Search Results

The effect of different fuel parameters on emissions is difficult to understand, the response depending upon different engine technologies. In addition the isolation of some of the fuel variables is often very hard. The present paper discusses the main results obtained testing a matrix of 14 fuels designed for obtain large variations of cetane number, sulphur and aromatic contents of Diesel oil. The aromatic structure of fuels and its effect on particulate emissions was also investigated. A linear regression analysis was performed in order to isolate the main controlling factors on particulate emissions. Finally the influence of aromatic contents of fuel on unregulated emissions was also assessed.

Three dimensional computations of Diesel combustion were performed using a modified version of Kiva II code. The autoignition and combustion model were tuned on a set of experimental conditions, changing the engine design, the operating conditions and the fuel characteristics. The sensitivity of the model to the different test cases is acceptable and the experimental trends are well reproduced. In addition the peak of pressure and temperature computed by the code are quite close to the experimental values, as well as the pressure derivatives. Once tuned the combustion model constants, different but simple formulations for the soot formation and oxidation processes were implemented in the code and compared with the experimental measurements obtained both with fast sampling technique and two colors method. These formulations were found unable to give good prediction in a large range of engine operating conditions, even if the model tuning may be very good for each test point.

In the present paper the status of development of diesel combustion and pollutants formation modelling at Diesel Engines and Fuels Research Division of Istituto Motori is pointed out. The main features and performances of the model are discussed comparing the numerical results with some experimental data. For the experiments a single cylinder direct injection diesel engine was used. In the head of the engine two small quartz windows have been mounted, in order to obtain pictures of the injection and combustion processes by high speed cinematography, and to apply the two colour technique for soot temperature and soot loading measurements. The soot loading was measured by the two colour technique and the a priori and the experimental uncertainties of the measurement technique were carefully evaluated. In addition, the engine may be also equipped with a second head, in which a fast acting valve allows the direct sampling of the combustion products.

Unregulated emissions of polycyclic aromatic hydrocarbons (PAHs), carbonylic compounds, benzene and particulate matter (PM) were quantified in exhausts of a vehicle fleet representative of in use gasoline cars. Emission factors were obtained during both cold and hot start driving cycles (from urban to motorway driving conditions). Carbonylic compounds were sampled by DNPH cartridges and analyzed by HPLC. Benzene and other light hydrocarbons were collected in bags and then analyzed by GC-FID. PAHs were trapped in XAD-2 cartridges and then analyzed by GC-MS. PM was sampled by using the gravimetric procedure required for diesel cars. The effect of technology is significant with respect to regulated and unregulated emissions but different emissive behavior was found by varying the driving cycles. Cold start has a major influence on hydrocarbon emissions (included unregulated ones). This experimental work was carried out within the framework of the EU Artemis project.

The attention on emissions of two-wheelers has been poor in the past, but today in countries with a large two-wheeler population it gives a significant contribution to aggregate emissions. In this paper the results obtained on a fleet composed by 22 two-stroke motorcycles (including mopeds) are presented. Sixteen in-use mopeds and six 125 cm3 motorcycles have been tested over ECE 47 and ECE 40 driving cycles respectively. Regulated emissions (CO, HC, NOx), carbon dioxide, benzene and fuel consumption have been evaluated by fueling motorcycles with two different gasoline formulations. One gasoline was a commercial Italian leaded gasoline with 1% benzene content; the other was a lower benzene and aromatics content gasoline. Benzene emissions decreased according to benzene content of gasoline.

The contribution to environmental pollution due to mopeds and motorcycles equipped with 2-stroke engines is very high. Then European regulations will impose in the next future severe limits on pollutant emissions of such vehicles. Up to 40% of the charge at high load and low speed can be lost during scavenging, therefore exhaust hydrocarbon speciation is similar to fuel composition, i.e. with a comparable content of benzene. The use of rich air-fuel mixtures, necessary to reduce cyclic variations and improve driveability during transients, determines also high carbon monoxide emissions. On the other hand NOx emissions are very low in all operating conditions, due to the rich mixtures and the high residual gas fraction. An effective solution to reduce emissions from current two-stroke engines for two wheelers in a short time could be retrofitting circulating vehicles with a catalyst for exhaust after-treatment.