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All the experimental investigations performed in the last years on newly sold motorcycles, equipped with a three-way catalyst and electronic mixture control, clearly indicate that CO and HC cold additional emissions, if compared with those exhausted in hot conditions, represent an important proportion of total emissions. Consequently, calculation programs for estimating emissions from road transports for air quality modeling in dedicated local areas should take into consideration this effect. From this motivation, an experimental activity on motorcycles cold emissive behavior is being jointly conducted by Istituto Motori of the National Research Council (IM-CNR) and the Department of Mechanic and Energetic (DiME) of the University of Naples.

The exhaust emissions produced by the combustion of methyl ester of rapeseed oil (biofuel) have been compared with the ones obtained using a commercial diesel fuel. The tests have been carried out on a Direct Injection Turbocharged (DITC) diesel engine according respectively to the ECE 15, to a non standard STOP and GO test cycle and to the European 13 MODE test procedure. Similar engines running at the same injection timing have been adopted in performing the transient and the steady tests. PAH emissions have been measured on transient cycles. The effects of injection timing and of Exhaust Gas Recirculation (EGR) on the emission in steady state tests has been evaluated too. In particular an exhaust oxydating catalyst has been employed in presence of EGR. The tests carried out indicate that, at the same injection timing, methyl ester promotes a rise in NOx emission, a decrease in HC and CO as well as a strong reduction of smoke.

Regulated and some unregulated emissions of a medium size non catalyst vehicle obtained with different formulations of unleaded fuels have been measured. Among the unregulated pollutants, 1-3 butadiene, benzene, toluene and polycyclic aromatic hydrocarbons (PAH) have been considered because of their toxicological hazards [ 1 ]. The emission levels have been compared with the ones obtained in similar conditions using a leaded reference fuel. Cold start Europe cycle and two not standard cycles have been used as basis of comparison for pollutants measurements. The effect of a three way catalytic system, fitted on the same vehicle, on regulated and unregulated emissions has been also studied, evaluating the conversion efficiency for the different pollutants. The same fuels have been tested in the same driving conditions on a small size passenger car too, equipped by the factory with catalyst and closed loop control system.

A reason of the lack of agreement between measured pollutants concentration in the air of urban areas and vehicle pollutant emissions evaluated by available emission models is the fact that catalyst performance variability is not considered. In this paper, an experimental study on the effect of performance variability of catalyst on emissions is presented. Average emissions have been measured using driving cycles representative of different levels of urban traffic, determined by statistical methods on the basis of data detected on-road by an instrumented car. For each driving cycle, representative of a certain traffic level, different thermal starting conditions of catalyst have been tested. These conditions have been determined by the characterization of catalyst performance at steady state and are representative of real catalyst conditions experienced on the road.