Another way to make power, but is
it practical?
By
C.J. Baker
Systems
for injecting propane into turbo-diesels have been around
for some time. The people that make and sell such systems
claim that diesels only burn about 75 percent of the fuel
that is injected into the cylinders, and that propane acts
as a combustion catalyst to burn the remaining 25 percent
of the fuel. This is a dubious claim, especially for newer,
modern diesels. Direct injection and common rail fuel injection
greatly improve the efficiency of turbo-diesel combustion
while simultaneously reducing emissions. If 25 percent of
the fuel were going out the exhaust unburned, modern diesels
would have high hydrocarbon and particulate emissions. In
truth, they have neither. The same cannot be said for older,
indirect injection (IDI) diesels, which are less efficient
than “modern” configurations, but it is doubtful
that even IDI diesels waste 25 percent of the fuel injected
(see "Diesel
Evolution" elsewhere on this site).
Purveyors
of propane systems also claim fuel economy will increase
2-3 miles per gallon with full-time use of propane injection.
They make no distinction between motorhomes and pickups,
but since they probably want to portray as favorable a number
as possible, we must assume that increase is for an unloaded
pickup. While this claim may be accurate, it is also misleading.
What’s really important is the total fuel cost per mile,
which isn’t just the diesel fuel costs, but also the
propane costs. Most propane systems use approximately one
gallon of propane to every four gallons of diesel fuel. When
the propane cost is added in, it’s often cheaper to
get the lower miles per gallon on straight diesel without
propane.
Of
course, propane systems aren’t sold purely for fuel
economy. Most propane systems are sold to add power to the
vehicle. There’s no argument here. Propane will add
power to help negotiate long grades, shorten passing time,
etc. How much power is added depends on the system design
and the size of the turbo-diesel it is used on, but 50 to
100 HP gains are commonly advertised. Propane proponents
also suggest a high-flow performance exhaust system be added
to the vehicle to realize the full power potential of a propane
injection system.
At
Banks, we think there is a better and safer solution to adding
power and economy. A propane system, propane tank, refill
kit, and performance exhaust system can easily cost $1800
to $2500, and in truth, much of the power and economy gain
may be coming from the high-flow exhaust system. A better
plan is to add a power system that increases total engine
airflow and efficiency. Banks has a range of such power systems
from the economical Git-Kit to the top-of-the-line PowerPack®
for most turbo-diesel pickups and motorhomes. The beauty
of this approach is that power is increased as much or more
than by adding propane, fuel mileage is improved (and total
fuel costs reduced), there’s no need to buy or refill
a propane tank, and there’s no potential hazard of carrying
flammable propane. Better still, a Banks system lowers exhaust
gas temperature and extends engine life. In the long run,
a Banks system is less expensive, more efficient, safer,
and more convenient.
For
maximum power rigs, such as those used in pickup pull or
truck pull contests, or even diesel light truck drag racing,
propane injection can be used as a way to further increase
power on a diesel that has already been extensively modified,
especially if it been modified to the point of overfueling.
However, under these same circumstances, we believe equal
or greater power gains can be achieved with less expense
and trouble by installing nitrous oxide injection (see "Nitrous
Oxide & the Diesel" elsewhere on this site).
The
bottom line: save the propane for the stove and the furnace.
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