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Compressed natural gas – diesel dual fuel option adds value to truck range

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FUEL consumption is the biggest operational cost in any truck fleet. Addressing this issue with a Compressed Natural Gas – Diesel Dual Fuel (CNG-DDF) option for 20 Isuzu models, Isuzu Trucks now offers strategic fuel solutions for reliable, cost-effective, and consistent mobility.

Automotive use of CNG is a proven technology – up to 14 million Natural Gas Vehicles (NGVs) operate in 80 countries worldwide. Isuzu Motors South Africa (IMSAf) has been testing a fleet of CNG-DDF converted trucks for five years with proven reliability.

CNG is not to be confused with ‘Liquified Petroleum Gas (LPG) used for flame-grilled steaks! Unlike LPG, CNG is lighter than air. In case of leakage, CNG disperses quickly in the atmosphere with low risk, while LPG spreads on the ground and poses a high risk of ignition. CNG has less carbon thus produces lower volumes of carbon monoxide and carbon dioxide during combustion. Consequently, CNG is a better and safer option than LPG.

Environmentally acceptable

Supporting the challenge to be green, the use of CNG has the following advantages:

  • Reduction in Carbon footprint – cleaner fuel – NGVs emit 20-25% less greenhouse gases and virtually no toxic pollutants.
  • Reduction in particulates.
  • Reduction in Engine noise thanks to natural gas’ smoother combustion.
    Reduction in fuel consumption.
  • Reduction in fuel theft and adulteration.
  • Less engine carbon deposits leads to a longer engine life.
  • Improved engine oil quality due to reduction of carbon emissions.

Isuzu’s CNG-DDF is easy to operate

The diesel cycle engine remains in standard execution with 100% fallback to diesel at any time. By simply pressing a button, operation switches between dual fuel mode (diesel/gas a mixture) and 100% diesel mode. Operation automatically reverts to 100% diesel mode when the natural gas cylinder is empty or when a fault is detected with the CNG system.

There is a quick gas filling time compared to charging times for electric trucks. But driver training is still necessary.

Trip times & performance

Engine performance and efficiency is maintained in dual fuel mode – engine torque and power remain practically the same. Trip times are unaffected. The engine works with diesel and CNG simultaneously – a special engine control unit determines the optimal gas/diesel fuel mixture. With similar torque and power, trip times are unchanged.

Safety considerations

CNG is lighter than air and will disperse harmlessly into the atmosphere – an odorant is added for safety and easy detection. The gas has a narrow range of flammability and ignites at concentrations of between 5% and 15% (petrol = 1-8%). It has a statistically proven safety record which is superior to conventional fuels and is non-toxic.

With the coastal price of diesel fuel at R21,91/litre – a diesel tank of 400 litres cost nearly R8800. While Brent Crude hovers around US$84 a barrel, the Middle East and European wars present weekly crises and the oil price is volatile. All of this means that fuel, and CNG in particular, should be a strategic – and not just a price – consideration.

The challenge for CNG is the distribution network. Municipalities are an ideal application from an environmental, fuel consumption, anti-theft, and centralised refilling viewpoint. CNG is currently only available in the Gauteng region. The CNG gas cylinders mounted to a Dual Fuel truck add to the tare mass and reduces payload – GVM and GCM remain unchanged.

CNG gas cylinders need chassis space making the conversion to CNG-DDF more suited to long wheelbase models.

The fact that it can be fitted as an option to 20 Isuzu long wheelbase models is a huge advantage for fleet replacement planning. The TruckScience Axle Weight Calculator, available from, is a valuable tool for understanding the implications of the added weight of the CNG equipment, and for calculating payload capacity.

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