Keeping Emissions In Check While Being Cost-Effective Is A Challenge

Written by  Anwesh Koley | 14 March 2017 | Published in March 2017 ( Interview )

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In recent times, auto major Mahindra has initiated a significant push in the areas of engine development and automotive design, which has helped the company enter new market segments. Entering new domains while strengthening its existing portfolio, the car maker has kept pace with the changing dynamics of an ever-evolving Indian automotive scenario. We met R Velusamy, Senior Vice President, Engineering and Component Development–Powertrain Division, Mahindra & Mahindra Limited, who shared his thoughts and insights on the engine development work being undertaken at Mahindra, and the way forward for the company in the years to come.

R Velusamy currently heads the powertrain division at M&M Ltd and is responsible for engineering and component development of multiple business verticals in the Mahindra group. He was also the head of the design, development and calibration team for the mHawk 2.2 l diesel engine, a state-of-the-art common-rail turbodiesel that currently powers the Mahindra Scorpio, XUV and Xylo. With four valves per cylinder, aluminium cylinder heads, variable geometry turbocharger and second-generation common-rail injection technology, this efficient and powerful unit has been a game changer for Mahindra. The world's first 2-cylinder CRDI engine, with four valves per cylinder, which was used to power the Maxximo compact commercial vehicle / minivan, was also developed under his leadership.

ATR_ How has diesel engine technology evolved over the years for Mahindra?

R Velusamy_ Mahindra started with the naturally-aspirated XDP 490 and the XD3P engines from PSA for its initial product line up. With the Scorpio, Mahindra entered the turbocharged diesel engine segment and over the years, advancements have kept pace with growing market demand. We had our share of challenges initially in terms of NVH, as the original IDI engines were known to have better NVH levels.

The advent of Common Rail Direct Injection (CRDI) technology provided the scope to upgrade the rate of injection as well as the pilot injection. Rate of injection refers to the quantity of heat released from the engine. When we introduced the pilot injection system, the rate of heat released was modified, thereby also muffling the noise. This is the single largest benefit of common-rail engines today. It helped in improving the fuel efficiency by around 4-5 % and also enhanced the availability of low-end torque. Common-rail direct injection helps in digitally modifying the injection timings and changing the injection sequence and mapping. It helps to have a more evenly distributed torque curve, which provides a better driving experience and improved fuel efficiency.

With emission norms getting stricter, how do you ensure your diesel engines meet all environmental requirements?

In today's fast growing automobile world, the emission limits are stringent; customer expectations of vehicle performance and fuel economy are more. Achieving these parameters for the given engine is a challenging task for any automobile engineer. BS IV emission limits are 50 % more stringent than BS III limits. With newer emission norms getting introduced, OEMs were initially struggling to achieve and adhere to the revised norms. This is because selection of appropriate technology for stringent emission norms has to be ensured in order to control higher costs and also to control adverse effect on fuel consumption.

The particulate emissions of diesel engines are different from their petrol counterparts, with nitrogen oxide (NOx) emissions being common for both. We have reached a stage where we do not work heavily on engines to ensure emission reduction. Only around 15-20 % of our research work goes into making our engines 'green.' The primary challenge lies in reducing emissions through after treatment. It is a new area and we are working to develop the after treatment process and making it reliable for the customer, while retaining the affordability of the vehicle.

European manufacturers initially introduced Diesel Particulate Filter (DPF) for diesel vehicles and this was followed by NOx reduction technologies. This was gradually implemented by carmakers across the globe, along with 'Lean NOx Trap' (LNT) being used for small capacity cars and selective catalytic reduction (SCR) for larger capacity cars. So today we have three elements in the equation: the engine, DPF and SCR/LNT, which can be worked upon to reduce emissions. All these technologies interact with each other to decide the best solution for a given situation.

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What is the post injection concept and how does it impact engine performance?

In the conventional diesel engine combustion process, the injection is targeted to hit the combustion bowl where it is expected to get combusted. In the late post injection concept, the diesel injector injects at a very retarded timing, thereby the hydro-carbons are released into the exhaust for increasing the exhaust temperatures via the diesel oxidation catalyst by an exothermic reaction.

As the injection impinges on the cylinder walls, the diesel dribbles through the piston rings and gets accumulated in the oil sump. This results in oil dilution, where the engine lube oil gets mixed with diesel fuel. With increase in the number of regenerations, the diesel level mixing with the lube oil increases, leading to diesel carry over into the intake pipe through the crankcase blow-by system. This results in unintended acceleration of the engine due to the fuel vapours. This phenomenon is called 'self-acceleration.'

The increased number of regenerations will result in increased oil dilution with diesel. With increasing traffic, the regeneration duration is increased and subsequently there's more oil dilution. In real world driving conditions, with average oil change interval of 15,000 km and considering 60 regenerations, oil dilution is expected to be around 7 %. Oil dilution results in self-acceleration of the engine and causes significant engine damage due to deterioration of oil lubrication properties.

Ash accumulation is another challenge, which reduces engine life and performance. Ash gets deposited in DPF as a result of burning oil-borne soot and fuel-borne sulphur. This results in increased back pressure and reduced volume for soot storage. The expected lifetime of DPF also depends on the ash storage capacity of the DPF. A DPF functions like an air filter. When we put an air filter inside the intake manifold, we can avoid dust from entering the engine.

What are your thoughts on the need for CO2 reduction and engine downsizing?

CO2 reduction occurs at multiple levels and areas. For the engine, it is important to reduction friction during its normal course of operation. This is applicable for both cold friction during rapid warm up and warmed-up friction. It is also important to ensure the right engine size for a particular vehicle, given its weight and expected driving conditions. Reducing cubic capacity and increasing power density can help achieve this end. Weight reduction through modular parts design and efficient plastification of parts are methods widely being adopted globally, to reduce vehicle mass.

Downsizing an engine is done to increase efficiency. Engine combustion is a thermodynamic process and a certain amount of heat is used up by exhaust, in the engine cooling process and due to internal friction. In the energy conversion process, 45 % heat is lost, so only 55 % can be converted into usable energy. When this 55 % energy is converted at the point of conversion, an additional 10 % is lost in friction in running the pistons, the crankshaft, the connecting rods, the valve train and many other processes. In a downsizing process, we have incomplete burning combustion facing heat through walls. This means that when we reach lower temperatures, the heat released through the walls is very high, as the engine is cold. A lot of heat is lost through the walls and the heat transfer from the piston does not take place. However, if a car runs cold during city driving, all the metal parts within the engine manifold stops receiving heat. This can be avoided through downsizing, as it helps avoid running on lower loads. Also, with additional safety equipment adding weight to a car, manufacturers today resort to using turbochargers to extract more power from the existing cubic capacity of an engine.

Most of the engines in the market today are naturally aspirated. The first step is to downsize the engines and add a turbocharger. The next step is to have port induction and direct injection. Further, manufacturers can have a Miller cycle during the gas exchange process. All these four technologies combined can result in a gain of about 13 % energy.

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What was most significant about the mFalcon petrol engine's development?

The mFalcon engine currently being used in the KUV 100 has been developed from scratch in-house. We were clear that we need a naturally-aspirated 3-cylinder, 1.2 l engine, which should not exceed 1,000 kg in weight. We decided to have a 3-cylinder engine, as most of the cars in this segment had a similar configuration. The power and torque figures were finalised to keep the KUV 100 at par with the competition. We have used plastic manifolds, four valves per cylinder and variable oil pump and for the first time we have introduced an over-running clutch mechanism. Dual VVT (variable valve timing) has been used along with a silent chain for smoother operations. All our engine development efforts are directed towards achieving higher fuel economy levels and create a benchmark in the segment.

The decision to have a 3-cylinder engine was to keep costs low, and the increase in the bore and stroke dimensions through an added cylinder will not bring a dramatic change in performance. When we increase the engine length through the additional of an extra cylinder, we double its weight, but if we increase the height of an engine structure, only half the weight goes up. Also, with the addition of an extra cylinder, engine mass goes up, but the increase in power output is not in proportion to this weight rise due to increased friction. A three-cylinder engine inherently has lower NVH levels as well, which is a major criterion for engine development today.

What are Mahindra's future plans in terms of engine development, especially in the context of exploring foreign markets?

The European market has around 52 % diesel cars and 48 % petrol vehicles, while the Chinese market has 98 % cars running on petrol. In the Indian scenario, 35 % vehicles are diesel and the remaining 65 % run on petrol. This is primarily due to the SUV market being smaller than the hatchback and sedan market, with the latter being largely petrol-driven. However, with the new-age entry-level SUVs coming into the market, the equation is changing and customers are finding more value in a diesel engine.

The introduction of BS VI will also have an impact on the way customers perceive diesel engines. As manufacturers, we have to monitor the change in cost dynamics and how the final product will shape up. Also, there will be additional safety requirements, which will be mandatory by 2020, thereby adding weight to a vehicle. Our course of action will depend on how much petrol technology will advance in these interim years and how can we being diesel costs down. The fact that we have been successful in selling more petrol units of the KUV 100 than the diesel variant is a sign for things to come from Mahindra in the future.

TEXT: Anwesh Koley

PHOTO: Mahindra & Mahindra Ltd

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