hh i g h l i g h t s

The new dual injection system can easily vary Use of higher amount of n-butanol even at pa Vaporization improved by proper targeting of

to knocload w

Phase separationsimultaneously injected into the intake manifold using this dual injection system. Experiments areconducted at different fuel ratios and throttle positions at an equivalence ratio of 1. The system results in

used as the sole fuel and also in the blended formwith gasoline in SIengines. Due to their limited availability in many countries alcoholscannot be used to completely replace gasoline. Further, the use of100% alcohol will need changes in engine parameters and

alcohols may notconditions. Theseith gasoline in theed with the use ofith the amount of

, difculty in coldstarting due to their high latent heat, phase separation of the blendeven in the presence of small amounts of moisture and corrosive-ness [1e4]. While using pre blended alcohol and gasoline it will notbe feasible to vary the proportions of these two fuels based on theoperating conditions which can vary rapidly in an automotive en-gine. Hence, methods other than blending have to be devised toovercome these problems and to achieve good performance.

Amongst alcohols, butanol is being evaluated for its suitabilityto be used in spark ignition (SI) engines as its properties are close

* Corresponding author. Tel.: 91 9865705078.E-mail addresses: venuengines@gmail.com, venugopal.thangavel@gmail.com

Contents lists available at

Applied Therma

ev

Applied Thermal Engineering 59 (2013) 550e558(T. Venugopal).1. Introduction

The use of alcohols as fuels has gained importance due to theirlow global warming potential, good combustion characteristics andavailability. In general, alcohols are good spark ignition (SI) enginefuels on account of their high octane number. Alcohols have been

materials. It is also to be noted that use of neatensure proper combustion at certain operatingfactors have led to the use of alcohols along wblended form. There are also problems associatalcohols in engines like changes in performancewalcohol used along with gasoline in the blendamounts of n-butanol reduced the tendency to knock. Hence, with the dual injection system n-butanolcan be effectively used along with gasoline.

2013 Elsevier Ltd. All rights reserved.Alcoholsn-ButanolFuel ratio and emissions

good vaporization of the fuels even at low load conditions because the fuel jets are aligned to hit differentportions of the intake valve. Results indicate that with proper selection of the fuel ratio signicantreduction in HC emissions can be achieved as compared to operation on neat gasoline. Up to 60% of n-butanol could be used at 15% throttle while up to 80% could be used at 25% throttle. These proportionsare higher than what have been achieved by pre-blending these fuels. The possibility of using high Neat n-butanol reduced the tendency Engine torque can be improved at full

a r t i c l e i n f o

Article history:Received 12 April 2013Accepted 13 June 2013Available online 27 June 2013

Keywords:Dual injection1359-4311/$ e see front matter 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.applthermaleng.2013.06.02the ratio of alcohol and gasoline.rt loads is possible with new system.fuel sprays and HC emissions reduced.k at full load by charge cooling.ith n-butanol as compared to gasoline.

a b s t r a c t

In spark ignition engines fuelled by alcohol gasoline blends, the proportion of the two fuels has to bevaried according to the operating condition. Further high amounts of alcohol cannot be blended withgasoline because the two phases can separate under certain conditions. In this work a dual injectionsystem, wherein n-butanol and gasoline can be injected separately in any ratio has been employed in aspark ignition engine. The objective is to determine the most suitable amounts of n-butanol and gasolineto be used at different operating conditions of a four stroke spark ignition engine when these fuels areIC Engines Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, Tamilnadu 600 036, IndiaEffective utilisation of butanol along witengine through a dual injection system

T. Venugopal*, A. Ramesh

journal homepage: www.elsAll rights reserved.6gasoline in a spark ignition

SciVerse ScienceDirect

l Engineering

ier .com/locate/apthermeng

Nomenclature and units

CA crank angle ()CO carbon monoxide (% vol)COV co-efcient of variance (%)HC hydrocarbon (ppmv)HRR heat release rates (J/CA)IMEP indicated mean effective pressure (bar)IVO inlet valve opens (IVO)MBT minimum advance for best torque (CA before TDC)NO nitric oxides (ppmv)SI spark ignitionTP throttle positionWOT wide open throttlephi equivalence ratio

Notation for fuels

T. Venugopal, A. Ramesh / Applied Thermto those of gasoline. High energy content, high ame velocity,relatively low latent heat of evaporation and low corrosiveness arethe major advantages of n-butanol [1,2,5e8]. Conventionalfermentation processes can be used to produce n-butanol. Meta-bolic reaction of bacteria or yeast in the absence of oxygen canproduce n-butanol. Starch and glucose are converted into alcoholsand other by-products like carbon-di-oxide, hydrogen and acids[2,9,10]. The properties of gasoline, n-butanol and ethanol areshown in Table 1. The octane number of n-butanol is close to thevalue of gasoline. Its higher latent heat of evaporation is benecialin reducing oxides of nitrogen (NOx) as the temperature of thecharge will be low. The fuel bound oxygen in n-butanol will reducethe hydro carbon (HC) and carbon monoxide (CO) emission levels[1,5,8]. However, not much work on the use of n-butanol as an

B n-butanolIB iso-butanolE ethanolM methanolengine fuel has been reported in literature. Hence, in this work n-butanol was chosen as the fuel to be used in different proportionswith gasoline.

An electronically controlled dual injection system that wasdeveloped by the authors has been used in this work to simulta-neously inject alcohol and gasoline into the intake port of a SI

Table 1Properties of gasoline, ethanol and n-butanol [2,3,5&6].

Property Gasoline Ethanol n-Butanol

Chemical formula C4eC12 C2H5OH C4H9OHComposition (C, H, O) (mass %) 86, 14, 0 52, 13, 35 65, 13.5, 21.5Lower heating value (MJ/kg) 42.7 26.8 33.1Density (kg/m3) 715e765 790 810Octane number ((R M)/2) 90 100 87Boiling temperature (C) 25e215 78 118Latent heat of vaporization

(25 C) (kJ/kg)380e500 904 716

Self-ignition temperature (C) z300 420 343Stoichiometric air/fuel ratio 14.7 9.0 11.2Laminar ame speed (cm/s) z52 63 57Mixture caloric value (MJ/m3) 3.75 3.85 3.82Ignition limits in air (vol %)Lower limit 0.6 3.5 1.4Upper limit 8 15 11.2Solubility in water at 20 C

(ml/100 ml H2O)

consumption or online blending can also be used to avoid phaseseparation. An online fuel blending systemwas developed by usingseparate tanks for ethanol and gasoline and a stepper motor basedcontrol valve with a mixing chamber. Performance and emissioncharacteristics with E70 (70% ethanol in gasoline) were observedto be better than gasoline and E10 [19]. Online mixing of the twofuels in a carburettor is also one solution. Rapid changes in theequivalence ratio are difcult in a carburettor during transientconditions [20].

There was no major change torque in the range of compressionratios between 8 and 11:1 with ethanol blends namely, E20, E40and E60 at full throttle; whereas torquewas increased with amountof ethanol in the blend at higher compression ratios of 12 and 13:1.Highest torque was observed with E60 at the compression ratio of13:1 at wide open throttle due to the high antiknock quality ofethanol [21]. The torque and exhaust gas temperature were re-ported to be similar among all the three isomers of butanol.However, changes in emission characteristics were found [22].

On the whole it is seen that pre-blended alcohol-gasoline fuelscannot offer the best performance at all operating conditions. Thussystems which can vary the ratio of the fuels online are required.The present work evaluates the performance, emissions and com-bustion characteristics of an automotive SI engine fuelled with

varying amounts of butanol and gasoline using a dual injectionsystem capable of online variations in fuel ratio.

3. Experimental setup

A four stroke, single cylinder, air cooled automotive engine witha compression ratio- 9.4:1, displacement volume of 200cc and arated power of 6.5 kW @ 5000 rpmwas used for this study. Torquewas applied andmeasured by using an eddy current dynamo-meterwith closed loop control of speed. The air ow rate was measuredby using a roots type airow meter (DRESSER Inc. USA). A plenumwas used to dampen the uctuations in the ow rate at the air owmeter. This plenumwas located between the engines air lter andthe air owmeter as seen in Fig. 1. NO emissions were measured bya chemiluminescence analyser (Rosemount, USA). HC and COemission measurements were taken using a Non-Dispersive Infra-Red (NDIR) analyser (Horiba, Japan). Water vapour in the exhaustgas was condensed before emission measurements. Fuel ow rateswere measured by precision weighing balances on the mass basis.The temperature of the fuels was maintained at a constant value byusing small heat exchangers. A ush mounted Piezo-electric pres-sure transducer (Kistler 6052C, Switzerland) and an angle encoder(Kubler, Germany) with special data acquisition software

T. Venugopal, A. Ramesh / Applied Thermal Engineering 59 (2013) 550e558552Fig. 1. Schematic of experimental set up.

developed in-house were used to capture cylinder pressure data onthe angle basis along with a (National Instruments, USA) dataacquisition system.

Cylinder pressure data were averaged for hundred cycles andused for the calculation of heat release parameters based on therst law of thermodynamics during closed valve period [23]. TheHohenbergs correlation was used to calculate heat transfer to thewalls of the combustion chamber for the estimation of heat releaserates [24]. The mean in-cylinder gas temperature was calculated bythe ideal gas law. Initially, the mean cylinder charge temperature atthe start of compression was calculated based on adiabatic mixingof the trapped residual gases at exhaust gas temperature andinducted fresh charge of air and fuel. Stoichiometry was used tocalculate the composition of the burned products for the calcula-tion of properties [25]. A real time engine controller that can beused for any type of engine (Universal Engine Controller - UEC) thatwas developed in the laboratory using a National Instruments FPGA(Field Programmable Gate Array) hardware and software written inLabview was used to control the ignition timing, injection quantity(pulse width) of the injectors and also the injection timing. Typicalvalues of uncertainties calculated with 95% condence level forbrake thermal efciency, HC, CO and NO emissions are 0.6%,12 ppmv, 0.04% vol and 50 ppmv respectively [26].

The schematic layout of the experimental set up is shown inFig. 1.Two solenoid based fuel injectors were located on a newly

operating conditions. Experiments were conducted at 15, 25, 35and 100% throttle positions which correspond to 45, 60, 75 and 85%volumetric efciencies respectively. The speed of the engine waskept at a constant value of 3000 rpm. The closed valve injectionstrategy was followed as this has been reported to reduce HCemissions [27,28]. The injection timing of both the fuels was keptconstant and the entire injection process occurred when the intakevalve was closed. The pulse widths of the signals supplied to thetwo injectors located on the intake port were varied online by theengine controller to obtain any fuel ratio that was required and alsoto maintain the equivalence ratio at 1.

It may be noted that the injectors need to supply awide range ofow rates in the case of simultaneous injection, because of varia-tions in the load (throttle) and also in the fuel ratio. Due to this largerange of ow rates, it was found that even with the smallest of theavailable injectors a reduction in the injection pressure was neededfor proper functioning of the injectors. This variation in injectionpressure was needed when the throttle position was 25% or lowerwhile the fuel ratio was lower than 20% or greater than 80%. Thisensured that the widths of the electrical pulses applied on the in-jectors were always greater than 1.5 ms for their stable operation.Low pulse widths lead to irregular operation of fuel injectors. Sinceinjection was done in the closed valve period as with practicalsystems, both the fuels impinged on the back of the intake valveand hence injection pressure is not expected to inuence perfor-

ratio of butanol is 60% by mass of the total mass of gasoline andbutanol. The letter S indicates simultaneous injection in order to

T. Venugopal, A. Ramesh / Applied Thermal Engineering 59 (2013) 550e558 553designed manifold in such a way that sprays do not hit the walls ofthe manifold but impinge on the back of the intake valve for goodvaporisation [27,28] as shown in Fig. 2. With two injectors, almostthe entire surface of the valve is effectively utilized for vaporizationof the fuel.

4. Experimental procedure

Experiments were conducted by varying the proportions of n-butanol and gasoline from 0 to 100% by mass (0, 20, 40, 60, 80,100%) using the dual injection system described earlier. Theequivalence ratio (phi) was kept at 1 (stoichiometric) and the sparktiming was set at the minimum advance for best torque (MBT) at allFig. 2. Location ofdifferentiate from injection of conventional pre-blended fuel usinga single injector. The symbol phi indicates the overall equivalenceratio based on both fuels injected. The term fuel ratio indicated inmance signicantly. The temperature of the fuel was maintainedat a constant value (between 29 1 C) by using small heatexchangers.

5. Results and discussion

In the following graphs and discussions B60S indicates that thethe injectors.

performance. The best spark timings were generally more

Fig. 4. Variation of engine torque and volumetric efciency vs. fuel ratio (100%Throttle).

hermal Engineering 59 (2013) 550e558some graphs is the mass percentage of butanol in the total amountof fuel (n-butanol and gasoline) that is injected.

The caloric values per unit mass of various mixtures of n-butanol and gasoline are shown in Fig. 3. As the fuel ratio increases,the contribution of gasoline to the caloric value of the mixturereduces and that of n-butanol increases. The caloric value of themixture decreases with increasing fuel ratio. It is due to the inferiorheating value of n-butanol as compared to gasoline. At a fuel ratioof approximately 60%, equal energies are contributed by both fuels.The stoichiometric air fuel ratio decreases from 14.7:1 to 11.2:1when the fuel ratio increases from 0 to 100%. This is because thestoichiometric air fuel ratio for n-butanol (11.2:1) is lower than thatof gasoline (14.7:1) due to the presence of oxygen in themolecule ofthe former fuel. At a given equivalence ratio, the use of higheramounts of n-butanol due to its low air requirements compensatespartially for its inferior heating value. The heating value of n-butanol is 33.1MJ/kg which is 22.5% lower than the heating value of

Fig. 3. Variation of heating value and fuel energy supply vs. fuel ratio.

T. Venugopal, A. Ramesh / Applied T554gasoline (42.7 MJ/kg). The total energy supplied by both the fuels(fuel mixture) with respect to fuel ratio of n-butanol and gasoline isshown in Fig. 3 for 1 kg of air and the corresponding chemicallycorrect quantity of fuel. It is clear from Fig. 3 that when the fuelratio increases, the amount of heat supplied by the fuel mixtureincreases due to increase in the total mass of fuel mixture suppliedper kg of air. This is because of the lower stoichiometric airrequirement of n-butanol as compared to gasoline. A decrease involumetric efciency (based on air inducted by the engine) withfuel ratio was observed at 100% throttle as shown in Fig. 4. Highermass ie higher number of moles of n-butanol are used as comparedto gasoline for the same equivalence ratio. This will mean thatduring the vaporization of the fuel more air will be displaced by n-butanol as compared to gasoline which lowers the volumetric ef-ciency. Such a drop in volumetric efciency has also been reportedin the case of blends of 85% ethanol and gasoline blends [29]. Wesee in Fig. 4 that the torque increased with fuel ratio even thoughthe volumetric efciency decreased by about 2.5%. This is becausethe heat added by the fuel per unit mass of air increases with fuelratio at constant equivalence ratio.

The variation of brake thermal efciency with fuel ratio isshown in Fig. 5. Nomajor change in efciency was observed at 100%throttle. Even though torque was increased with fuel ratio at 100%throttle, the heat added by the fuel per unit mass of air was alsoincreased. This is the reason for similar brake thermal efciencies at100% throttle with increasing torque, when the fuel ratio increased.The thermal efciency of the engine did not change until a fuel ratioof 60% ie B60S at 15% throttle. Use of higher amounts of n-butanol(B80S and B100) reduced the efciency due to inferior fuel vapor-ization at the low torque or throttle conditions where the compo-nent temperatures are low. The efciency with B100 was around1.5% and 1% lower than that with gasoline at 15% and 25% throttlesrespectively. It should also be noted that a single injector was onlyused for B100. In this case the fuel will hit only a part of the valveand vaporization will not be as effective as when two injectors areused. The temperatures of the engine components were also lowerat part throttle which also hindered vapourization of n-butanol.This trend was conrmed by repeated experiments. At all otherthrottle positions no major changes in efciency were observedwith different fuel ratios. Hence, it is better to use up to B60S at 15%throttle and not to use B100 at 15 and 25% throttles to ensure goodFig. 5. Variation of brake thermal efciency vs. fuel ratio.

Fig. 6. Variation of spark timing vs. fuel ratio.Fig. 8. In-cylinder pressure vs. crank angle (100% Throttle).

T. Venugopal, A. Ramesh / Applied Thermal Engineering 59 (2013) 550e558 555advanced when the fuel ratio was increased at 35% and 100%throttle positions (Fig. 6). These spark timings were knock limited.Use of more amount of n-butanol reduced the in-cylinder tem-perature which allowed the spark timings to be more advanced bymitigating the knock. The higher ame velocity of n-butanol ascompared to gasoline also could be the reason for that. At thethrottle position of 15%, the ignition timing had to be retarded withincrease in the fuel ratio because of the reduction in temperature ofthe charge when increasing amounts of n-butanol were used.

The heat release rates are also higher with B60S as compared togasoline as seen in Fig. 7 at 15% throttle. Higher heat release rates

with B60S are due to better utilization of valve heat by proper

Fig. 7. Heat release rate vs. crank angle (15% Throttle).targeting of the fuel sprays on the different portions of the intakevalve. A lower combustion duration was observed with B60S(59CA) as compared to gasoline (64CA). The in-cylinder pressuretraces and heat release rate vs. crank angle are shown in Figs. 8 and9. The peak cylinder pressure becamehigherwhen the fuel ratiowasincreased at 100% throttle position. This is due to more advancedknock limited spark timing with n-butanol. The heat release rateswere also higher and more advanced with increase in fuel ratio.There was nomajor difference in 10e50%mass burn durationwhenthe fuel ratio was changed (maximum difference of 3 CA) at 35%and 100% throttle position (Fig. 10). However, the crank angle atwhich 50%burn duration occurs is found to be earlierwith increasedfuel ratio due to advancement of the spark timing. Co-efcient ofFig. 9. Heat release rate vs. crank angle (100% Throttle).

T. Venugopal, A. Ramesh / Applied Thermal Engineering 59 (2013) 550e558556variance (COV) of indicatedmean effective pressure (IMEP) was lessthan 4% at all operating conditions. COV of peak pressure was be-tween 6 and 10% at different fuel ratios. No major variation in 10e90% mass burn duration (combustion duration) was observed withchanges in fuel ratio. Similar results were also reported in studiesusing conventional pre-blended butanol and gasoline [5,8,13].

Hydrocarbon (HC) emissions were appreciably reduced whenthe fuel ratio was increased, in general. It was reduced by around15% with B60S at 15% throttle as compared to gasoline due to bettermixture preparation on account of effective utilization of the heatin the valve. The two sprays in the case of simultaneous injectionfall on different regions of the intake valve and thus enable better

Fig. 10. 10e50% mass burn duration and CA@50% mass burn duration occurs vs. fuelratio.vaporization of the fuels. The fuel bound oxygen in n-butanol couldalso be the reason for low HC emissions. Further, addition of

Fig. 11. HC emission vs. fuel ratio.butanol at 15% throttle increased the HC emissions (Fig. 11). This isattributed to lack of vaporization of n-butanol with B80S and B100at 15% throttle where the engine component and cylinder gastemperatures were low. This limit was extended to a fuel ratio of80% ie B80S at 25% throttle. A 33% reduction in HC emissions withB80S was observed at 25% throttle as compared to operation withgasoline. In the case of higher throttles like 35 and 100%, increase inthe fuel ratio progressively lowered the HC level as seen in Fig. 11.HC emissions were reduced by 27% and 41% at 35% and 100%throttles respectively with B100 operation. Temperatures of theengine components and the gas in the cylinder are high at highthrottles and they aid vaporization of the fuel. Low exhaust tem-

Fig. 12. NO emission vs. fuel ratio.peratures that were observed with B100 at part throttle will reducepost oxidation and lead to higher tail pipe HC emissions [5,12,13].

Fig. 13. In-cylinder gas temperature vs. crank angle (35% Throttle).

T. Venugopal, A. Ramesh / Applied ThermMost of the earlier studies reported that the HC emissions wereincreased when blends of more than 40% of n-butanol with gaso-line by volume were used in SI engines [5,12,13]. However, thepresent dual injection system has resulted in signicantly reducedHC emissions due to improved fuel vaporization by effectivelyutilizing the valve heat evenwith higher fuel ratios at part throttle.No major changes in CO emissions were observed with differentfuel ratios due to stoichiometric operation.

In general, NO emission was reduced when the fuel ratio wasincreased at high throttles like 35% and 100% as seen in Fig. 12. Thehigh latent heat of butanol is effective in reducing the temperatureof the charge (Charge cooling) and this leads to low NO emissions[5,8]. Specically, at 35% throttle position, the NO level showed asmall rise beyond B80S. This was observed during repeatedexperimentation. It may also be noted that even though the peakin-cylinder temperature for gasoline (B0), B80S and B100 at 35%throttle were almost similar as seen in Fig. 13, the NO levels weredifferent in all these three cases. The adiabatic ame temperature ofgasoline is higher than butanol. Hence, even though the mean gas

Fig. 14. Cylinder peak pressure vs. fuel ratio.temperatures were almost similar between the different fuels, theNOx emission was higher for gasoline. Low NO emissions wereobserved with B100 at 15% and 25% throttles due to inferior com-bustion. Similar results were also observed in earlier studies con-ducted by the present authors with different injectors. Literatureindicates that NO emission reduces when using 40% of n-butanol byvolume or higher as compared to gasoline in the pre blended form[5,12,13]. However, in this work with the use of two injectorswherein the valve heat effectively vaporizes the fuel, there is a dropin NO emission only at higher fuel ratios.

The cylinder peak pressures were increased, when the fuel ratiowas raised particularly at high throttles (Fig. 14). It is due to more

Table 2Suitable amount of n-butanol for lowest emission.

Throttle(%)

Best fuelratio(% by mass)

Change in efciencyin comparison togasoline

HC emission (%)decrease ascompared togasoline

NO emission (%)decrease ascompared togasoline

15 60 Similar 15% Similar25 80 Similar 33% Similar35 100 Similar 27% 10%100 100 Similar 41% 7%advanced knock limited spark timing that could be used ascompared to gasoline. The effect of charge cooling and higher amevelocity of n-butanol result in more advanced spark timings.Similar trends were observed at part throttle except for B100. Basedon the performance and emission characteristics using the simul-taneous injection system, the most suitable amounts of n-butanolto be injected for different throttle positions are xed in compari-son to neat gasoline operation as shown in the Table 2.

In general, the performance and emission characteristics ofn-butanolegasoline mixture with equal energy supply (B60S)produced same efciency and lower HC and NO emissions ascompared to gasoline.

6. Conclusions

It is important to change the ratio of butanol to gasoline basedon the throttle position for obtaining low HC emissions. Thiscould be easily achieved with the present dual injectionsystem.

The maximum torque of the engine increased as the fuel ratioof n-butanol was rised. With 100% butanol the torque increasesby 2% even though the volumetric efciency decreases byabout 2.5% at full throttle operation.

Without any drop in thermal efciency up to B60S could beused at 15% throttle, B80S could be used at 25% throttle. Athigher throttle positions B100 is suitable. High amounts ofbutanol than normally reported with blends could be usedsince the dual injection system utilized valve heat effectivelyfor vaporization of the fuels.

The simultaneous injection systemthrough the useof the properfuel ratio led to a signicant decrease in the HC levels. Re-ductions of 33%, 27% and 41% in HC emissions were observed25%, 35% and 100% throttles respectively with the correct fuelratios.

There was a general decrease in NO emissions with highbutanol fuel ratios. No signicant change in CO emissions wasfoundwith different fuel ratios, since stoichiometric conditionswere maintained during these experiments.

The knock limited spark timings were more advanced becauseof the reduction in the charge temperature with butanol. Thisenabled higher torques to be achieved. Higher ame speed andmore advanced knock limited timing produced higher peakcylinder pressures when the butanol fuel ratio was increased.

On thewhole the developed simultaneous injection system is aneffective way to utilize n-butanol or other alcohols along withgasoline based on operating conditions. In situations where theavailability of alcohols is restricted they could be used with the dualinjection system only when high torque or high reductions in HCemissions are needed during actual operation.

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T. Venugopal, A. Ramesh / Applied Thermal Engineering 59 (2013) 550e558558

Effective utilisation of butanol along with gasoline in a spark ignition engine through a dual injection system1 Introduction2 Background3 Experimental setup4 Experimental procedure5 Results and discussion6 ConclusionsReferences