However few studies have examined the impact of biodiesel use on the AS

However few studies have examined the impact of

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However few studies have examined the impact of biodiesel use on the AS behavior and only in the last decade some attention has been given to the analysis of DPF performance during loading, passive regeneration and active regeneration processes. With respect to this point, in this paper an experimental study of a non- road Diesel engine coupled to a DOC-DPF system is proposed to analyze several effects of biodiesel blending on the operation of the AS, in terms of PM-NOX engine-out trade off, NO-NO2 conversion efficiency of the DOC and soot reactivity. 2. Experimental Setup Engine tests were performed at the engine test bench of the University of Rome “Tor Vergata” on a non-road 4.0 liter diesel engine DEUTZ “TCD 2012 L4”. The exhaust AS includes a DOC and a DPF. Two different blends, B06 and B30, have been studied by blending fossil fuel and Waste Cooking Oil biodiesel. Further details on fuel specifications and the emission measurement instruments rig configuration for emissions monitoring can be found in [4]. 2.1. Engine test matrix Steady-state engine emissions and AS behavior over a 3-4 h transient period were evaluated during the repetition of the six engine modes described in [4]. The baseline engine calibration has been hold in order to analyze its different response to attain the defined mode by varying blend. The DOC steady state conversion efficiency was evaluated performing a repetition of engine modes in order to have an increasing inlet DOC temperature.
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3. Results and discussion 3.1. Engine performances and emissions The biodiesel lower heating value (-3.9%) gives an average increase of 2.8% in brake specific fuel consumption (BSFC) of B30 with respect to B06. On the other side, the lower B30 stoichiometric air-fuel ratio compensates for its lower air/fuel ratio and thus the equivalence ratio is slightly higher (+1.1%). An increased injection pressure and duration, in order to compensate for biodiesel lower heating value [3], can be considered the reasons for the slight increase of NOx emissions (+2.6%) as reported in [4]. The significant reduction of PM emissions (-6.8%) is primarily due to the higher oxygen content of the B30 blend, as it is proved by the increased emission reduction at high engine load [4], where the combustion is mostly diffusive and local rich zones are more present [5, 6]. Furtherly, no solid conclusions can be drawn about CO emissions (particularly at low load conditions) while a limited increase in CO2 emissions (+1%) is a result of the lower air-fuel ratio [7]. 3.2. DOC conversion efficiency In order to analyze the contribution of NO-NO2 conversion efficiency on DPF operation, both steadystate and transient analyses have been carried out. The steady-state NO2/NOx ratio shown in Figure 1 highlights a similar trend upstream of the DOC. The analysis of the downstream ratio gives two main indications: Below 190°C the NO-NO2 conversion efficiency is negative for both the blends, probably due to NO2 reduction by HC [8] Between 255 and 380°C the B30 has a slightly higher efficiency. This
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  • Spring '13
  • DAVIS

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