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In-cylinder optical diagnostic was applied to study butanol-gasoline blend combustion in a SI engine. Spark timing and fuel injection mode were changed to work in normal and knocking conditions. The experiments were realized in a single-cylinder ported fuel injection SI engine with an external boosting device. The engine worked like-stoichiometric mixture at 2000 rpm, medium boosting and wide open throttle. UV-visible natural emission spectroscopy allowed to follow the formation and the evolution of the main compounds and radical species that characterize the combustion process from the spark ignition until the exhaust. Particular interest was devoted to OH and CO₂* evolution, and to the spectral evidence of soot precursors due to fuel deposits burning. OH resulted the best marker for combustion both in normal and abnormal conditions.

In the present paper, results of an experimental investigation carried out in a modern Diesel engine running at different operating conditions and fuelled with commercial diesel and n-butanol-diesel blend are reported. The investigation was focused on the management of injection strategy and combustion timing (CA50) exploring the effect of intake oxygen concentration and boost pressure on engine out emissions. The aim of the paper was to compare, with respect to commercial diesel, the effects of a fuel blend with a lower cetane number and higher volatility on performance and engine out emissions. Engine tests, with baseline diesel and a blend made by the baseline low sulphur diesel with 20% in volume of n-butanol (B20), were performed comparing engine out gaseous, smoke emissions and combustion efficiency. The investigation was performed on a turbocharged, water cooled, DI diesel engine, equipped with a common rail injection system.

Multi-wavelength ultraviolet-visible extinction spectroscopy was applied to follow the evolution of fuel vapor injected by post-injection along the exhaust line of a common-rail turbocharged direct-injection diesel engine at moderate speed and load. The exhaust line was specifically designed and customized to allow the insertion of the optical access upstream of the Diesel Oxidation Catalyst. During the experimental campaign, the engine was fuelled with commercial B5 fuel and a B30 v/v blend of RME and ultra low sulfur diesel, monitoring emissions upstream of the catalyst and exhaust gas temperature across the catalyst. Tests were performed at different engine operating conditions with particular attention to moderate speed and load.

One promising approach to reduce pollutants from compression ignition engines is the Partially-Premixed- Combustion in which engine out emissions can be reduced by promoting mixing of fuel and air prior to auto-ignition. A great interest for a premixed combustion regime is the investigation on fuels with different reactivity by blending diesel with lower cetane number and higher volatility fuels. In fact, fuels more resistant to auto-ignition give longer ignition delay that may enhance the fuel/air mixing prior to combustion. During the ignition delay period, the fuel spray atomizes into small droplets, vaporizes and mixes with air. As the piston moves towards TDC, as soon as the mixture temperature reaches the ignition point, instantaneously some pre-mixed amount of fuel and air ignites. The balance of fuel that does not burn in premixed combustion is consumed in the rate-controlled combustion phase, also known as diffusion combustion.

This paper reports results of an experimental investigation performed on a commercial diesel engine supplied with fuel blends having low cetane number to attain a simultaneous reduction in NOx and smoke emissions. Blends of 20% and 40% of n-butanol in conventional diesel fuel have been tested, comparing engine performance and emissions to diesel ones. Taking advantage of the fuel blend higher resistance to auto ignition, it was possible to extend the range in which a premixed combustion is achieved. This allowed to match the goal of a significant reduction in emissions without important penalties in fuel consumption. The experimental activity was carried on a turbocharged, water cooled, 4 cylinder common rail DI diesel engine. The engine equipment included an exhaust gas recirculation system controlled by an external driver, a piezo-quartz pressure transducer to detect the in-cylinder pressure signal and a current probe to acquire the energizing current to the injector.

Optical imaging and UV-visible detection of in-cylinder combustion phenomena were made in a single cylinder optically accessed high swirl multi-jets compression ignition engine operating with two different fuels and two EGR levels. A commercial diesel fuel and a lighter fuel blend of diesel (80%) and gasoline (20%), named G20, were tested for two injection pressures (70 and 140 MPa) and injection timings in the range 11 CAD BTDC to 5 CAD ATDC. The blend G20 has a lower cetane number, is more volatile and more resistant to the auto-ignition than diesel yielding an effect on the ignition delay and on the combustion performance. Instantaneous fuel injection rate, in-cylinder combustion pressure, NOx and smoke engine out emissions were measured. Taking into account the particular configuration of the engine, the efficiency was estimated by determining the area under the working engine cycle.

This paper reports results of an experimental investigation to demonstrate the potential to employ blends of fuels having low cetane numbers that can provide high resistance to auto-ignition to reduce simultaneously NOx and smoke. Because of the higher resistance to auto-ignition, blends of diesel and gasoline at different volume fraction may provide more time for the mixture preparation by increasing the ignition delay. The result produces the potential to operate under partially premixed low temperature combustion with lower levels of EGR without excessive penalties on fuel efficiency. In addition to the diesel fuel, the tested blends were mixed by the baseline diesel with 20% and 40% of commercial EURO IV 98 octane gasoline by volume, denoted G20 and G40. The experimental activity has been performed on a turbocharged, water cooled, DI diesel engine, equipped with a common rail injection system.

The addition of alcohol to conventional hydrocarbon fuels for a spark-ignition engine can increase the fuel octane rating and the power for a given engine displacement and compression ratio. In this work, the influence of butanol addition to gasoline was investigated. The experiments were performed in an optical ported fuel injection single-cylinder SI engine with an external boosting device. The engine was equipped with the head of a commercial SI turbocharged engine having the same geometrical specifications (bore, stroke and compression ratio). The effect of a blend of 20% of n-butanol and 80% of gasoline (BU20) on in-cylinder combustion process was investigated by cycle-resolved visualization. The engine worked at low speed, medium boosting and wide open throttle. Changes in spark timing and fuel injection phasing were considered. Comparisons between the flame luminosity and the combustion pressure data were performed.

To meet the future stringent emission standards, innovative diesel engine technology, exhaust gas after-treatment, and clean alternative fuels are required. Oxygenated fuels have showed a tendency to decrease internal combustion engine emissions. In the same time, advanced fuel injection modes can promote a further reduction of the pollutants at the exhaust without penalty for the combustion efficiency. One of the more interesting solutions is provided by the premixed low temperature combustion (LTC) mechanism jointly to lower-cetane, higher-volatility fuels. In this paper, to understand the role played by these factors on soot formation, cycle resolved visualization, UV-visible optical imaging and visible chemiluminescence were applied in an optically accessed high swirl multi-jets compression ignition engine. Combustion tests were carried out using three fuels: commercial diesel, a blend of 80% diesel with 20% gasoline (G20) and a blend of 80% diesel with 20% n-butanol (BU20).

The air fuel mixing process of a small direct injection (d.i.) diesel engine, equipped with two different re-entrant combustion chambers and two nozzles having unlike spray angles, has been studied by integrated use of in-cylinder laser Doppler velocimetry (LDV) measurements, engine tests, and KIVA simulations. The LDV measurements have been carried out in an engine with optical access motored at 2200 rpm. The engine tests have been performed on a similar engine at the same speed, at fixed start of combustion, and different air-fuel ratio. The KIVA-II simulations have been made using as initial conditions the parameters determined by LDV and engine tests. The re-entrant bowl with higher levels of air velocity and turbulent kinetic energy at the time of injection gives the best performance. The nozzle having a spray angle of 150° which injects the fuel into the regions at higher turbulent kinetic energy lowers the smoke emission levels.