Fuel cost savings depend on several factors:

• constant factors: 

  • the density of diesel (0.85 kg/liter) and LPG (0.55 kg/liter).

  • heating value of diesel (43 MJ/kg) and LPG (46 MJ/kg).

• variable factors: the current price of diesel and LPG

Since the efficiency of the converted and the original Diesel-​ engine is the same, if the price of LPG is 0.55/0.85 × 46/43 = 69% of the price of diesel, there is no saving.  If, on the other hand, the price of LPG is much lower than diesel 69%, then it already results in significant cost savings.

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The graph below shows the price savings of diesel fuel after the conversion, for example in the case of HUF 570/liter gas and HUF 275/liter LPG gross fuel prices:

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