Compressed Natural Gas (CNG) Vehicles: Safety, Efficiency, and Transparency: What We Know!
BY: Ibraheem Muhammad Mustapha
In response to the economic pressures caused by the removal of fuel subsidies and the deregulation of the petroleum sector, the Nigerian government has introduced the Presidential Compressed Natural Gas Initiative (Pi-CNG). This initiative, part of the administration’s palliative interventions, seeks to alleviate the hardships faced by Nigerians by promoting Compressed Natural Gas (CNG) as a cost-effective and environmentally friendly alternative to petrol. The removal of subsidies has led to a sharp rise in petrol prices, making the search for alternative energy sources more urgent. While CNG presents itself as a potential solution with significant economic and environmental benefits, it has also generated a flurry of questions, doubts, and misconceptions among the public.
This explainer by FactcheckAfrica aims to cut through the noise by providing a neutral, evidence-based overview of CNG cars, helping you understand what they are, how they work, and challenges.
What is Compressed Natural Gas (CNG)?
Compressed Natural Gas (CNG) is a type of fuel derived from natural gas, primarily composed of methane (CH4). It is compressed to less than 1% of its standard atmospheric volume, making it suitable for storage in high-pressure tanks and use as an alternative fuel for vehicles. Unlike petrol and diesel, CNG is considered a cleaner-burning fuel, meaning it produces fewer harmful emissions when combusted. As compared to diesel and gasoline, CNG has a longer ignition delay time due to low flame propagation speed. CNG also has lower flame propagation speed as compared to conventional liquid fuels. This lower flame propagation speed reduces the engine brake horsepower by 5–10%. It has been widely adopted in various parts of the world as a cost-effective and environmentally friendly fuel for both private and public vehicles.
How Do CNG Cars Work?
Compressed Natural Gas (CNG) cars operate by utilizing natural gas stored in highly pressurized tanks, which are typically installed in the vehicle’s trunk or under its undercarriage. The natural gas is delivered to the engine through a specialized fuel system that includes a pressure regulator, which reduces the gas’s high pressure to a level suitable for combustion. This gas is then mixed with air and ignited in the combustion chamber, generating energy to power the engine.
CNG vehicles are broadly categorized into two types: dedicated CNG vehicles, which run exclusively on compressed natural gas, and bi-fuel vehicles, which can alternate between CNG and conventional fuels like petrol or diesel. The latter offers flexibility for regions where CNG refuelling infrastructure is underdeveloped. Both systems rely on components such as durable CNG tanks, precise fuel injectors, and an Engine Control Unit (ECU) that optimizes the air-fuel mixture to ensure efficient combustion.
Dispelling Safety Concerns: Is CNG Safe?
While compressed natural gas (CNG) is often touted as a safer alternative to conventional fuels due to its lower flammability, there are valid concerns that need to be addressed, especially in Nigerian context. Some accidents involving CNG vehicles have led to explosions and safety fears. For instance, there have been reports of incidents, including a recent explosion in Edo State, where a fabricated cylinder caused damage and injury. The cause was traced to a non-approved, poorly constructed cylinder, which exacerbates concerns about the safety of CNG conversion. According to a report from The Punch newspaper, one of these explosions led to the loss of life, some injured and property destroyed.
Such incidents, while alarming, are not inherent to the technology but rather indicative of implementation failures. Evidence from other countries highlights the potential for similar issues when safety measures are neglected. In Pakistan, a leading user of CNG vehicles, 55 road accidents involving natural gas vehicles (NGVs) were recorded between 2010 and 2015, resulting in over 250 casualties. These accidents, as study concludes, were largely attributed to unapproved cylinders, misuse of equipment not designed for CNG (such as oxygen or acetylene cylinders), and general non-compliance with safety regulations.
Despite these challenges, available evidence has shown that, CNG, when properly installed, has several safety advantages over traditional fuels like petrol and diesel. Its high auto-ignition temperature of 540°C—compared to 258°C for gasoline and 316°C for diesel—reduces the likelihood of accidental ignition under atmospheric conditions. Additionally, CNG has a narrower flammability range (4.3–15.2% by volume in air), which further lowers the risk of accidental combustion. Unlike liquid fuels that pool on the ground and pose a prolonged fire hazard, CNG, being lighter than air, quickly disperses into the atmosphere in the event of a leak, reducing the potential for fire.
CNG is also non-toxic and does not contaminate soil or groundwater, offering environmental safety advantages over petrol and diesel. While concerns about the availability of certified technicians and proper conversion processes are valid, they are issues of implementation rather than inherent flaws in the fuel itself. Countries with established CNG infrastructure have demonstrated that adherence to international safety standards can virtually eliminate these risks.
Did CNG Reduce the Engine Performance?
The assertion that compressed natural gas (CNG) reduces engine performance has some merit but must be examined in context. According to a study titled Research Progress in the Development of Natural Gas as Fuel for Road Vehicles (1991–2016), the performance of a CNG-powered engine is highly dependent on the engine design and type, whether mono-fuel, bi-fuel, or dual-fuel. However, one notable drawback is the 15–20% loss in brake horsepower compared to conventional petrol engines. This reduction is attributed to factors like CNG’s lower flame propagation speed and its lower volumetric efficiency.
Because CNG is less dense than liquid fuels, it occupies a portion (4–15%) of the intake passage volume, reducing the volume available for air intake. This leads to diminished volumetric efficiency, which impacts power generation. Despite this, advancements in engine design have mitigated these drawbacks, with modern CNG engines achieving power losses closer to 10% compared to gasoline. Such losses may be noticeable in high-performance applications but are less relevant in daily driving scenarios where fuel economy and emissions reduction are more critical, the study conclude.
Transparency Concerns: Are Nigeria’s Safety Standards Adequate?
While the Standards Organisation of Nigeria (SON) has stated that it has adopted some 88 international standards for Compressed Natural Gas (CNG) products to ensure quality and safety, FactcheckAfrica’s investigation revealed that these standards are not publicly available online, raising questions about accessibility and transparency. A simple Google search yielded no direct results or public documents outlining these adopted standards, creating a potential gap in public awareness and trust in the safety of CNG use in Nigeria.
Moreover, there seems to be limited publicly available information about the specific technologies being used to power CNG vehicles in the country. This lack of transparency exacerbates existing safety concerns, especially considering the recent incidents linked to substandard equipment and unauthorized conversions. Without clear and accessible information on the technology and safety standards in place, it becomes challenging to assess whether Nigeria’s CNG systems adhere to global best practices and adequately address all necessary safety measures.
FactcheckAfrica is committed to continuing its search for these adopted safety standards and plans to compare them with international best practices. This comparison will help determine whether they comprehensively cover the required safety measures to prevent CNG vehicle accidents and ensure public safety in line with global benchmarks. Addressing these concerns will be crucial for building public confidence and promoting safer adoption of CNG technology in Nigeria.