India's automotive sector is witnessing a significant shift away from diesel engines, particularly in the small car segment. This trend is primarily driven by the fact that diesel engines are considered more polluting than their petrol counterparts. Mounting regulatory pressure and the implementation of stricter emission norms by the government have made developing compliant diesel engines a costlier affair, especially for smaller, budget-friendly vehicles. This is inadvertently steering consumer preference away from diesel.
Why Diesel Engines Emit More Pollutants
The core issue lies in the greater polluting nature of diesel engines. They emit a higher concentration of specific harmful pollutants into the environment compared to petrol engines. The primary culprits are Nitrogen Oxides (NOx) and Particulate Matter (PM), both of which pose significant health and environmental hazards for India's densely populated urban centres.
5 Key Reasons Behind Diesel Engine Pollution
Here is a detailed breakdown of the five fundamental reasons that make diesel engines more polluting than petrol engines.
1. Higher Emissions of Nitrogen Oxides (NOx)
Diesel engines operate using a higher compression ratio, which leads to elevated combustion temperatures. At these high temperatures, the nitrogen and oxygen present in the air react, forming large amounts of Nitrogen Oxides (NOx). NOx is a key component of urban smog and acid rain, and is linked to serious respiratory problems and other long-term health issues.
2. High Particulate Matter (PM) Emission
Diesel fuel is a heavier and less refined hydrocarbon mixture than petrol. During the compression ignition process, this can lead to incomplete combustion in certain zones of the engine cylinder. This results in the formation of soot, known as fine Particulate Matter (PM). These microscopic particles are a major health hazard as they can penetrate deep into the lungs and bloodstream, causing diseases like cancer, asthma, and cardiovascular problems.
3. The Compression Ignition Process
The fundamental way these engines work contributes to the problem. Petrol engines use spark plugs for a uniform ignition of a consistent air-fuel mixture, allowing for more complete combustion. In contrast, diesel engines inject fuel into highly compressed, hot air, leading to a less uniform combustion process. This makes diesel engines more prone to producing PM and unburnt hydrocarbons.
4. Inherent Fuel Composition and Sulfur
Traditionally, diesel contains higher levels of sulfur than petrol, leading to higher Sulfur Dioxide (SOx) emissions. While modern regulations have introduced ultra-low sulfur diesel, the fuel's inherently heavier composition means the combustion process is inherently more complex to manage for all pollutants simultaneously compared to petrol.
5. The Real-World Performance Gap
Modern diesel engines are equipped with advanced exhaust treatment systems like Diesel Particulate Filters (DPF) and selective catalytic reduction for NOx. While these systems yield clean results in laboratory tests, they often underperform in real-world Indian driving conditions. In slow-moving, stop-start urban traffic, these systems may not reach their optimal operating temperature, leading to a significant surge in harmful emissions during filter regeneration cycles.
The combination of these factors explains why the Indian government's push for cleaner air is making diesel technology, especially for small cars, less viable. The higher cost of compliance with new regulations is directly impacting both manufacturers and the choices available to consumers in the market.
