‘We have begun developing a series of new diesel engines for a European OEM for off-road applications.’

Neelkanth V Marathe, Senior Deputy Director & Head (Powertrain Engineering), The Automotive Research Association of India (ARAI), a veteran with over three decades of experience in engine and transmission R&D at ARAI, speaks to Amit Panday about the future of diesel engines, complexities involved in balancing emission reduction with fuel efficiency, an ARAI-developed all-new diesel-CNG dual fuel engine and an exclusive contract from a European OEM. Excerpts:

There is a lot of pressure for developing cleaner technologies within which combustion is one major area of concern. Can you tell us about recent developments at ARAI within the powertrain division?
Certainly as we found out from various presentations and sources, we need to reduce the emissions from the engines, and there are no doubts about that. This is being done in steps. First of all, the big question is how we can make the engine as clean as possible without bringing much penalty to the fuel economy.

Normally, any work we do in reducing the fuel emissions has a trade-off, which is the fuel consumption. Advanced technologies that are there in front of us such as the high pressure injection system, different types of combustion concepts and the various things can be done with the overall mechanical design of the engines (reducing the weight of moving parts, reducing friction and many other areas) so that the overall fuel consumption can also be reduced while they are working on the reducing emissions.

Speaking about a diesel engine, it emits NOX, particulate matter and smoke – these are the three areas of concern. Out of these, smoke is the visible part. Any amateur can look at the smoke emitting out of the exhaust and comment that it’s a bad engine. A lot can be done in the areas of reducing the emissions of NOX, particulate matters and smoke.

Diesel engine technology has a very bright future in terms of reducing emissions to almost near-zero. But the technologies involved are costly. There is a technology available; it can compete with other fuels, and the kind of performance that the diesel engines are attributed to, there are no parallel technologies to that. Fuel economy is usually is better with diesels because of the kind of combustion process that happens. However, the CO2 emissions are also high. What I would like to say that diesel has a good future and we should not outrightly say that diesel is dirty.

What is the low temperature combustion (LTC) concept?
The concept of low temperature combustion (LTC) is being discussed in many events but it is not commercially available. This concept has a possibility wherein NOX and particulate matter both can be reduced, and it also gives the benefit of good fuel economy. This is the superiority of this concept.

When we do this LTC type of combustion development it, at present, covers a very narrow band of engine. Now to widen this so that it covers most of the points of the engine, you need to bring some higher end technologies, flexibility in the engine operations. For example, we are trying to find out the impact of variable valve timing, variable valve lift, variable fuel control, variable compression ratio and others. It is a combustion concept to bring more load points of operation of the engine under the regime of combustion control and emission control. We are seeing a lot of turbocharging applications.

We are also trying to find out the ways and means if mechanical supercharging will work in addition to turbocharging. All these developments are associated with the trend of engine downsizing. We are heading towards smaller engines as they work more efficiently, so the emissions will further reduce. But that will put more burden on turbocharging.

Is engine downsizing not at all possible without turbocharging?
Yes, because you want to get more power from a small engine. In this case you have to put efforts into putting more air into the engine to burn more fuel. And unless you burn more fuel, no more power can be developed. So we need to have turbocharging.

If it goes beyond a certain point, then there is a requirement of making the turbocharging in two stages. The two-stage turbocharging comes with a different packaging, costs, complex exhaust system, hot engine operations and other factors. I believe that a combination of exhaust turbocharging and mechanical supercharging may be a good solution and in this case we may not be required to increase the stress on the exhaust systems.

With increasing loads coming on the engine (thermal load, mechanical load, dynamic load), the thermal management of the engine is becoming very tricky. Unless we make sure that the thermal management is under control (via cooling, lubrication), we will not be able to add reliability and durability to the same. So putting all these factors together, there is a future where the diesel engines can meet near- zero emission levels in competition to other fuels, and at the same time, its life can be made longer and the benefits of the engine performance can still be available to the society.

Further, if you think about adding hybridisation to the diesel engine that will only add to its benefits.

But is the deployment of turbocharging, which is usually associated with generation of high temperatures in the engine compartment, and the low temperature combustion concept contradictory to each other in terms of the common criteria of achieving efficiency through safer means?
Not necessarily. Turbocharging is used to get more air inside the combustion chamber so that we can burn more fuel. Yes, the temperatures do go up rapidly in this case but that can be controlled by intercooling. While on one hand we want to get more air inside, turbocharging does that job, it increases the temperature of air, we lose density and mass, and to recover that we use intercooling or after-cooling. So ultimately it will be a package of engine downsizing with turbocharging and intercooling or with two-stage turbocharging with may be another turbocharger or a mechanical supercharger.

The problem comes with the concept that diesel engines have higher compression ratios, which means higher temperatures and therefore more emission of NOX. High temperature, on the other hand, is required for good combustion, which will reduce the particulate matter and the smoke. That is a trade-off.

Now we want to find out a possibility where the engine burns at a lower temperature so that NOX emissions can be controlled and support the same with advanced technologies such as high pressure injection systems so that the emission of particulate matter and smoke are also kept under control. So this is a concept that is not at all easy. This is extremely challenging and involves tremendous work that we have taken up at ARAI. May be it will take another two-three years from now when we will have some breakthrough. This work is also going on in Germany and other countries in Europe.

So no breakthrough has ever happened in this technology so far?
The concept is working but it is not commercially introduced so far. So we are all working towards widening the applications of this concept, bringing down the development costs is another area. To widen its applications, we have to work on the variables in the engine operations such as variable valve timing, variable valve lift and others – one of these or a combination of all. I won’t be able to comment on when, how and at what costs all this can be done.

ARAI has developed a diesel-CNG dual fuel engine. Can you tell us something about that.
Yes, we have developed a diesel-CNG dual fuel engine for SUV and bus applications. It has got very good results. Now we are working on some off-road engines also.

What is the configuration of this diesel-CNG engine?
The beauty of a diesel-CNG dual fuel engine is that it is a diesel engine. There is no change of converting the diesel engine into a spark ignition engine. So it remains as the diesel engine and the diesel fuel works like the primary fuel.  It is displaced by the CNG in different percentage and in different speed-load conditions. So mostly we would try to work with CNG replacing the diesel as much as possible. Within the gamut of work that we have done at ARAI, we could find that maximum replacement was around 70-75 percent in a particular speed-load combination, and the average replacement (of diesel fuel by CNG) was about 40-43 percent.

The other real benefit of this engine model is that whenever there is no CNG, you can switch over to the diesel fuel mode and it will work without any redundancies. In such a scenario, it will work as a perfect diesel engine, meeting all emission norms. The biggest issue with a dedicated CNG engine, as we all know, is that it may not be able to go beyond the boundaries where CNG is not available.

Are these prototypes built on 2.5-litre or 3-litre diesel engines? What is the current status of this new dual fuel engine platform?
Yes, so we have worked on 2.8-litre and 3-litre engine platforms used for bus applications. This dual fuel engine will have a bright future. We are trying to find out how this can be allowed to be commercially used. We are discussing this across many forums. Even the government is discussing about passing a notification where dual fuel can be allowed in transportation.

ARAI has also developed a three-cylinder diesel engine from scratch. Can you share with us the updates on that?
This was quite some time ago. This was a three-cylinder, downsizing project. The work done was quite satisfactory. This is a 1.5-litre, 3-cylinder engine that is designed to deliver a peak power output of close to 150hp (112kw). Our first prototype, which we have developed and is running in our engine dynamometer, is developing 100hp. However, this engine is designed to deliver up to 150hp. We are demonstrating this as Indian engine design technology and those who wish to buy it from us, we will sell it to them with proper design transfer. The engine, which was developed at ARAI ground up, is now ready. It took us 3-4 years to us to design and develop this powertrain.

ARAI is working on multiple diesel engine platforms for European vehicle manufacturers. Can you throw some light on the same? Is this an exclusive contract to ARAI?
Yes, we are thankful to our clients who trust us and our capabilities. We did work for a Chinese OEM wherein we had developed a completely new engine for them. Based on the success of that engine, which was implemented commercially in several parts of the world by them (they are producing it), they have given us a project of developing another new engine for them.

Recently, we have started developing a series of new diesel engines (including three-cylinder, four-cylinder) of certain power range, which I won’t be able to disclose at this moment, for a European OEM for off-road applications. This would be another very important project for us where we will be developing completely new engines from scratch. These engines would be capable of meeting higher level of emission norms so that in future the basic mechanical engine design remains unchanged. We have reached halfway under this project, and may be in another few months, the prototypes will be ready.