! "# $ % & ’ & ! (& # ( !"#"$" )* Laser ignition of wet ethanol was carried out at equivalence ratio of 0.8. Additions of water in ethanol up to 20% (v/v) accelerated the combustion rate with shorter laser ignition delay compared to dehydrated ethanol. + * (140.3440) Laser%induced breakdown; (120.1740) Combustion diagnostics; (280.5475) Pressure measurement ,- Concern about global warming is growing all over the world and as a consequence ethanol has long been considered as a good internal combustion engine fuel. To reduce the greenhouse gas emission from internal combustion engine, biomass fuel such as ethanol, methanol, n%butanol, ETBE (ethyl tertiary%butyl ether); have been focused as an attractive alternative fuel instead of gasoline in an SI engine. Some studies have reported that ethanol has a higher flame velocity compared to gasoline/iso%octane and lower combustion temperature which reduces heat loss to the combustion chamber walls, therefore higher thermal efficiency can be achieved [1]. The high production cost of anhydrous ethanol (99.9% purity) is associated with the energy spent in distillation and dehydration process to remove water, perhaps up to 37% of total energy input [2] which leads to the use of wet ethanol. Previous study has shown that removing the final 20% of water (and particularly the final 5%) from ethanol requires the greatest fraction of energy; therefore, direct use of wet ethanol in engines could improve the associated energy balance. Recently, laser%induced ignition method seems to be one of the most promising alternatives ignition source to replace the conventional spark ignition system. Laser ignition system has some potential advantages like variable ignition location and multi%point ignition can be performed with precise control over ignition timing and energy [3, 4]. Absence of electrode minimizes the heat loss during flame kernel development. In addition, Laser ignition offers the opportunity for sudden release of specific radicals and the onset of specific reactions [4]. In previous study on laser ignition of premixed fuel and air mixture, the process of flame kernel formation is investigated and the role of OH radicals is discussed in detail [5]. Recently experimental study on interaction between laser%induced plasma and fuel spray were conducted [6]. Authors previously investigated the laser ignition characteristics of stratified charge of hydrous ethanol at stoichiometric condition [7]. The primary objective of this study is to investigate the effect of water content on lean combustion (equivalence ratio, ɸ = 0.8) characteristics of premixed charge of wet ethanol ignited by laser%induced breakdown. Time%series images of combustion flame were obtained through visualization by high%speed camera. Analyses on in%chamber pressure history, mass fraction burned, initial combustion duration and laser ignition delay were conducted for comprehensive understanding. .- At first fuel is injected to the constant volume chamber through a DISI 6%hole injector; and for premixed ignition, an electric heater with magnetic stirrer is used to attain premixed charge of fuel%air by facilitating the evaporation and mixing of ethanol with the ambient air inside the chamber and to maintain the preheat temperature (unburnt mixture temperature) of 380 K. Laser%induced plasma was generated for the ignition of wet ethanol by focusing a nanosecond pulse of second harmonic (wavelength λ=532 nm, beam diameter d = 8 mm, pulse duration = 8 ns) of Q%switched Nd:YAG (Spectra Physics, Lab series%150) laser. Incident beam (E in = 30 mJ) was adjusted by a half% wave plate and a polarizing beam splitter, and the laser beam was focused using a plano%convex lens with focal length of 100 mm. The chamber has optical access through quartz window which makes possible the visualization of plasma generation and subsequent flame propagation by using a high%speed camera (nac Image Technology Inc., MEMRECAM GX%8) at 10,000 frames per second. /- 01 2-3 In order to determine the better or optimum stirring duration for the laser ignition of premixed charge of ethanol%air, preliminary tests were carried out for dehydrated ethanol and then extended for ethanol with different concentration of water. Based on the results from pressure history, high speed imaging and flame spectra, 40 minutes stirring