Session: 02-02: Alternative CI Fuels, Ignition, and Combustion Strategy

Paper Number: 197306

197306 - A Systematic Characterization of N-Butanol-Diesel Blends to Neutralize the Nox-Soot Tradeoff in Heavy-Duty Diesel Engines 

Abstract: 

Heavy-duty diesel engines have traditionally faced the well-known, intransigent tradeoff between engine-out emissions of oxides of nitrogen (NOx) and soot.  When considering liquid alternative fuels for diesel, new opportunities arise for devising strategies to neutralize the NOx-soot tradeoff.  In the present work, the authors studied neat n-butanol and an n-butanol-diesel blend (80%-20% v/v), termed "80B20D" for short, over a wide range of loads (IMEPg from 5 bar to 15 bar) at 1339 rpm (“B speed”) on a single-cylinder, heavy-duty, direct-injection diesel engine.  N-butanol was chosen as the liquid alternative fuel to diesel because it facilitates a stable blend with splash blending and also has very good lubricity (significantly better than standard diesel) such that it can be used as a standalone fuel or blended with diesel using existing fuel injection systems without any special additives.  It was hypothesized that the higher autoignition resistance of n-butanol (compared to diesel) could result in longer ignition delays, facilitating better mixing and potentially longer spray liftoff lengths, which when combined with the fuel-bound oxygen in n-butanol could lead to lower soot emissions.  Detailed results were obtained for combustion pressure and apparent heat release rates (AHRR), engine performance, and exhaust emissions for a variety of parametric variations, including start of injection (SOI) of the fuel, boost pressure, multiple injections, and exhaust gas recirculation (EGR), among others.  Compared to conventional diesel combustion on the same engine, the 80B20D blend exhibited “virtually zero” engine-out smoke emissions (measured as filter smoke number or FSN) at all operating conditions.  To mitigate NOx emissions, SOI retard, pilot injection, and EGR were studied.  In all instances, engine-out NOx emissions were reduced with no impact on engine-out smoke (FSN) emissions, thus neutralizing the NOx-soot tradeoff.  However, with pilot injection alone, engine-out carbon monoxide emissions were higher.  Gross indicated fuel conversion efficiencies with 80B20D were similar to or slightly lower than conventional diesel operation, but high maximum pressure rise rates were evident at the lower load of 5 bar IMEP compared to diesel.  Overall, n-butanol appears to be a promising drop-in liquid alternative fuel for conventional diesel fuel in heavy-duty diesel engines with more manageable challenges compared to other fuels.

Presenting Author: Yamini Baskara Babu The University of Alabama

Presenting Author Biography: Yamini Baskara Babu is a Ph.D. Candidate in the Department of Mechanical Engineering at The University of Alabama. Her doctoral research is focused on characterizing alcohol fuels for modern heavy-duty compression ignition engines.

Authors:

Yamini Baskara Babu The University of Alabama
Hariraja Thothadri The University of Alabama
Anurag Gaur The University of Alabama
Sundar Rajan Krishnan The University of Alabama
Kalyan Kumar Srinivasan The University of Alabama