By Otsile Kadiege

Fuel consumption is one of the biggest operational costs in any truck fleet. In a bid to reduce these costs, Isuzu Motors South Africa believes Compressed Natural Gas – Diesel Dual Fuel (CNG-DDF) will address this issue. Isuzu Motors South Africa has been testing a fleet of CNG-DDF converted trucks for the past 5 years and will be available as an option for 20 of the automaker’s models. This places Isuzu trucks at the top of a volatile fuels market in offering strategic fuel solutions for reliable, cost-effective, and consistent mobility. Automotive use of CNG is a proven technology – up to 14 million NGVs (Natural Gas Vehicles) operate in 80 countries worldwide. 

Differences between CNG and LPG

CNG (Compressed Natural Gas) & LPG (Liquified Petroleum Gas) fuels are different. While CNG consists of methane, LPG includes propane and butane. CNG is typically used as a substitute for petrol / diesel in automotive applications, while LPG is often used in industrial, refrigeration, agricultural and catering industries.

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 high risk of ignition. CNG has less carbon thus, producing lower amounts of carbon monoxide and carbon dioxide during combustion. Consequently, CNG is a better and safer option than LPG.

Environmentally acceptable

The use of CNG has the following advantages:

1) Reduction in Carbon footprint – cleaner fuel – Natural Gas Vehicles (NGVs) emit 20-25% less greenhouse gases and virtually no toxic pollutants.
2) Reduction in Particulates 
3) Reduction in Engine noise thanks to natural gas’ smoother combustion.
4) Reduction in fuel consumption
5) Reduction in fuel theft and adulteration
6) Less engine carbon deposits = longer engine life
7) Improved engine oil quality due to reduction of carbon emissions.

Operating an Isuzu CNG-DDF truck

1) The diesel cycle engine remains in standard execution with 100% fallback to diesel at any time.
2) Simply pressing a button, switches between Dual Fuel mode (Diesel/Gas mixture) and 100% Diesel mode.
3) Automatically reverts to 100% diesel mode when the natural gas cylinder is empty or when a fault is detected with the CNG system.
4) Quick gas filling time compared to lengthy charging times for electric trucks.
5) Driver training is still necessary.

Trip times & performance

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

Safety Rules

1) CNG is lighter than air and will disperse harmlessly into the atmosphere – an odorant is added for safety and easy detection.
2) CNG has a narrow range of flammability – ignites at concentrations of between 5% and 15% (petrol = 1-8%).
3) Statistically proven safety record – superior to conventional fuels.
4) CNG is Non-Toxic.

The coastal price of diesel fuel is 21,91/litre – a diesel tank of 400 litres cost nearly R8800. While Brent Crude hovers around 84 USD 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 TruckScience.com, is a valuable tool for understanding the implications of the added weight of the CNG equipment, and for calculating payload capacity.