This paper reports results of an experimental investigation performed on a commercial diesel engine supplied with fuel blends having low cetane number to attain a simultaneous reduction in NOx and smoke emissions. Blends of 20% and 40% of n-butanol in conventional diesel fuel have been tested, comparing engine performance and emissions to diesel ones. Taking advantage of the fuel blend higher resistance to auto ignition, it was possible to extend the range in which a premixed combustion is achieved. This allowed to match the goal of a significant reduction in emissions without important penalties in fuel consumption.
The experimental activity was carried on a turbocharged, water cooled, 4 cylinder common rail DI diesel engine. The engine equipment included an exhaust gas recirculation system controlled by an external driver, a piezo-quartz pressure transducer to detect the in-cylinder pressure signal and a current probe to acquire the energizing current to the injector. Two operating conditions were tested, 2000rpm@0.5MPa of BMEP and 2500rpm@0.8MPa of BMEP. The effect of injection pressure, start of injection and exhaust gas recirculation for these different combustion regimes were explored in order to understand how they affect the combustion process and engine out emissions.
Retarded SOIs joint to reduced O2 concentration at intake allowed to increase the ignition delay providing more time for the air-fuel mixing before auto-ignition. As a result, a partial premixed combustion was achieved for both fuel blends with an improvement in smoke and NOx emissions.
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