Once the villain of India’s pollution story, diesel is making a cautious return to respectability—armed with cleaner tech, stronger regulations, and a heavy dose of real-world pragmatism.
09 Apr 2025 | 831 Views | By Shahkar Abidi
In the dull winter of the mid-1990s, Delhi's air turned from a nuisance to a national emergency. A heavy, pungent haze lay suspended above the capital, smothering the city. As lung-clogging smog became the new normal, a fierce debate erupted in courtrooms, in the media, and in the offices of ...
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In the dull winter of the mid-1990s, Delhi's air turned from a nuisance to a national emergency. A heavy, pungent haze lay suspended above the capital, smothering the city. As lung-clogging smog became the new normal, a fierce debate erupted in courtrooms, in the media, and in the offices of automakers. The culprit—or at least, the most visible one—was diesel.
A proposal by the Environmental Pollution (Prevention and Control) Authority (EPCA), an autonomous body, jolted the nation’s automotive industry. It suggested a full ban on diesel-powered private vehicles in the National Capital Region. What it meant in clear language was that for cleaner air, the diesel had to go. But the auto industry—India’s technological and economic workhorse—had other ideas.
What followed was not just a public policy reckoning, but the beginning of a long, complicated love-hate relationship between India and diesel.
A War of Engines
Tata Motors, known then as Tata Engineering and Locomotive Company (TELCO), was among the first to publicly challenge the proposed ban. But theirs wasn’t a flat-out denial. Diesel, they admitted, was no saint. But the issue, they argued, wasn’t just the fuel. It was how the fuel was burned—and how well regulators enforced standards. With the right combustion technology and emissions control, diesel could rival or even outperform gasoline in certain environmental metrics. Diesel engines, after all, were more fuel-efficient. They consumed less, emitted less CO₂ over time, and offered better mileage—a tempting combination for a fuel-starved economy.
The Supreme Court, often the final arbiter in India’s environmental affairs, took the industry’s point. Rather than issue a sweeping ban, it took a different path. In 2000, Delhi became the first Indian city to adopt Bharat Stage II (BS2) emission standards—similar to Europe’s Euro II norms. It was a signal: India would pursue cleaner tech, not blanket bans. Today, that decision looks prescient.
The Transition Into a Cleaner Fuel
Fast forward to 2024. At a panel discussion titled “The Future of Diesel,” hosted by Autocar Professional in collaboration with the Tamil Nadu government, the story came full circle. On stage sat Rajendra Petkar, President and Chief Technology Officer at Tata Motors, reflecting on a decades-long journey.
“So from where it started with the pre-BS1, with a certain profile of the emissions, to now, the, you know, the BS6. There is a significant cleaning that has happened as far as the tailpipe emissions are concerned,” Petkar said, noting that today’s diesel engines meet Bharat Stage VI (BS6) norms—equivalent to Euro 6 in Europe, among the strictest globally.
Alongside him were R Velusamy of Mahindra & Mahindra, Harshad Jambaulikar of Infineum India, and Viswanath B of Delphi-TVS Technologies. The panel discussion was moderated by Hormazd Sorabjee, Editor, Autocar. Together, they made one point clear: diesel isn’t going anywhere. Not yet.
India’s transportation sector, for all the headlines around electrification and alternative fuels, still runs—quite literally—on diesel. And according to many experts, it will continue to do so for the next decade or more. That makes innovation not optional, but imperative.
The Technology Tipping Point
Modern diesel engines are marvels of engineering. Clean, efficient, and regulated down to the molecule, they’ve come a long way from the soot-belching blocks of the past.
Tata’s recent accomplishment with its compact SUV, the Nexon, is illustrative. Instead of opting for the industry-standard Selective Catalytic Reduction (SCR) system—a complex method involving urea injections to neutralize NOx emissions—the company chose a simpler, leaner path: the Lean NOx Trap (LNT).
In theory, LNT systems are best suited for smaller, less powerful engines and work optimally when exhaust temperatures stay below 400°C. This temperature threshold, however, becomes difficult to maintain in Indian stop-start traffic conditions. Tata’s engineering team tackled the problem at the root: tweaking base engine components, fine-tuning performance software, managing turbo boost, and aligning thermal behavior—all to keep temperatures low while still meeting BS6 Phase 2 standards.
The result? A low-cost, technically elegant solution tailored to Indian driving patterns.
Local Lessons, Global Technologies
Viswanath B, CTO at Delphi-TVS, emphasizes a key point: context matters. Western diesel systems are built for high-speed highway driving. But in India—where urban speeds rarely break into higher speeds —those models often underperform. When a customer couldn’t decide between SCR and LNT, Delphi-TVS tested both under real-world conditions. LNT won. It wasn’t just cheaper—it was better suited to the job.
This emphasis on India-first solutions is growing. Viswanath believes that while Bharat Stage VII (BS7) norms are still being debated, it’s the incoming WLTP (Worldwide Harmonized Light Vehicles Test Procedure) expected around 2027 that will be a game-changer. The WLTP focuses on real-world performance, making lab-based emission results less relevant. “So, I think now from henceforth, whether it is for the WLTP or for the PS7, whether there is going to be a significant cost increase on the diesel, the answer is really no" he said.
Mahindra’s Diesel Bet
Back in 2017, when diesel was still reeling from the global "Dieselgate" scandal—Volkswagen’s manipulation of emissions controls—Mahindra made an unorthodox move. While global automakers were scaling back diesel investment, Mahindra doubled down. The company poured Rs 4,000 crores into developing a new family of diesel engines.
R Velusamy, President, Automotive Tech & Product Development at Mahindra & Mahindra, doesn’t regret the bet. “Clearly we are seeing the results of that,” he said. Mahindra’s diesel SUVs remain market leaders, and the new engine family is already ready for BS7.
But Velusamy is pragmatic. Diesel is increasingly a powertrain for bigger vehicles. “For smaller vehicles, the cost disadvantage just doesn’t make economic sense,” he noted. Regulations like CAFE (Corporate Average Fuel Efficiency) are harder on diesel engines, driving up costs. As a result, small diesel cars are disappearing.
The company is also preparing for Euro 7’s ripple effects. Unlike previous norms, which focused on outputs, Euro 7 (and by extension BS7) will focus on continuous emission monitoring. Onboard Performance Monitoring (OPM) will require vehicles to constantly track emissions and report anomalies. This adds layers of complexity.
Velusamy sees a shift from measuring larger PM (particulate matter) sizes like PM23 to smaller ones like PM10. This will push engineers to develop better Diesel Particulate Filters (DPFs), which in turn could create problems like higher back pressure.
But for the average Indian SUV with a 1.5L engine, Velusamy expects evolutionary—not revolutionary—changes. “Efficiency improvements in the intercooler, turbocharger, fuel systems, and software will do the trick,” he said.
The Oil in The Machine
The clean diesel story isn’t just about combustion—it’s also about lubrication. Harshad Jambaulikar, representing Infineum India, explained the quiet but crucial role of lubricants in meeting modern emission norms. Historically, oil was about protection. Today, it’s also about emissions.
Lower viscosity oils improve fuel economy but traditionally compromise durability. The fix lies in chemistry: better additive packages that provide protection with thinner films. These additives also play a role in protecting DPFs. High ash content in oils can poison the sensitive metals in filters. Newer lubricants now legally limit ash content and are custom-built for specific engines.
“The jump from BS4 to BS6 was the real cost climb,” Jambaulikar said. Going forward, he expects manageable refinements—nothing on the scale of past leaps.
The Road Ahead
If diesel’s story once looked like a slow death, it now resembles a cautious revival. Cleaner than before, cheaper than high-voltage alternatives, and more suited to the demands of India's vast and varied geography, diesel is adapting—and surviving.
Yet perception lags behind technology. Diesel still bears the burden of its past: the smog-choked winters, the courtroom bans, and the global scandals. Changing this narrative, the panellists argue, is the industry’s responsibility. “We need to educate—not just customers, but policymakers and influencers too.”
Ironically, the solution may lie not in new engines or stricter rules but in something simpler: maintenance. Poorly kept vehicles—regardless of fuel type—remain the biggest polluters. A targeted scrappage policy, regular inspections, and emissions enforcement may do more for India’s air than any fuel ban ever could.
In India, the story of diesel is not one of redemption but of reinvention. Faced with environmental crises, economic constraints, and evolving technologies, the industry has responded—not with denial, but with design. Clean diesel, if regulated wisely and applied judiciously, still has a role to play.
It won’t be a saviour. But it may yet be a survivor. And in the gritty, complex calculus of Indian mobility, that might just be enough.