Turbocharging 10002
Apr 16 2016
Aman Kumar

Turbocharging a FSAE car is a goal for every other team, to gain improved engine performance, which, in the case of FSAE is limited due to the 20mm air intake restrictor for petrol cars. So, our team also took this up as a challenge for improving the current powertrain design. We decided to turbocharge a 373cc KTM Duke390 engine, replacing our old worn out 600cc Honda CBR engine.

So our team began reading up theory and calculating boost pressure values for different turbochargers available in the market.

One fine afternoon in the August of 2015, I saw the notification of a technical essay writing competition organised by ABB Turbo systems ltd, Switzerland as part of the celebrations for the 110th anniversary of the invention of the turbocharger invention. It was on 16th November 1905 that Dr. Alfred Büchi received his patent for the design of the Turbocharger. I decided to take part and utilise the knowledge i gained till now on this topic.

My essay was ranked among the international top 10 entries by a panel of expert engineers from ABB qualifying for a consolation prize of a GoPro Hero. My entry was the only winner from India, and top 3 were 24 year old PhD students from Europe. It gave me great satisfaction to stand on the same pedestal as these passionate automobile scholars, when I’m 21 and doing my B.Tech in Mechanical engineering. Read more

I've attached my essay, for the automobile enthusiasts among you. Hope you enjoy reading it.

I stayed back in campus during the winter of 2015 to complete designing work. After reading many research papers and blogs, and long calculations, I was able to get a good boost ratio. I then ran simulations with help of other team members using Ricardo WAVE to verify the brake output produced. Our calculations and engine model seemed to work correctly. So we showed this to a product engineer from Honeywell, who was impressed with our design work and offered to sponsor a cute little boosting hardware unit.

Cheers to Abhimanyu Das, who has been working overtime throughout this year to make this happen. I hope, he will be able to practically implement on our next FSAE car with other team members. Best wishes to all of you and good luck with your new car. Stay tuned for more and feel free to mail/ping me or comment below for any query.

110 years of turbocharging

After the invention of the 4 stroke IC engine in 1876 by Nicolas Otto, people discovered that the naturally aspirated engine's maximum power delivered was limited by the amount of fuel that can be burned efficiently, which depends on amount of air entering into each cylinder per cycle. So, total mass of air inducted per cycle decides different output characteristics of engine such as power, torque and MEP (mean effective pressure). Hence the idea of forced induction appeared promising to overcome this limitation. Many techniques for forced induction has been invented since then, in late 19th and early 20th centuries, such as Supercharging, Turbocharging, and Pressure wave supercharging.

Applications of supercharger is constrained, as it needs to be mechanically driven by the engine or external electric motor. So some power needs to be drawn from the engine to drive the supercharger. Also it has lower adiabatic efficiency compared to turbocharger. On the other hand, turbochargers use hot working fluid (exhaust gas) to drive a turbine and a mechanically coupled compressor to generate power boost. These factors led more application of turbocharger in engines as compared to other boosting methods. Turbochargers can be used for boosting two stroke and four stroke diesel and gas engines.

So this technology finds wide spectrum applications in automotive, aeronautical, marine, industrial, rail and oil drilling industries. In two stroke engines, turbocharger raises boost pressure at inlet port above the exhaust pressure for better cylinder scavenging and also provide additional power density. In four stroke engine, it increases the power per unit displaced volume and lowers down BSFC (brake specific fuel consumption) giving better fuel economy. Different engines have different applications and different power output requirements, so new challenges need to be addressed leading to technological improvements. Turbines operate more efficiently under steady flow conditions, but exhaust manifold produces unsteady flow making it less efficient. So, radial flow turbines are normally used in automobiles, and axial flow turbines are used for larger engines such as locomotives and ships. Turbocharged spark ignition engines have lower compression ratio than naturally aspirated engines, because charge self-detonates for same octane rating of fuel. So, air is cooled via an Intercooler, rich mixture is used and spark is retarded at WOT (wide open throttle) at high engine speed to further increase volumetric efficiency and prevent charge from self-detonating or knocking. A flow control valve or Wastegate is installed before the turbine to bypass exhaust gas and control boost pressure by increasing orifice diameter at high engine speed. This avoids fuel penalty due to rich mixture and decrease of BMEP (Brake Mean Effective Pressure) at spark retardation.

However, the challenge of turbocharging a diesel engine is totally different as compared to gasoline engine. Higher compression ratio would develop more stress on critical components such as Journal bearings, and hence we would need to limit maximum cylinder pressure. Also, achieving smoke emission standards, limiting harmful emissions such as CO, SOx and NOx generated by a diesel engine, at 0.7 to 0.8 equivalence ratio (Air-fuel ratio). Direct Injection of fuel into combustion chamber helps to meet these shortcomings.

Higher BMEP can be obtained with two-stage turbocharged after-cooled diesel engines. More oxygen leads to better mixing and charge combustion, so NOx emission is also reduced by a significant value, and also BSFC decreases, which means lower fuel consumption at target power output. For getting ball-park estimate of impact of these advantages, we can take the example of Maersk Triple E class container ship, which can transport 115.5 million pairs of sneakers in a single trip from US to Europe.

Travelling about 8000 kilometres at 14 knots speed, it would take 2 weeks time to reach its destination, and will consume around 380 tons fuel per day. So total cost of bunker fuel ($282/ metric tonnes) would be roughly $1.5 million. If this engine wouldn’t been turbocharged, fuel consumption would rise by 20% to maintain same ship speed at higher engine load, consuming around 456 tonnes fuel per day, thus increasing fuel purchasing cost to $1.8 million. And, 70% of all operating cost is fuel. This would increase ship’s own weight and reduce goods carrying capacity further, and sneaker cost would rise nearly by $1 per pair.

Globally, transportation industry is undergoing a transformation due to changing consumer preference towards vehicles with a lower carbon footprint. Governments are adopting and implementing stricter laws for lower emissions and high fuel economy such as EURO 5 and EURO 6 by 2020. So, OEMs are focusing on the most cost-effective technologies capable of being deployed on mass-produced models. Turbocharging provides flexible solution to major restrictions and leading to industry wide downsizing of engine. Downsized turbo engines can be 20-40% more fuel efficient in diesel and gas engines at same maximum power and part load. New solutions implemented are two-stage turbocharger, Wastegate control management and variable turbine geometry. Dual fuel technology and Water Injection system on turbocharged engines are showing further scope of improvement in terms of emissions, efficiency and power. Recently, BMW implemented innovative water injection technology in its M4 Sports model to generate power boost at high engine RPM.

When water is injected in optimum ratio to fuel into cylinder, it gets converted into steam at higher temperature, creates extra in-cylinder pressure, absorbs harmful CO and NOx, lowers operating temperature of engine and exhaust emissions by absorbing heat produced. Automotive giants will soon implement this water injection in GTDI engines for passenger cars too. Also, Ricardo, a global engineering, strategic and environmental consultancy has updated its engines simulation software, WAVE 2015 version, where its global customers can simulate engine models with multi-fuel combustion and water injection and observe performance benefits. Overall, we can see positive and growing market for turbocharging in various industries in the coming years.

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