using dual injection of n-b

T. Venugopal, A. Ramesh Mechanical Engineering Department, Indian Institute of

h i g h l i g h t s

l and gciencyor neatlet valves the H

at the fuels hit the back of the intake valve. The engine was fully instrumented

All rights reserved.

1. Introduction

Several alternative fuels like ethanol, butanol, methanol, biodie-sel, natural gas, liqueed petroleum gas and hydrogen are beinginvestigated for their use in internal combustion engines. Bio-fuelslike bio-alcohol have the potential to control net global CO2 emis-sions and also to reduce consumption of fossil fuels. Alcohols can

be used as fuels for spark ignition (SI) engines due to theantiknock quality, high ame velocity and because of the prof oxygen in their molecule that helps combustion. Amongshols, n-butanol is an emerging renewable fuel which can be pro-duced from biological sources. A comparison between theproperties of gasoline, ethanol and 1-butanol which is also knownas n-butanol is shown in Table 1. Butanols caloric value and stoi-chiometric air fuel ratio are close to those of gasoline. Its latentheat of evaporation is higher than gasoline. It is also less corrosivethan other alcohols [13]. The wide ammability limits and high Corresponding author.

Fuel 115 (2014) 295305

Contents lists available at

ue

.eE-mail address: aramesh@iitm.ac.in (A. Ramesh). 2013 Elsevier Ltd.0016-2361/$ - see front matter 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.fuel.2013.07.013ir goodesencet alco-Simultaneous injectionBut50SInjection timingInjection phasing

for the measurement ofperformance, emissions and combustion parameters. Initially experiments wereconducted with simultaneous injection of n-butanol and gasoline (1:1 mass ratio = But 50S) using the twoinjectors with different injection timings at 25% and 60% throttle positions at 3000 rpm. Subsequently dif-ferent injection timings for the two fuels were tried to study the inuence of sequencing. The results werecompared with gasoline and n-butanol (But100) using a single injector. Around 26% reduction in hydro-carbon (HC) emission with simultaneous injection of gasoline and n-butanol (But50S) at 25% and 60%throttle positions was observed with an injection timing of 64 CA before in let valve opening as com-pared to open valve injection. B100 was superior at high throttle positions and gasoline or B50S was suit-able at 25% throttle as regards performance and emissions. At 60% throttle, injecting n-butanol just beforethe start of injection of gasoline is benecial for reducing HC andcarbon monoxide (CO) emissions. In thecase of lean operation (equivalence ratio of 0.82) there is no signicant inuence of injection phasingexcept for a small improvement in thermal efciency. On the whole this method of operating the enginecan lead to good engine performance over wide operating conditions since the ratio of the fuels can bevaried.Keywords:n-Butanol

n-butanol separately so th System of varying blend ratio of alcoho n-Butanol improves the torque and ef Use of n-butanol blend (50% by mass) Completing fuel injection before the in Injection phasing or sequence inuenc

a r t i c l e i n f o

Article history:Received 3 September 2012Received in revised form 1 July 2013Accepted 2 July 2013Available online 19 July 2013utanol and gasoline in the intake port

Technology Madras, Chennai, India

asoline was developed.at higher throttle position.gasoline is good at lower throttle than neat n-butanol.e opens reduced HC emission.C and CO emissions little.

a b s t r a c t

Alcohols can be used in spark ignition (SI) engines along with gasoline in the blended form. However,phase separation which occurs in the presence of moisture restricts the amount of alcohol that can beblended. On the other hand, for effective engine operation, the ratio of alcohol to gasoline has to be variedbased on the engine operating condition. n-Butanol has properties close to gasoline and has not beenwidely investigated as an engine fuel. In this work, two injectors were mounted in the intake port ofan automotive SI engine (bore = 62 mm, stroke = 66 mm, compression ratio = 9.4) to inject gasoline andExperimental studies on the effect of injection timing in a SI engineF

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lower CO levels were observed with blends of n-butanol as com-

Nomenclature

BSFC brake specic fuel consumption (g/kW h)BTE brake thermal efciency (%)But100 n-butanolBut50S n-butanol and gasoline by 1:1 mass ratio simulta-

neouslyCA crank angle ()CO carbon monoxide (% vol)CO2 carbon dioxide (% vol)COV co-efcient of variance (%)FPGA Field Programmable Gate ArrayHC hydrocarbons (ppmv)HRR heat release rate (J/ CA)

MBD mass burn duration ( CA)MBT minimum advance for best torque ( CA before TDC)NDIR non-dispersive infraredNI National InstrumentsPP peak pressure (bar)NOx oxides of nitrogen (ppmv)SI spark ignitionTDC top dead centreUEC universal engine controller/ equivalence ratio (actual fuel air ratio by stoichiometric

fuel air ratio)

296 T. Venugopal, A. Ramesh / Fuel 115 (2014) 295305pared to gasoline, HC emission levels were higher at low loads[7]. Tests with ethanol gasoline blends showed that at 20% throttleand low speeds (3000 rpm) E05 (5% Ethanol and 95% gasoline byvolume) gave the highest torque and at high speeds E30 was thebest. At 40% and 60% throttles, E20 and E30 were observed to bethe best. At high throttle conditions no clear trend was observed[8].ame speed of n-butanol will allow the engine to operate with leanmixtures, high thermal efciency and low cycle by cycle variations[36]. Only limited studies have been conducted on n-butanol in SIengines. Hence, in this work the performance of n-butanol in dif-ferent proportions along with gasoline using a dual injection sys-tem was evaluated in a SI engine.

2. Background and objective

In experiments conducted on n-butanol in SI engines, blends upto But40 (40% n-butanol and 60% gasoline by volume) performedsimilar to gasoline. However, Hydrocarbon (HC) and carbon mon-oxide (CO) emissions were higher for blends like But60 andBut80. Emission levels of Nitrogen oxides (NOx) were lower dueto the high latent heat of evaporation of n-butanol [6]. Lower com-bustion duration was also recorded with the blends as compared tooperation on neat gasoline [3,7]. No differences in HC, CO and NOxemissions were observed between But10 and gasoline [1]. Though

IMEP indicated mean effective pressure (bar)IVO inlet valve opensAlcohol gasoline blends can separate in the presence of water.However, the stability of blends of n-butanol and gasoline is goodeven in the presence of moisture. This is because of the low

Table 1Properties of gasoline, ethanol and n-butanol [1,2,4].

Property G

Chemical formula CComposition (C, H, O) (mass%) 8Lower heating value (MJ/kg) 4Density (kg/m3) 7Octane number ((R + M)/2) 9Boiling temperature (C) 2Latent heat of vaporization (25 C) (kJ/kg) 3Self-ignition temperature (C) Stoichiometric air/fuel ratio 1Laminar ame speed @1 bar, 393 K, = 1.1 (cm/s) Mixture caloric value (MJ/m3) 3Ignition limits in air (vol%)Lower limit 0Upper limit 8Solubility in water at 20 C (ml/100 ml H2O)

alcoholgasoline ratios even under transient conditions. Such asystem will also allow the blend ratio to be changed in real time.However, details of such operation with two injectors are not re-ported in literature. The objective of this study is to explore theperformance, emission and combustion characteristics of a SI en-gine with injection of gasoline and n-butanol through two injectorsinto the intake port at varying injection timings and injection phas-ing or sequence. The results have been compared with neat gaso-line and neat n-butanol which were injected through a singleinjector. It was expected that injection phasing or sequencing ofthe timing of start of injection of the two fuels could lead to chargestratication when one fuel is injected at the closed intake valvecondition and the other fuel is injected when the intake valve isopen. Hence, the effect of injection phasing or sequencing theinjections of gasoline and n-butanol was also studied in this work.

3. Experimental set up and procedure

The schematic of the experimental setup used for this work isshown in Fig. 1. The specications of the engine and the injectorsare given in Tables 2A and 2B respectively. The engine was coupled

to an eddy current dynamometer equipped with a closed loopspeed controller. Air Flow rate was measured by using a roots typeairow meter (DRESSER Inc.USA, Model 2M175). Exhaust gas

Table 2ASpecications of the engine.

Engine 3 wheeler auto engine (TVS King)No. of cylinders/cycle One/4 StrokeIgnition system Spark ignitionBore Stroke 62 mm 66 mmConnecting rod length 120 mmDisplacement volume 200 ccCompression ratio 9.4: 1Rated power 6.5 kW @ 5000 rpm with gasolineCooling medium Air cooledLubrication system Pressurized lubricationOil sump capacity 1.75 lLubricating oil SAE 20W40

Number of valves 2Intake valve opening 26 bTDC (694 CA)Intake valve closing 44 aBDC (224 CA)Exhaust valve opening 48 bBDC (492 CA)Exhaust valve closing 22 aTDC (22 CA)

T. Venugopal, A. Ramesh / Fuel 115 (2014) 295305 297Fig. 1. Schematic of the experimental set up.

/ FuTable 2BSpecications of the injector.

Number of holes 4Spray cone angle 15 with gasoline

13.5 with n-butanolFlow rate (DP = 3 bar, 10 ms) 16.9 mg/injection (gasoline)

17.7 mg/injection (n-butanol)Injector location 94 mm from the inlet valve centre

Table 2CUncertainty of parameters.

Dynamometer torque and speed 0.13 N m and 3 rpmEfciency 0.6%Equivalence ratio 0.03Blend ratio of n-butanol 1.5%Exhaust gas temperature 4 CHC 12 ppmvCO 0.04 %volNO 50 ppmvPeak pressure 1 bar

298 T. Venugopal, A. Rameshemissions were measured by calibrated emission instruments(NO-based on a Rosemount USA make chemiluminescence ana-lyzer, HC and CO based on a NDIR analyzers of Horiba Japan make).Fuel ow rates (both n-butanol and gasoline) were measured usingprecision weighing balances on the mass basis. A ush mountedPiezo-electric engine pressure transducer (Kistler, Switzerland,Type 6052C) and an angle encoder (Kubler, Germany) were usedwith specially developed software. A National Instruments (NI,USA) data acquisition system was used with this software to cap-ture cylinder pressure data on the angle basis. An average of 100cycles of cylinder pressure was used for the calculation of heat re-lease parameters. Heat release rates were calculated based on therst law of thermodynamics as applied during the period wherethe intake and exhaust valves are closed (closed valve period)[16]. Heat transfer was calculated using the Hohenbergs correla-tion with an assumed wall temperature of 400 K [17]. Literatureindicates that the experimentally measured values of heat uxesmatch closely with the Hohenberg correlation [1820] and hencethis correlation was used in this work for the calculation of wallheat transfer. Initially, the mean cylinder charge temperature atthe crank angle where the inlet valve closes was calculated basedon adiabatic mixing of trapped residual exhaust gases at exhaustgas temperature and inducted fresh charge of air and fuel at ambi-ent temperature. The mean in cylinder gas temperature at different

Fig. 2. Important crank angles and valve timings.crank positions was calculated by the ideal gas law. The composi-tion of the burned products was calculated based on completecombustion for the calculation of properties [21]. An universal en-gine controller (UEC) that was developed in the laboratory usingNational Instruments FPGA (Field Programmable Gate Array) hard-ware along with in-house developed software written in Labviewwas used to control the injection timing and injection quantity(pulse width of the signal given to the injectors). All experimentswere conducted at 25% and 60% throttle positions at 3000 rpm. Aspecial intake manifold incorporating two fuel injectors, one forgasoline and the other for n-butanol was developed and used. Carewas taken to orient the injectors such that the sprays do not hit thewalls of the manifold but only impinge on the back of the intakevalve for good vaporization. Typical values of uncertainties of dif-ferent parameters with 95% condence level [22] are given inTable 2C.

In the rst phase of experiments, the injection timing (start ofinjection) was varied from 0 to 720 CA. Here the same injectiontiming was kept for both the injectors. In this case 0 CA indicatesthe angle at suction top dead centre (TDC) and 720 is one com-plete cycle (i.e. two revolutions). This is the notation that was fol-lowed for the rst phase of experiments. The inlet valve opens at694 CA i.e. 26 CA bTDC (before TDC) and closes at 224 CA(Fig. 2). Hence, when the injection timing was varied, fuel injectionoccurred during the closed valve, open valve and combined closedvalve-open valve periods of engine operation. The ratio of themasses of the two fuels was maintained at 1:1. Experiments werealso conducted with neat (100%) gasoline and neat n-butanol usinga single 0.82 injector. In the above experiments the equivalence ra-tio was maintained at 1. After ndingthe best injection timing, thesecond phase of experiments was done. This was a study of the ef-fect of injection sequencing in a narrow range of injection timingswhich were near the inlet valve opening (IVO) point i.e. certain de-grees of crank angle before and after IVO as given in Table 2D. Thiswas again done at a xed fuel mass ratio of 1:1 (n-butanol to gas-oline) at an equivalence ratio of 1. Here the start of injection ofeither gasoline or n-butanol was kept xed at 630 CA (64 CA be-fore inlet valve opening (IVO)) as this was found to be optimal fromthe experiments in Phase 1. The injection timing of the other fuelwas varied from about 150 CA before IVO to about 150 CA afterIVO at 60% throttle. This range was kept narrow at 25% throttle(Table 2D), since the pulse widths used were lesser as comparedto those at 60% throttle.Subsequently the inuence of phasingthe injection of the two fuels was also studied with lean mixturesat an equivalence ratio of 0.82 and 60% throttle opening. In allcases the spark timing was set at the minimum advance for besttorque (MBT) using the FPGA controller.

4. Results and discussion

The results of experiments conducted in the rst phase i.e. withsimultaneous injection (same start of injection for both n-butanoland gasoline injectors) are presented and discussed below.

4.1. Simultaneous injection at 60% throttle position (Phase 1)

Figs. 37 indicate the inuence of injection timing on perfor-mance, emissions and combustion when the engine was operatedwith gasoline, n-butanol and n-butanol + gasoline (But50S i.e. n-butanol and gasoline injected through separate injectors butsimultaneously in the mass ratio 1:1). As seen in Fig. 3a, injectiontimings with But50S do not have a signicant inuence on brakethermal efciency. Similar trends were seen in the case of torque

el 115 (2014) 295305also. At 60% throttle, neat butanol (But100) leads to higher torqueand efciency than gasoline and But50S because of faster combus-tion at all injection timings. This is because of the higher ame

/ FuTable 2DEngine operating conditions.

T. Venugopal, A. Rameshspeed of n-butanol. The best spark timing which is also knock lim-ited, was more advanced with butanol because of the reduction incharge temperature due to vaporization of the fuel. It may be notedthat n-butanol has a higher latent heat of vaporization than gaso-line and also a lower caloric value. The ability to use higher spark

Experiments Range of injection timin

Effect of injection timing (Fuel ratio = 0, 50 and 100) 0720Effect of injection sequence (Fuel ratio = 50) 150 bIVO to 150 aIVO

94 bIVO to 26 aIVO64 bIVO to 86 aIVO

Fig. 3. (a) Brake thermal efciency vs. injection timing and (b)el 115 (2014) 295305 299advances without knock in the case of n-butanol has led to betterthermal efciency and torque.

The brake specic fuel consumption (BSFC) was higher forBut100 due to its low energy density or heating value on the massbasis as compared to gasoline. BSFC values of But50S were in

gs for gasoline and n-butanol Throttle positions Equivalence ratio

25% and 60% 160% 125% 160% 0.82

HC and NO emissions vs. injection timing (60% throttle).

Fig. 4. Heat release rate and mean cylinder gas temperature vs. crank angle (a) 630 CA injection timing (60% throttle), (b) 0 CA injection timing (60% throttle), and (c) 630CA injection timing (25% throttle).

Fig. 5. Spark timing and combustion parameters (60% throttle).

300 T. Venugopal, A. Ramesh / Fuel 115 (2014) 295305

/ FuT. Venugopal, A. Rameshbetween gasoline and But100. Typical values of BSFC were 304,337.5 and 381.5 g/kW h for gasoline, But50 and But100respectively at 60% throttle and at the best injection timing of630 CA (64 CA bIVO). n-Butanol has higher hydrogen to carbonratio (2.5:1) as compared to gasoline (2.25:1). This is the reasonfor the low CO2 emission levels with n-butanol. The CO2 emissionlevels at 60% throttle were 13.9%, 14% and 13.2% for gasoline,

Fig. 6. (a) NO emissions vs. injection timing (25% throttle)

Fig. 7. COV of IMEP and COV of peak pressel 115 (2014) 295305 301But50S and But100 respectively at best injection timing of 630CA (64 CA bIVO). Similar trends were also found at 25% throttleposition. The increase in CO2 emission with But50S was probablydue to better combustion with the twin injection system. It maybe notedthat the HC emission with But50S at this condition is low-er than But100. Similar trends have also been reported with blendsof ethanol with gasoline [8,23].

, (b) HC emissions vs. injection timing (25% throttle).

ure vs. injection timing (25% throttle).

There is a signicant inuence of injection timing on HC emis-sions with But50S (Fig. 3b). Injecting the fuel at 630 CA i.e. at640CA before IVO leads to the lowest HC levels (134 ppmv). Itmay be noted that at this condition the injection duration is 54CA which means that the injection is just completed before the in-take valve opens. Here, back ow of hot exhaust into the intakemanifold when the intake valve opens will aid vaporization ofthe fuel [24]. The maximumHC level was observed with open valveinjection of 0 CA (180 ppmv). It may be noted that at this condi-tion, some of the injected fuel will directly enter the cylinder with-out hitting the valve. Faster combustion was observed at thiscondition leading to higher cylinder pressures which could resultin increased ow of fuel into the crevices in the combustion cham-ber and hence elevated HC levels [24,25]. Since stoichiometricoperation was maintained there was no signicant observationwith respect to CO and NO levels. HC, CO and NO emissions arenot greatly inuenced by injection timing in the case of neat gaso-

line and neat n-butanol operation. However, n-butanol exhibitshigher CO levels due to the inuence of lower charge temperatureswhich can affect fuel vaporization. It was also noted that the ex-haust gas temperatures for n-butanol were 5565 C lower thanBut50S and gasoline which could reduce post oxidation of HCand CO in the exhaust. The variation of NO is seen in Fig. 3b. NOemissions of But50S and gasoline were higher than But100 dueto higher charge temperatures. NO emission with But50S wheretwo injectors were used was similar to gasoline due to improvedvaporization. This is probably because in the case of But50S thespray covered a greater portion of the inlet valve as compared togasoline that was injected with one injector. Such results havebeen observed by the authors earlier under different operatingconditions [26].

Heat release rates occurred earlier with But100 as compared togasoline and But50S due to more advanced spark timings (Fig. 4a)at the injection timing of 630 CA (closed inlet valve injection).

302 T. Venugopal, A. Ramesh / Fuel 115 (2014) 295305Fig. 8. Brake thermal efciency and NO emission vs. injection timing (a) 60% throttle, (b)25% throttle.25% throttle and HC and CO emissions vs. injection timing, (c) 60% throttle, and (d)

However, the peak heat release rates were comparable. Heat re-lease was more advanced with But100 and But50S than gasolinedue to earlier spark timings. We see that the peak mean gas tem-perature for But100 is greater than But50S at the injection timingof 630 CA (Fig. 4a). The lowest peak temperature was observedwith gasoline operation. However, the trend of NO was differenti.e. it was higher for gasoline as compared to But50S and But100.This may be due to the differences in the physical and chemicalnature of the fuels used. The post combustion temperature withBut100 is low because of more advanced combustion due to thehigher spark advance that was needed. The low post combustiontemperature affects the oxidation of HC and CO emissions in thecase of n-butanol. As seen in Fig. 4b, with an injection timing of0 CA (open inlet valve injection) the peak heat release rates ofBut100 and But50S are lower than gasoline. Fig. 5 indicates thatthe crank angle at which 50% burn duration occurs is earlier withBut100 and But50S. This is because of the more advanced sparktimings that were used with But100 and But50S. There is no signif-icant difference between the combustion durations of But50S and

gasoline. However, But100 exhibits lower combustion durationson account of faster combustion.

4.2. Simultaneous injection at 25% throttle position (Phase 1)

The efciency of the engine is slightly higher with gasoline andBut50S than But100 as shown in Fig. 3a earlier. The inuence ofinjection timing on efciency and torque is not signicant exceptin the early open valve injection timing of 0 CA where the ef-ciency with But50S is higher than with gasoline and But100. Itmay be noted the in the case of But50S both the injectors (dualinjection) were used and hence the injection pulse duration wasshort (1.7 ms). However, in the case of gasoline and But100 theinjection was done with a single injector and was for much longerdurations (4.2 ms for gasoline and 6 ms for butanol). Thus in thecase of But100 and gasoline the injection of the fuel extends wellinto the intake stroke whereas with But50S the injection pulsestops at about 30 after it starts. A long injection duration well intothe intake stroke will mean that most of the injected fuel is carried

T. Venugopal, A. Ramesh / Fuel 115 (2014) 295305 303Fig. 9. (a) Brake thermal efciency and HC emission vs. injection timing, (b) heat release rate vs. crank angle, and (c) NO emission vs. injection timing.

tures. A difference in efciency and torque was observed at an

of gasoline is benecial for reducing HC and CO emissions thansimultaneous injection (at 60%throttle). However, the difference

/ Fuaway by the inducted air and hence is not effectively vaporized bythe hot intake valve and by the back ow of exhaust gases. Thusvaporization is better with But50S and this results in better heatrelease rate and efciency. Low NO emission was observed withBut100 as compared to gasoline and But50S at 25% throttle, similarto the trends at 60% throttle (Fig. 6a). However, the values of NOwith gasoline and But50S were a little higher at 25% throttle ascompared to 60% throttle due to more advanced spark timings thathad to be used for best torque.

Injecting the fuel at 64 CA before IVO (630 CA) was better inthe case of gasoline and But50S as regards HC emissions(Fig. 6b). Injecting the fuel at 64 CA before IVO resulted in about25% reduction in HC emission as compared to open valve injectionin the case of gasoline and But50S. However, But100 resulted invery high HC levels as compared to gasoline and But50S. With openvalve injection, it is likely that signicant amounts of n-butanolreach the cylinder before vaporization. The exhaust temperaturewas around 5070 C lower with But100 than gasoline and But50S.The lower exhaust gas temperature adversely affects post oxida-tion of HC in the case of But100 as indicated earlier.

The heat release rates were not signicantly inuenced byinjection timing with But50S and gasoline; Lower heat releaserates were observed with open valve injection than closed valveinjection with n-butanol. This is because in the case of injectionwhen the valve is open, the owing air stream carries away the fuelinto the cylinder. However, in the case of closed valve injection(injection when the intake valve is closed) the fuel hits the backof the intake valve and resides there and the hot intake valve effec-tively vaporizes the fuel. This improved vaporization of fuel, resultsin higher heat release rates with closed valve injection. Eventhough higher heat release rates were observed with n-butanolas compared to gasoline and But50S, longer combustion durationand lower post combustion temperature due to charge cooling(Fig. 4c) have led to higher HC emission levels (Fig. 6 b) and lowerefciency. Hence, from the point of view of HC emissions it is notadvisable to use But100 at low throttle conditions. Open valveinjection increased CO emissions with all the three fuels. The co-efcient of variation (COV) of indicated mean effective pressure(IMEP) and the COV of peak pressure (PP) are indicated in Fig. 7.It is seen that there is no signicant variation in these parameterswith changes in the n-butanol ratio and injection timing becausethe operation is at stoichiometric conditions with the best sparktiming.

4.3. Phased injection at 60% and 25% throttle positions (Phase 2)

In these experiments the injection timing of gasoline was xedat 64 CA before IVO and the injection timing of n-butanol wasswept from 150 CA before to 150 CA after the IVO. The samewas repeated with the injection timing of n-butanol being xedand that of gasoline being changed. While this range of injectiontimings was used at 60% throttle position a smaller range 94 CAbefore to 26 CACA after IVO) was used at 25% throttle opening.

No major change in brake thermal efciency was observed withinjection sequence at both the throttle positions. In-general, inject-ing one fuel at open valve condition and the other fuel at closedvalve condition reduced NO emission (Fig. 8a and Fig. 8b). It wasobserved that injecting n-butanol before the start of injection ofgasoline and vice versa produced about 10% lower HC emissions(Fig. 8c) at 60% throttle compared to simultaneous injection of boththe fuels (at 64 CA before IVO). No signicant change in HC and COemissions was observed with injection phasing at 25% throttle(Fig. 8d). Fixing one of the injections at 64 CA before IVO and mov-

304 T. Venugopal, A. Rameshing the other towards the valve open timing increased the COemission due to low post combustion temperatures as discussedearlier (Fig. 8c and 8d). It can be concluded that no major benetsis only about 10%. With lean operation (equivalence ratio of 0.82) there is no sig-nicant inuence of injection phasing except for a smallimprovement in thermal efciency.

On the whole with dual injection n-butanol has to be used athigher throttle positions and gasoline or B50S is suitable at lowerthrottle positions (25%) for good performance and low emissions.Injection timing mainly inuences HC emissions and the bestinjection timing was 64 CA before IVO. Injection phasing has asmall inuence on emissions. Injecting n-butanol just before thestart of injection of gasoline is desirable.

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[2] Owen K, Coley T. Automotive Fuels Handbook. USA: Society of Automotiveequivalence ratio of 0.82 with injection phasing. Injecting one fuelat the IVO point and another one at 64 CA before IVO producedhigher efciency and lower HC emissions as seen in Fig. 9a. Heatrelease rates were observed to be higher with phased injection inthe regions where the efciency is higher as compared to simulta-neous injection (Fig. 9b). Injection phasing could lead to chargestratication which in turn can favorably inuence combustion.Open valve injection can result in charge stratication as reportedin literature [27]. The NO emission level was increased by around15% at the best efciency point as compared to simultaneous injec-tion (Fig. 9c). CO emissions were less than 0.1% vol at all operatingpoints due to operation with lean mixtures (/ = 0.82).

5. Conclusions

Based on the experimental results on injecting n-butanol andgasoline in a SI engine using two injectors the following conclu-sions are made.

n-Butanol improves the torque and efciency at 60% throttleposition by around 1.5% at the best injection timing of 64 CAbefore IVO. However, at the lower throttle position of 25% it isinferior to gasoline and B50S operation. A 1.52% drop in ef-ciency was observed with n-butanol as compared with gasolineat 25% throttle position. It is better to use n-butanol at highthrottle positions and gasoline or B50S at 25% throttle toimprove performance and emission.

Completing fuel injection before the inlet valve opens (i.e. astart of injection of 64 CA before IVO) is best for reducing HCemission. Around 26% reduction in HC emission with simulta-neous injection of gasoline and n-butanol (B50S) at 25% and60% throttle positions was observed. The effect of injection tim-ing on HC emission with 100% n-butanol was found to be less atboth throttle positions.

Injection phasing or sequence mainly inuences the HC and COemissions. Injecting n-butanol just before the start of injectionare there with injection phasing except a 10% reduction in HCemissions at 60% throttle. All the above results are at an equiva-lence ratio of 1.

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T. Venugopal, A. Ramesh / Fuel 115 (2014) 295305 305

Experimental studies on the effect of injection timing in a SI engine using dual injection of n-butanol and gasoline in the intake port1 Introduction2 Background and objective3 Experimental set up and procedure4 Results and discussion4.1 Simultaneous injection at 60% throttle position (Phase 1)4.2 Simultaneous injection at 25% throttle position (Phase 1)4.3 Phased injection at 60% and 25% throttle positions (Phase 2)

5 ConclusionsReferences