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Conversion from diesel to dual fuel (diesel and natural gas) operation may represent an attractive retrofit technique to get a better PM-NOx trade-off in a diesel engine, with no major modifications of the original design. In the proposed paper, an Euro 2 heavy duty diesel engine, converted for dual fuelling, has been studied and tested to reduce pollutant emissions. Throttled stoichiometric with EGR and lean burn technologies have been selected as control strategies. A mixed experimental-numerical approach has been utilized to analyze the engine behavior by varying key operating conditions such as throttling, natural gas/diesel oil percentage and EGR. The model, based on a 3D approach, has been used mainly to understand the evolution of the distribution of the most important parameters in the combustion chamber.

Dual-fuel engines, based on the use of natural gas (NG) as the main fuel in internal combustion engines (ICE) and using diesel injection as the ignition source instead of the spark plug, are one of the possible ways to reduce the trade off PM-NOX problem of traditional diesel engines. The high octane number (NOR) of NG allows to easily covert existing diesel engine, without varying the original compression ratio, with great advantages in terms of costs. The only modifications concern with the introduction of feeding system for NG and the reduction of diesel quantity injected into the combustion chamber, by acting on injection pump control. For high degrees of substitution, diesel oil can be considered only as the ignition source for the fresh air/NG mixture, with consequent beneficial effects on PM emissions. The real drawback regarding dual-fuel engines is the wide increase in HC and CO emissions and efficiency worsening, especially under part-load conditions.

One of the possible solutions in order to reduce NOX and PM emissions and fuel specific consumption in a diesel engine is to substitute a part of the diesel oil with a gaseous fuel. Natural gas, due to the high octane number, allows such substitution without great modifications to the original engine, just introducing the gas feeding system. The utilization of natural gas (usually referred as “alternative fuel”) instead of oil is an important advantage of such technology in terms of energy sources. In this paper the conversion of the IVECO 8360.46R engine, for bus applications, to dual-fuel operations is discussed. Experimental tests were performed to define the general behaviour of the engine, especially at partial loads. Main target of the present study was the analysis of engine requirements to maintain the same output load as the full-diesel operation, and controlling exhaust emissions.

Two stoke engine for mopeds and motorcycles is reaching an important appointment for its survival. In fact, already with the introduction of EURO 1 emission limits, it was necessary to modify some components of the propulsion apparatus in order to reduce especially the huge amount of HC emissions, due to the mixture losses during the scavenging. It was demonstrated that an effective solution to lessen emissions, including benzene, from current two stroke engines for two wheelers, could be retrofitting circulating vehicles with a catalyst. But this is not enough to comply the future more stringent European limits. A powerful solution has been suggested by an important Italian two wheeler manufactures based on the direct injection of gasoline, during the compression stroke, when the exhaust port is closed. The engine is described in the paper, in terms of performance and emissions, and the main results are reported.

In the frame of the IEA-AMF, Annex XVII project ‘Real Impact of New Technologies for Heavy Duty Vehicles’, three state-of-the-art city bus technologies were evaluated for fuel consumption and emissions in real city traffic and in a number of test cycles, both on engine and on vehicle level. One of the three buses was a natural gas bus with multi-point fuel injection, stoichiometric fuel control and three-way catalyst. Compared to the other tested technologies, this engine reached very low exhaust gas emissions. The paper will discuss the results obtained with the stoichiometric natural gas engine and compare the emissions in real traffic versus various engine test cycles, based on a number of influencing parameters. Concerning cycle characteristics it was the distribution of the engine operating points which had most effect on the exhaust gas emissions.

Natural gas has a favorable effect on both the engine performance and emissions. The heavy duty vehicles fueled with natural gas have very low emission levels, not easily obtainable with other fuels, and therefore they are considered the most practicable EEV (Enhanced Environmental Friendly Vehicles). Moreover, the assessment of fuel availability makes its use possible for a long time, whilst the new generation of feeding systems offers solutions to the problem of fuel composition variability. Nevertheless, the positive environmental aspects often are not totally known by people involved in natural gas application, therefore some limitations in the diffusion of this fuel in the transportation sector still appear. This paper refers about the activities, under development at the Istituto Motori, aimed to evaluate the toxicity of engine exhausts gas, based on the analysis of components harmful to human health, such as the carbonyl compounds, PAHs and particulate matter.

The use of Compressed Natural Gas as an alternative fuel in urban transportation is nearly established and represents an efficient short and medium term solution to face with urban air pollution. However, in order to completely exploit its potential, the engine needs to be specifically designed to operate with this fuel. In the latest years, the authors have investigated the performances of a Heavy Duty Turbocharged CNG fuelled engine both experimentally and by using some analytical tools specifically developed by them which have been used for the engine optimisation. In the present paper the simulation approach has been enlarged by means of a co-operative use of a CFD code and experimental analysis on the actual engine. The numerical simulation of combustion process has, in fact, been used, to interpret series of pressure cycles, aiming to analyse how cyclic fluctuations influence engine behaviour in terms of combustion efficiency and temperature and pollutant distribution.

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.

Three developmental catalytic converters, provided by different companies, were tested at the exhaust of a SI (spark ignition) NG (natural gas) engine for bus application. The catalysts were all based on noble metals: Pt (platinum), Pd (palladium), Rh (rhodium) and differed in size, metal loading and active phase composition. Emission evaluation was performed according to the European ECE-R49 procedure (13 mode cycle), in stoichiometric and lean-burn conditions. In addition to regulated emission measurement, speciation of NMHC (non-methane hydrocarbons) and carbonyl compounds was performed. The results showed that all the catalyst compositions considered allowed the European emission limits to be complied when the engine operated in stoichiometric conditions, while the overall best performance in the lean region was obtained on the catalyst with noble metal composition Pd:Rh=21:1.

Natural gas is a viable alternative fuel to obtain low exhaust emissions. A heavy duty DI Diesel engine was converted to Otto cycle natural gas operation. Two alternative solutions were compared: lean-burn technology; stoichiometric feed with three-way catalyst and EGR. Power and efficiency were similar for the two above solutions, and exhaust temperature resulted similar to the diesel engine in both cases due to the diluted operation. The lean bum engine met EURO II ECE-R49 limits except for total hydrocarbons. Stoichiometric engine emissions resulted much lower than the limits. Particulate emissions were quite negligible for the two solutions.