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By, Vijai Christopher Sookrah, EIT, Mechanical Engineering Graduate Student, Combustion Research Laboratory, University of Toronto

In summer 2015, I was given the opportunity to complete a two month research exchange with the University of Castilla – La Mancha, in Ciudad Real, Spain, funded by BioFuelNet through their Highly Qualified Personnel (HQP) Exchange Grant. While in Spain I enjoyed the warm weather and sunshine while working with the Fuels and Engines group (Groupo de Combustiles y Motores, in Spanish) that has been studying the use of biofuels in diesel engines, biomass gasification, soot research, and related topics for over twenty years. During my time at the University, I worked on a research project regarding the optimization of diesel engines fuelled with various biofuels.

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Why study optimization of diesel engines fuelled with biofuels?

Well the answer is simple: we don’t currently certify or optimize engine operation when they are operated with biofuels. Weird, right? At least that is what I thought when I learned this.

Actually, some cars do optimize operation on biofuels, but these are only the “Flex Fuel” cars, which only represent a small, but growing percentage of in road vehicles in North America and Europe. Currently, most diesel engines are certified and optimized using pure diesel for North America, Europe, or where the engine (or car) is going to be used.

This means that engine manufacturers create engine operating procedures to minimize both the fuel consumption and greenhouse gas emissions (specifically oxides of nitrogen, NOx) at the same time; but only when the engine is fuelled with diesel. When a biofuel such as biodiesel (or blends) is used, the engine uses the exact same operating procedures as for regular diesel. This is problematic because the procedures were not developed and optimized for the biofuel actually running the engine. This results in less than optimal fuel efficiency and increased greenhouse gas emissions.

Biofuel mandates

Currently, Canada only mandates that 2% of the diesel fuel pumped from a gas station be of biofuel origin. Other countries, such as Argentina (10%), Brazil (5%), Costa Rica (20%), and Ecuador (10%) have much more stringent national mandates for biodiesel blending in the diesel pumped at gas stations. Furthermore, many states in the USA have varying incentives and some mandates for various percentages of biodiesel, with many gas stations offering 20% biodiesel blends. Additionally, European countries have mandates ranging from 2% to 10% biodiesel.

With that said, many of the regulations and mandates set by regional governments are set to change and increase the amount of biofuels in diesel over the next 5 to 10 years (see here for more info). Given that regulations and mandates for the percentage of biofuel required to be used in diesel are set to increase, engine certification will also soon see changes where biofuels are incorporated into the certification process. Therefore, getting a jump on the engine optimization when operating on biofuels would seemed like a good idea to the research group at the Fuels and Engines group at Castilla – La Mancha, in Spain.

Research project

As mentioned previously, engines are currently optimized to reduce both fuel consumption and NOx emissions at the same time. However, fuel consumption and NOx production are at odds. When one tries to minimize fuel consumption, NOx production increases. Furthermore, when one tries to minimize NOx production, fuel consumption is increased. This is what is known as the trade-off between fuel consumption and NOx emissions. This is also the reason why engines require complicated operating procedures written into the engine control unit (ECU), so that the engine is operating at the most optimal parameters that reduce both fuel consumption and NOx emissions at the same time.

The main parameters that affect the fuel consumption and NOx emissions are fuel injection timing (IT) and exhaust gas recirculation percentage (EGR). Therefore, to study engine optimization, IT and EGR were varied from the values determined by the ECU and both fuel consumption and emissions data were recorded. Fuel was injected earlier and later than the normal timing, while EGR percentage was increased and decreased from the normal value to study the effect that each change had on the emissions and fuel consumption. Very basic images are displayed below to illustrate the trends corresponding to variation of the parameters: injection timing and exhaust gas recirculation.

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Vijai3In order to study the effects of varying fuel injection timings and EGR percentage on the emissions and fuel consumption, we used one of the two engine test cells at the Fuels and Engines group; a diesel Nissan engine already instrumented and ready for engine trials. We tested 7 different engine power conditions to simulate the European driving cycle, varied injection timing ±2˚ from normal injection timing, and varied EGR ±10% from normal EGR. All this added up to 75 different engine test points for each biofuel tested; overall five different biofuels and blends tested. The engine was tested with: standard diesel fuel, 100% biodiesel, 36% biodiesel in diesel blend, 12.76% Ethanol in diesel blend, 20% Butanol in diesel blend, and a gas-to-liquid (GTL) fuel derived using Fischer-Tropsch’s (F-T) processes.

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When all the data was collected, it was analyzed and compared with diesel data and new optimization points were determined and related to the actual control parameters. For example, we are able to advise engine manufacturers, when running biodiesel in the engine, that starting injection earlier coupled with less EGR will produce better results for engine efficiency and emissions than using the normal operating procedures for diesel fuel.

The end goal of this project was to increase engine fuel conversion efficiency and reduce emissions when engines are operating on biofuels or blends. This is quite an important goal, because simply using a biofuel in your engine doesn’t really do any good if the engine isn’t working at the best operating conditions for that fuel.

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