We all know CNG cars were introduced in India mainly because it is considered to be a cleaner fuel than petrol. And the side benefits? When CNG was launched in the early 2000s, it was much cheaper than petrol and offered higher mileage. Sounds fair. But have you ever wondered why we see CNG petrol cars but no CNG diesel ones? Come to think of it, a diesel-CNG combination can offer even higher mileage! So why don’t we see it in passenger cars? Here’s a look.Attention Readers! Join us on our WhatsApp Community for daily auto news updates.
Diesel-CNG Technology Does Exist Commercially
It’s not like no one has thought about it before. You’ll find CNG-diesel dual-fuel systems in commercial vehicles, buses, trucks and some retrofit applications. Since these vehicles have higher annual mileage, the fuel savings can justify the additional hardware. Mainstream Indian commercial vehicle brands do offer diesel-CNG bi-fuel models.
Diesel + CNG is Possible, But Tricky.
Unlike petrol, a regular diesel engine does not use a spark plug to ignite fuel. Diesel engines ignite fuel by high-temperature compression. CNG has a high-octane rating and is difficult to ignite through compression alone. CNG works in a petrol engine because the spark plug can ignite the compressed gas exactly when needed. A diesel-CNG engine generally needs a small quantity of diesel to act as a pilot fuel. So, technically, a CNG-diesel engine cannot operate on CNG alone. It means you haven’t really created a conventional “diesel-CNG” car. You’ve created a dual-fuel engine.
Also Read: Petrol vs CNG vs Diesel vs Hybrid: Which Makes More Sense?
Diesel-CNG Cars: Key Problem
To make a diesel-CNG passenger car viable, the manufacturer would have to add a CNG storage system, high-pressure fuel lines and regulators, a complex dual-fuel injection/control system, a diesel injection system, sensors and calibration for two fuels, more complex emissions after-treatment, and additional safety engineering. That means more hardware, which can’t be packaged in a vehicle the size of a passenger car. Moreover, since CNG has lower energy density by volume, a passenger car will need a fairly large, heavy tank to carry enough energy for meaningful range.
This is why this system makes sense and is viable in a vehicle the size of a large commercial one.
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The Ultimate Problem
Price. Compared to petrol, diesel engines are already more expensive to manufacture because of additional hardware, including current BS6 equipment such as a DEF tank, diesel particulate filter, etc. Adding CNG hardware to an already expensive diesel powertrain makes the additional investment hard to justify in a small passenger car.
Diesel-CNG Cars: Regulatory Challenges
Modern diesel passenger cars already have increasingly expensive emissions-control systems because of stringent regulations. Adding CNG will not eliminate those requirements because the vehicle still burns diesel as pilot fuel. So, manufacturers would spend heavily to develop and certify a technology for a relatively small potential market.
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