An Optical Study of Spray Development and Combustion of Ethanol, Iso-Octane and Gasoline Blends in a DISI Engine

Abstract

In recent times regulatory pressure to reduce CO 2 emissions has driven research towards looking at blending fossil fuels with alternatives such as crop-produced alcohols. The alcohol of interest in this paper is ethanol and it was studied in mixtures with gasoline and iso-octane in an optical sparkignition engine, running at 1500 RPM at low-load operation with 0.5 bar absolute intake plenum pressure. Specifically, tests involved fuels of 100% gasoline and 100% iso-octane, so that differences between multi and single-component fuels could be compared within this environment. A mixture of 25% ethanol with 75% iso-octane was also tested and compared. Finally, mixtures of highpercentage of ethanol (85% ethanol) in gasoline and in iso-octane were used in the study and compared. Tests were undertaken using a standard port injection system as well as a direct injection system so an appraisal of both mixture preparation methods could be made. Initially, a high-speed imaging study of the in-cylinder spray formation was undertaken with the direct injection system for different injection timings and engine-head temperatures under motoring engine conditions. The engine was also run with continuous firing using all fuels. In-cylinder pressure data were collected at 0.2° crank angle resolution for each cycle and synchronized with simultaneous high-speed flame imaging at 1° crank angle resolution for a series of 100 consecutive cycles for all test points. The flame images were processed to quantify the evolution of an equivalent flame radius.

Characterisation of flame development with ethanol, butanol, iso-octane, gasoline and methane in a direct-injection spark-ignition engine

“…In addition, the percentage of ethanol in the total fuelling played a dominant role in affecting the combustion characteristics at light load; however, at full load the DI fuelling percentage became the important parameter, regardless of the percentage of ethanol in the fuel. Some of these findings are different to those of Aleiferis et al [13] with PFI and DI fuelling which showed that DI increased the rate of heat release in general with both gasoline and gasoline/ethanol blends at low-load conditions. One reason for this discrepancy might be that Zhu et al [12] used a low pressure multihole side injector with a nine-hole orifice plate at 20 bar injection pressure compared to the swirl-injector at 80 bar used in [13].…”

Modulation of integral length scales of turbulence in an optical SI engine by direct injection of gasoline, iso -octane, ethanol and butanol fuels

“…However, these were set to match nominally as nearly as possible those of previous work published on this engine by the current authors on spray formation and combustion with various fuels, e.g. [18]. The load at 1500 RPM was controlled by throttling to 0.5 bar (±0.01 bar) absolute pressure in the intake plenum.…”

“…All timings given in °CA refer to the 'crank angle time equivalent' at 1500 RPM, with one 1 °CA corresponding to 0.111 ms. 1500 RPM corresponded to a mean piston speed of 4.25 m/s. More details about the engine can be found in previous publications [17][18][19].…”

“…The fuel was supplied to the injector by a Heypac GX30 pneumatic pump and regulator; the injection pressure was fixed at 80 bar. The injection timing was fixed to 60 °CA ATDC (after intake TDC) for 'homogeneous' mixture preparation; this was based on earlier work with various injection timings and fuels that had optimised injection timing in order to allow maximum time available for evaporation up to ignition timing but also minimise piston-crown spray impingement during injection [18]. The injection duration was adjusted for stoichiometric Air-to-Fuel Ratio (AFR) conditions according to a wide-range lambda sensor and AFR1200 recorder.…”

Flame front analysis of ethanol, butanol, iso-octane and gasoline in a spark-ignition engine using laser tomography and integral length scale measurements

“…Therefore, extended discussion will form part of a separate dedicated publication on the basis of [61] where flow field changes with fuelling were studied over a range of conditions and linked by a combination of factors, such as the duration of injection, the droplet velocities and droplet sizes during injection, the fuel spray's shape during injection (e.g. see [19] for spray 'collapse' effects in this engine), etc.…”