Research Overview

My research is on a novel method forturbocharging single-cylinder four-stroke internal combustion engines to create a cleaner, more compact, fuel efficient and lower cost power source for small-scale farmers in India. Turbocharging uses energy from an engine’s exhaust to compress the intake air, this allows the engine to combust more fuel. Due to the pulsating nature of flow this technology is not currently used in single cylinder engines. I have built a new style of manifold that buffers the air flow. So far I have validated this method through both experiments and computational models.

This Video is a quick overview of my research. It was made for the Lemelson MIT student prize competition.

Motivation

The goal of my research is to create a more powerful, lighter, more fuel efficient, and lower cost single cylinder four-stroke internal combustion engine. These improvements were achieved by turbocharging. A turbocharged engine has better fuel economy, cost efficiency, and power density than an equivalently sized, naturally aspirated engine. Most multi-cylinder diesel engines are turbocharged for these reasons. However, due to the timing mismatch between the exhaust stroke, when the turbocharger is powered, and the intake stroke, when the engine intakes air, turbocharging is not used in commercial single cylinder engines. Single cylinder engines are ubiquitous in developing world off grid power applications such as tractors, small vehicles, generators, and water pumps due to their low cost. Turbocharging these engines could give users a lower cost and more fuel-efficient engine. The proposed solution is to add an air capacitor, in the form of a large volume intake manifold, in between the turbocharger compressor and the engine intake to smooth out the flow.


Theory

The amount of air that the engine can intake limits the amount of fuel that the engine can burn. This in turn limits to the amount of power an engine can produce. If an engine can intake more air, it can burn more fuel and produce more power. Currently, commercially available single cylinder engines are naturally aspirated. A naturally aspirated engine intakes air directly from the atmosphere. This limits the amount of air it can intake and thus its peak power. A turbocharger compresses the intake air and thus increases its pressure and, as a result, the intake air density rises. This allows the engine to burn more fuel per cycle, which increases the power output of the engine. A turbocharger consists of two parts, a turbine and a compressor. The turbine is connected to the exhaust stream of the engine. It uses the energy from the high pressure and temperature exhaust stream to power a compressor. The compressor pressurizes the atmospheric intake air, increasing its density. The engine intakes this higher density air and, as a result, can burn more fuel. Through this process, a turbocharged engine can produce more power than a naturally aspirated engine.

There are two reasons why turbocharging leads to fewer losses and increased fuel economy. First, turbocharging a smaller engine gives the same power output as a larger engine, allowing for fewer frictional losses. This is because a smaller engine has less frictional area between the piston and the cylinder. Second, due to larger mass flow rates of air, there is better heat transfer in the engine, which reduces cooling losses. A study done on several hundred passenger cars found that turbocharging commercial vehicles resulted in a 8-10% boost in fuel economy, a 30% reduction in engine size, and the potential to provide an even higher 18% fuel economy boost.

Turbochargers increase the power density of engines by increasing the amount of power provided by the cylinder per cycle, which is crucial for weight sensitive applications, such as aircraft, and equipment that needs to be moved using human power, such as water pumps. Turbocharging has also been shown to reduce emissions. Studies have shown that increasing the intake pressure also reduces nitrogen oxide emissions and that turbocharging can reduce carbon dioxide emissions in diesel engines by 30-50%.

In a single cylinder engine there is a phase difference between the intake and exhaust stroke. This means when the engine is exhausting (when the turbocharger is powered) the engine is not intaking, and the compressed air has nowhere to go. Due to the varying nature of single cylinder exhaust pulses and the phase mismatch, commercial single cylinder engines are not currently turbocharged, despite the advantages. The proposed method of turbocharging single cylinder engines is to add a volume to the intake manifold, referred to as an air capacitor. The air capacitor acts as a buffer to store compressed air between intake strokes and smoothes out the peaky nature of a turbocharger, operating under pulsating inlet conditions.

The size and shape of the air capacitor are critical to its performance. A volume that is too large will cause excess turbo lag due to the pressurization time of the capacitor. A volume that is too small will cause a large pressure drop in the intake manifold pressure during the intake stroke, negating the benefits of the turbocharger. The shape of the intake manifold is important to minimize pipe losses and resonances in the system.


Results

This research has yielded significant amounts of new computational, analytical and experimental results that can be accessed through reading one of the three peer reviewed papers and the master’s thesis linked bellow (also listed in the publication section)

Investigating the Effect of Intake Manifold Size on the Transient Response of Single Cylinder Turbocharged Engines [🔗]
Buchman, M., & Winter, A.,13th International Conference on Engines and Vehicles (2017)

Validating a method for turbocharging single cylinder fourstroke engines [🔗]
Buchman, M., & Winter, A., 18th International Conference on Advanced Vehicle Technologies ASME IDETC/CIE (2016)

Method for Turbocharging Single Cylinder Four Stroke Engines [🔗 ]
Buchman, M., & Winter, A., ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference (2014)

A methodology for turbocharging single cylinder four stroke internal combustion engines [🔗 ]
Buchman, M., Master's Thesis (MIT, 2015)