One gas good: two gases cooler!
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by Toby Clark • German food retailer Rewe has specified a remarkable reefer in which both the truck and the fridge unit are fuelled by liquefied natural gas (LNG)—and propane is used as the refrigerant.
The MAN 19.233 with a Schmitz body is fitted with a spark-ignition engine and a Messer LNG fuel system. But the refrigeration system, suitable for temperatures down to -35°C, is even more unusual: it is basically a Ftigoblock FK13 unit (its most popular type) converted to use natural gas as a fuel and propane as a refrigerant.
Propane is inexpensive and has no ozone-depleting effect, so it does not contribute to global warming, unlike HFCs such as R404a and R134a, both of which are widely used in domestic and industrial systems.
A potential problem is that propane is highly flammable. But the vehicle is already approved to use natural gas (methane), and has gas sensors. The fridge unit is modified to prevent leaks, with no detachable pipe connections--all pipes are welded or brazed. Electrical components are uprated and sealed to avoid spark generation.
The liquid fuel is stored at -161°C, and must be evaporated for use in the engine. This is done via a heat exchanger in the load compartment, reducing the fridge unit load by 25-30%.