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Hydrogen addition to ethylene and acetylene -air laminar diffusion flames has shown substantial reduction in soot formation. In the present study, hydrogen was carbureted in a single cylinder, naturally aspirated DI diesel engine, and combustion events and smoke emissions were studied. With hydrogen induction particularly when its energy share increased above 15%, contrary to the results reported by earlier investigators a sharp decrease in ignition delay (ID), very high peak pressure rates, increase in smoke and loss in fuel efficiency were observed. At hydrogen energy share of about 30%, ignition delay drops to nearly 0-1degree CA and peak rates of pressure rise to 25-30 bar/deg CA. Smoke emissions at low hydrogen induction rates reduced slightly but increased sharply above 15 to 20% hydrogen energy share.

Emission regulations for portable generator sets have been enforced in India from June 2000 and more stringent standards since 2001. Studies on application of catalytic converters on two-stroke gasoline and 4-stroke kerosene fuelled SI engine generator sets were carried out in addition to lean tuning of the engines for making these compliant with the emission standards currently in force and likely to be implemented in the coming years. The kerosene fuelled generator sets are set for very rich operation to obtain smooth combustion and hence an air blower had to be employed for injection of the high amount of required secondary air for functioning of oxidation catalysts resulting in 77 to 88% reduction in HC (hydrocarbons) and CO (carbon monoxide) emissions By lean tuning and catalytic converter optimization 74 to 89% reductions in HC and CO emissions were obtained on the 2-stroke generators even without secondary air.

Decarbonization of transport fuels initially happened to store more energy on board of transport vehicles. As most vehicular emissions are carbon containing chemical species, now the emission regulations are providing impetus to this trend through reduction in aromatic and olefin content of petroleum fuels and move towards use of gaseous fuels; natural gas, LPG and finally to hydrogen. In this paper trends in transport fuels and effect of their chemical composition and hydrogen/carbon ratio on emissions especially the particulate (PM), nitrogen oxides (NOx) and green house gas emissions are discussed.

Emission regulations for portable generator sets have been enforced in India from June, 2000 and more and more stringent standards are in offing. Studies on application of monolith and packed bed oxidation catalytic converters on a two-stroke gasoline and 4-stroke kerosene fuelled SI engine generator sets were carried out. Substantial reductions in HC (unburned hydrocarbons) and CO (carbon monoxide) emissions were obtained on the 2-stroke generator even without secondary air and it could meet the June 2001 standards. For functioning of the catalytic converters on kerosene generator, secondary air had to be introduced. Although, significant reduction in CO were obtained, for improving conversion of HC, improvements in catalyst formulation and optimization of secondary air are to be done.

Current and future emission standards in the USA has provided motivation for development of alternative energy vehicles. Hybrid-electric (HEV), fuel cell (FCV) and electric vehicles (EV) are under development. HEVs and FCVs are capable of operation on commercially available fuels and have long enough range. Present day gasoline and diesel engines are strong contenders for use as prime movers for HEVs. FCVs with on-board fuel-reformers to produce hydrogen are under development for commercial production in the next few years.

The influence of fuel characteristics on particulate emissions has been widely investigated. In this paper, the effect of different fuel properties on particulate emissions has been reviewed. The effect of fuel sulphur has been reported to have linear-relationship with the sulphate content of particulates. Combustion system, engine loading etc. were found to have weak contribution to the sulphate content variation. The results and analysis of various studies showed that the aromatic content had little influence on particulate emissions particularly in DI engines of modern design. The results from a number of investigations show that the key fuel property influencing particulate matter (PM) is the density.

Injector nozzles of direct injection diesel engines (DI) of in-service vehicles showed one or more holes blocked and significant flow reduction even in nozzles with all the holes open. Coked nozzles from field gave measurable increase in smoke, carbonmonoxide (CO) emissions and specific fuel consumption (BSFC). Tests of 500 hour duration on a naturally aspirated DI diesel engine revealed hardly any significant nozzle coking particularly with the fuels containing total cycle oil (TCO). In some cases, an increase in flow rates in nozzles was observed for in-service vehicles as well as in 500 hour engine tests. In the long duration tests, statistically significant increase only in CO and reduction in NOx emissions were observed with a straight run diesel fuel and another fuel containing 20% TCO. Change in power, BSFC and HC emissions during 500 hour engine operation were not significant with any of the test fuels.

Hydrocarbon composition of fuel affects the deposit composition, its capacity to heat up the hot spots, and propensity of the fuel to preignition. Presently, fluidized catalytically cracked streams forms a large fraction of total gasoline pool in India and gasolines contain up to 50% olefins. About 60% of total gasoline in the country is consumed by the two wheeled vehicles powered mostly by 2-stroke engines. Preignition tendency of fuels with varying content of olefinic hydrocarbons was studied on a 2-stroke engine, during a 50 hour test. Preignition was indicated by sudden increase in combustion chamber surface temperature. Results showed a marked increase in preignition as the olefin content of gasoline increased above 20% by volume.

The matching of fuel injection characteristics with air motion and combustion chamber geometry is now widely modelled for more rigorous investigations of fuel-air, mixing in direct injection (DI) diesel engines to obtain improvements in fuel economy and emission characteristics. A number of studies have contributed in the understanding of fuel spray-air motion interaction in DI diesel engines. The genesis and characterization of swirl motion both during induction and compression is discussed as it influences spray growth, its trajectory and fuel-air mixing. Different aspects of fuel spray structure eg. break-up, drop-size distribution, spray penetration, air entrainment etc. are important. These spray development aspects are also briefly discussed in the paper. Different analytical approaches to model air entrainment in turbulent jet in the engine situation are summarized.

A mathematical model based on turbulent gas jet theory was used to study spray-swirl interaction in direct injection diesel engine. Vectorial approach was used to predict the momentum change in two directions (i) along the spray centre-line and (ii) normal to the centre-line. Effect of changes in air density and swirl velocity during compression was accounted for. Effect of different injection parameters viz. nozzle size, injection rates, duration of injection, shape of injection rate curve, location of injector in the cylinder head and spray angle was studied on spray penetration, spread, air entrainment and momentum ratio of spray to air etc. Initial rate of injection and mass averaged injection pressure play significant role in air-fuel mixing for spray injected from side of the cylinder, whereas the initial rate of injection dominates the mixing for central injection. Nozzle orifice size does affect fuel-air mixing but it is predominantly controlled by the injection pressure.

Research on conversion of diesel engines for operation on methanol is, currently, of worldwide interest. Due to requirements of higher cyclic delivery of methanol and changes in fuel properties e.g. compressibility, wave propagation velocity, viscosity, surface tension, density etc., injection and atomization characteristics of methanol are expected to be different from diesel. From the equation of continuity and forces acting on the injection system elements and applying the principles of similarity, modifications required in the injection system were identified. Methanol injection and atomization characteristics were studied with a modified injection system and compared with those observed with diesel fuel. Methanol gave more favourable cyclic delivery characteristics than diesel. Laser diffraction technique was used to study time and space resolved drop size distribution in methanol and diesel sprays.

The influence of charge non-homogeneity on the cycle-by-cycle variations in combustion for a SI engine was studied experimentally and analyzed theoretically. Charge non-homogeneity was determined from the exhaust gas composition. Cycle-by-cycle variations in the maximum combustion pressure and the angle of maximum pressure were determined by using a real time data acquisition system. A linear relationship between charge non-homogeneity and the cyclic variations in maximum pressure was found. Computed results showed that cyclic variations in maximum combustion pressure increase with increase in charge non-homogeneity at a given mixture strength. For the same charge non-homogeneity, cyclic variations also increase with leaning of the mixture and with increase in the duration of initial phase of combustion.