calculated correction factor.

Adjusted VF (ISO3046) = Cat VFC* correction factor

Through this article, we have introduced you how to fairly compare fuel consumption values between different manufacturers, where calculation standards are very important. Although diesel generator sets usually do not need to operate power supply, when an emergency occurs, the use of diesel power supply may take several hours, dozens of hours, or even days, dozens of days to support the normal operation of your facilities. This is the key moment to test the fuel consumption of the unit. If your project is strict about costs, it is critical to correctly select products with lower fuel consumption.


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