The Diesel versus Petrol engine comparison has been ongoing since the time of their inception. Each has its pros and cons. The primary difference (as most of you already know), is that petrol engines use spark plugs to ignite the air-fuel mixture, while diesel engines rely on heavily compressed air without any spark plugs. So, in diesel engines, air is very heavily compressed, typically to around 14 to 23 times its original volume, while in petrol engines, the compression ratio is generally much lower (typically 7 to 10, with high performance compression ratios of up to 13).
For a driver, diesel and petrol cars deliver their oomph, in different ways. Petrol engines are all about revolutions per minute (rpm), and they tend to achieve peak power at higher rpm. As you upshift through the gearbox, you go faster – a sportier experience, if you will. Diesel engines deliver their oomph – in the form of torque that can push you up a steep hill – at lower rpm – very important when you are towing or carrying a load.
Diesel engines are more efficient and use 15−20% less fuel translating into cheaper running costs. Diesel cars with higher low end torque are excellent for cruising on highways, because overtaking is a breeze, often without even needing to downshift. However, they usually cost more than petrol vehicles as diesel technology is more expensive. Servicing or fixing a serious problem on a diesel car might be slightly more expensive in comparison to petrol cars. Diesels have lower CO2 emissions but pre-BS6 diesel vehicles produce tiny soot particles linked to breathing disorders such as asthma (not anymore). Diesel engines tend to be slightly noisier than their petrol cousins, but this has greatly changed with OEMs coming up with innovative solutions to manage noise. Modern diesels are so quiet that you can barely tell which engine you’re driving with the windows up.
Historically, diesels have tended to have a slightly higher resale value, but this is also changing with time. New diesel cars cost more by way of tax and depreciation is now slightly higher.
On the flip side then, Petrol vehicles are slightly cheaper to buy and service. They have higher CO2 emissions than diesel but produce less of some other emissions. They are quieter but also less efficient and use more fuel than diesels. Petrol engines do not produce as much torque as diesel engines and hence need to be in lower gear more regularly, for example when overtaking – but some drivers prefer this style of driving.
In the modern-day context, diesels and petrol engines are usually compared by way of their impact on the environment (emissions and noise). God knows we have enough of these environmental concerns. Air pollution, GHG emissions, management of waste, growing water scarcity, falling groundwater tables, water pollution, biodiversity loss, land and soil degradation, a reduction in the quality of life index, to name a few major environmental issues we face today.
I am sure that most of the readers of TOI would have heard of BS6. Bharat Stage-6 is an emission norm (government regulation) which codifies the emission thresholds which automobiles are allowed to emit during operation. India recently (April1, 2020 onwards) stepped up to the most stringent emission norm yet – BS6 (leapfrogging from BS4). The Indian auto industry has been busy getting ready and they have delivered.
BS6 is a stringent emission norm in itself but phases post BS6 are already in the planning phase. In post BS6 phases, auto companies will be required to design systems to monitor Real Drive Emissions (RDE). That is, a regulatory frame work to monitor your vehicle’s real emissions (on the road and not just certified in a lab). It will include a conformity factor to measure how much “dirtier” your vehicle exhales, as it is used and ages. Per the current roadmap, this regulation comes into effect after 2022.
Moving to BS6 is the right thing to do, considering the environment and associated health factors. Consumers are increasingly environmentally conscious and knowledgeable. They are more sensitive about an environment friendly products and accept “eco-friendly features” as USPs, (although, paying for the technology is another matter).
In addition to real environmental concerns, there are also perceived issues. There is a perception in some quarters that a few major cities may ban Diesel engines, or that the life of Diesel vehicles may be restricted in cities. This speculation brings into debate, resale value and you all know that cost and resale value are major factors in any car buying decision.
The Modern Diesel Engine
Diesel engines have always been more fuel efficient, durable and delivered more hauling power (torque) than gasolines. Typically, they contain less toxic pollutants but they did (in the past) have higher quantities of carbon (soot) in their exhaust than gasoline engines. Modern Diesel engines are incredibly advanced machines even compared to the ones from the early 2000s. Through incessant research in engine technology, OEMs and suppliers together have revolutionized them with innovations in engine design, exhaust emission control devices, the catalytic converter and ‘AdBlue®’, a chemical that helps reduce emissions. Modern Diesels are lighter than their predecessors, more efficient and far more technologically advanced. They are not the white smoke spewing diesels your grandpa might have owned.
How do they do it? The secret is a three-part recipe.
First – more efficient combustion by means of common rail high pressure diesel injection. This system improves fuel atomization, thereby improving ignition and the combustion process.
Second, by using more refined, ultra-low sulphur diesel fuel.
Thirdly, an advanced emissions control system which is the ‘brain’ of the machine and controls emission levels. This brain collects and processes signals and data from on-board sensors and then coordinates the Diesel Particulate Filter (or DPF), which reduces the emitted soot, and the Selective Catalytic Reduction (or SCR), which reduces Nitrogen Oxide (NOx), both, exhaust after-treatment systems.
There are several changes in the exhaust system of diesel vehicles making them more expensive than BS4 Diesels. BS6 compliant petrol vehicles are required to be 25 percent cleaner by reducing NOx (Nitrogen Oxide) numbers from 80mg/km to 60mg/km. For diesel cars, the BS6 norms aim at reducing three pollutants which include HC (Hydrocarbons) + NOx, PM (Particulate Matter) and NOx reduction by 43, 68 and 82 per cent respectively!
These facts notwithstanding, there is a widespread perception that diesel engines are bad for the environment, especially for Particulate Matter. It is true that particulates are bad for human health and contribute to smog and with a less than stellar emission record from recent history, the perception is natural. In the spirit of perception being reality, I have to accept the prevailing sentiment.
However, to anyone who’s listening, with BS6, the Particulate thresholds have been tightened for diesel from 25 mg/km to 4.5, which is the SAME as the limit for petrol engines. Did you know, that modern diesel engines convert up to 99% of combustion engine exhaust pollutants (HC, CO, NOx and particulates). The output is carbon-di-oxide, water vapor and inert nitrogen. Hence the new BS6 Diesels are equivalent for particulates to their gasoline cousins and they are more fuel efficient. As an industry we should make a concerted effort to communicate this fact to all stakeholders and to our customers.
But, changing minds takes time and with the pace things are changing (and the distracting din of electrification), I have a feeling that not too many people are in the mood to listen. Besides all that, what makes articulating this difficult, is the “price of entry” into BS6. With all the technical advances, DPF, SCR, Improved combustion, BS6 level Diesel engines are indeed costlier.
Beyond 2023 this will change depending on what Conformity factor will be decided by Indian regulations. If it is more stringent (<1.5) the Diesels will become even more expensive.
India is now part of the club of nations having the world’s cleanest petrol and diesel. The level of sulphur and nitrogen oxide content in fuel plays a significant role in emissions. Sulphur helps in lubrication inside the engine and combust the fuel more efficiently. BS6 fuel has lower sulphur content than BS4 fuel (five times lower (10ppm) in fact), so the new fuel uses additives that imitate the lubricating properties of Sulphur. At the same time, Nitrogen oxide level for the BS6 diesel engine and petrol engine were brought down by 68% and 25%!
Kudos to the oil Industry who met the BS6 timing challenge as well without either disruption or a price increase. Making the leap from BS4 grade fuel to BS6 just like the auto industry did. The change would have resulted in a cost increase but oil companies have not passed this on to consumers and instead adjusted it with the change in excise duty.
BS6 norms came in effect from 1st April 2020, and the BS6 fuel is (from what I can tell) dispensing across all petrol pumps in the country. Using BS6 fuel in BS4 or older cars should not result in any trouble. Using BS4 fuel may will result in higher tailpipe emissions in Heavy urban cycles. We should all expect a small amount of growing pains in smaller markets and this lockdown hasn’t made it easier.
So, as mentioned earlier, BS6 forces high tech advances on your engine. This technology comes at a price but no customer wants to pay for it. Why would they? It does nothing tangible for their everyday existence. They do love the environment but don’t ask most to put a price on this love.
From what I see, most companies seem to have introduced BS6 pricing at 20,000-30,000 more for petrol and 80,000-150,000 more for Diesel. Some OEMs have not passed on all the cost up for BS6 in their pricing (obviously taking a drop in margins which will affect the mix from the supply side. Why would anyone want to make and sell products which net them less to the bottom line with more effort). With de- regulation of Diesel prices, the gap between Diesel and Petrol Prices has reduced even before the BS6 introduction.
There will therefore be a shift towards Petrol vehicles in small and entry level midsize segments and this shift is inevitable.
The future of Diesel Engines in India
Sure enough, recent data suggests that there has indeed been a steady shift in customer preference towards petrol-powered vehicles (diesel mix has reduced in lower price segments over the past 2 years). I expect that this will continue for the smaller size vehicle segments. Maruti Suzuki’s announcement to discontinue Diesel engine (a good portion of their Sales volume) highlights this. Other manufacturers are also planning to discontinue smaller size Diesel engines. The increasing BS6 Diesel engine cost is an added accelerant to this end and like with everything, what will drive the mix change, is the magnitude of the price gap between diesel and petrol vehicles.
To most people, durability and improved fuel efficiency are intangibles (or intellectual derivations) but the increased price of the engine (on your sticker) and the increased price of BS6 fuel (at every gas station), is tangible. I expect the demand for petrol vehicles will likely increase as it has in Europe. The reason for the fall of Diesel demand in Europe, is it became more expensive for the customers, as OEMs increased prices to cover costs incurred in development and additional technical content because of ever tightening emission norms. Similarly, in India, there has been a reduction in the Diesel mix for small cars with the cost of meeting BS6 emission norms (these prices are further likely to go up with RDE because OEMs would have to adopt the SCR solution explained above).
The Way Beyond
Passenger vehicles which meet the BS4 and BS6 norms are very clean burning machines. Everyone reading this article should leave confident that your auto industry puts out products which are environmentally responsible. This is important because of the cacophony of contrary opinions which are not data based.
As I sit at home during this lockdown, I am beginning to sense that COVID might have added a dimension to this. Every day now, I see pictures of another city where Blue skies are suddenly the norm, where mountains ranges which were hidden are suddenly visible. Visibility which was measured in the hundreds of meters is now suddenly quoted in tens of kilometers. I submit that this is less because of passenger cars and other (stationary) sources of pollution are the bigger contributors.
Nevertheless, perception is that automobiles being off the roads has led to this improvement in visibility. As a reaction to this, if there are policy changes which accelerate plans to bring EV compliant networks before the target of 2030 and if the government starts focusing on infrastructure for electrical vehicles in near future, this could affect diesel vehicles enormously. Demand could start moving toward EVs and Hybrids. Hybrid (a much ignored powertrain) may be the immediate beneficiary (provided the tax code is changed) and EV quickly following after 4~5 years’ when India becomes self-sufficient in terms of charging stations, lithium waste management, etc. However, if you ask me there is probably one more BS norm we will get to see before EVs get here.
And what about diesels? Diesels will not go away in the near future. They will continue to have good market share in the larger and premium space because of their superior performance and fuel efficiency and because they meet the environmental norms at a better bang for the buck. Small displacement Diesel engines will see a larger drop, whereas larger displacement Diesel engines will remain in demand in the SUV segment which continues to show robust growth. This is because diesel-powered vehicles offer lower running costs and higher torque than their petrol-powered alternatives. In next 5 years, mid-size SUVs will continue to be Diesel dominated as they increasingly become lifestyle and recreation products, i.e. fueled by travel/ adventure/ experience. There are some on my team, who feel that it is even possible that people may own an SUV and share mobility, or public transport for daily commute.
Most Passenger cars have already dropped diesel from their line-up. So what’s next for Diesel, the complete answer is that this will depend on the cost of fuel, parts and maintenance, availability of BS6 support, fuel facility, government policies for electrical vehicles, etc. But that’s a complicated answer.
In my view, smaller passenger vehicles will have diminishing penetration of Diesel. The Compact SUV segment will have more or less same penetration of Diesel and Petrol engines. Larger PV segments will have higher penetration of Diesel with engines larger than 2-litre capacity. They will continue to dominate these segments with over 50% mix. In the premium segment, customers have reconciled to the reduced fuel price differential between Gas and Diesel and the Higher price for diesel-powered vehicles. As they slowly increase diesel vehicle price points the diesel mix may reduce.
Companies having premium SUV and sedans need to focus on pricing. In segment using diesel without SCR, diesel engines will continue to have more that 60% market share. However, with the SCR system (due to price it) will be reduced but will be still pushing 50%. Smaller and mid-segment petrol share will increase while Larger segments D and E SUVs will continue to be dominated by diesel engines.
Interested in a long-lasting, fuel-efficient, dependable powertrain for your vehicle? Check out a BS6 diesel-powered vehicle, you won’t be disappointed.
DISCLAIMER : Views expressed above are the author’s own.