Which Fuel Type is Best for your Business

Jul 08, 2013

Now that you're replacing your fleet, the decision needs to be made on whether to settle on a gasoline or diesel powered fleet. Rather than just jumping in and saying that one or the other is the superior choice, it's important to know the differences between the two engines aside from what goes into the tank.

Difference between Diesel and Gasoline

Right from the start of the refinement process, distinctions emerge that set both combustion systems far apart in the eyes of a consumer.  At the turn of the century, diesel engines were noisy, aggressively vibrational and released a cloud of noxious exhaust. However, many of these drawbacks have been reduced since, while still being able to retain the advantages that originally piqued consumer interest.

The primary distinctions that most consumers focus on in regards to these two options is price at the pump and fuel efficiency. Understandably so because these are two of the most prevalent topics in today's petroleum driven economy.  In terms of diesel, consumers are seeing a higher price at the pump than "regular unleaded" and in many areas higher than "premium unleaded" as well.  While this can be a breaking point for a fleet manager who is purchasing 1000 gallons a month, the 11% increase in energy output that diesel provides generally offsets this price difference due to the distance allowed between fill-ups. 

This price dichotomy is additionally negated by the method of fuel-injection that is utilized in diesel engines; diesel is injected directly into the cylinders rather than being mixed with incoming air within the intake manifold.  Direct fuel-injection causes little fuel to be wasted in the down-stroke of combustion.

Then, if hauling heavy weight is necessary, direct fuel-injection combined with lack of spark plugs create a high torque environment that often doubles the lb-ft output of gasoline. The aforementioned higher energy output is due to the higher energy density of diesel which leads to a high compression ratio (17:1 for diesel versus a 9:1 ratio for gasoline). Which means that diesel creates low-end torque, while gas creates high-end power. An example of this is clearly seen with comparing a market leader's 5.7L V8 gas engine to one of its 6.7L I6 turbo diesel blocks. The former produces 383 Hp and 400 lb-ft of Torque at 5,600 RPM while the latter puts out only 385 HP at 2,800 RPM but an astounding 850 lb-ft of Torque at 1,600 RPM.

However, this high-compression ratio and torque output has one downside that is possibly offset by longevity. All of the pressure that is produced in a diesel system has a detrimental effect on the internal components; cylinder heads, shafts, block, pistons, and valves.  Beefing up these parts creates a significant weight and price difference from the gasoline options.  Choosing the 6.7L diesel from the above example is a $7,795 price increase for the engine alone; an additional $2,650 is needed for the transmission swap.  Yet, because the internal structure has greater support, a diesel engine can be expected to last more than 200,000 miles on the low end of the spectrum, creating more time between vehicle replacement schedules.

As a fleet manager, deciding on which vehicles are being utilized is just as important as who is driving.

The Better Fuel Solution?

Does your company earn profits through quick trips around a small region without hauling much of a payload, and need to keep fuel costs at a minimum? Choosing a gas fleet should be strongly considered, because of the easily accessible, cheaper and cleaner fuel and smooth acceleration. However, if fuel economy is important even if it means spending a bit more in the short term and long distances are travelled towing heavy loads on a regular basis then it is recommended that a diesel fleet be your next selection. This is because of a diesel engine's greater fuel-efficiency, high torque and extended life span. Remember, saving a few bucks in the beginning might end up costing your company a fortune through the life of a fleet.