Mierset al. (2008) studied effect of 20% and 40% by volume blends ofbutanol-diesel on the performance and emission on an unmodified diesel car insteady state and dynamic operation. Fuel consumption was found to increase withincrease in amount of butanol in the blend. HC and CO emissions found toincrease because of poor combustion efficiency. Smoke emission was found todecrease with increase in amount of butanol in blend.
Influence of butanol addition into diesel fuel was studied with 8%,16% and 24% (by volume) n-butanol amount was used, on theperformance and exhaust emission in a single cylinder four stroke directinjection diesel engine. Three different loads namely 1.4, 2.57 and 5.37 barBMEP were tested at a speed of 2000 rpm while static injection timing was keptat 29 CA before top dead center (bTDC). Smoke and NOx was found to decrease atall loads as amount of butanol increase in blends as compared to neat diesel.However, HC and CO emissions were found to increase with increase in amount ofbutanol in blend.
BTE was found to increase a little this is because higherpremixed combustion because of lower cetane number of blend leads to higherconstant volume combustion. In another study Rakopoulos studied effect ofblends of butanol-diesel (8% and 16% (by vol) n-butanol), on exhaust emissionand performance in a six cylinder turbocharged diesel engine. Addition ofbutanol into diesel reduce cetane number of blend, ignition delay also increasethis increase premixed combustion part and results in better BTE.
Peak of HRRwas higher with blends as compared to pure diesel case. NOx, smoke were foundto decrease with increase in amount of butanol in the blend. However, HC wasfound to increase. Mingfaet al. studied influence of n-butanol in diesel (0, 5, 10 and 15% of butanol byvolume) on emission and performance on a heavy duty diesel engine while blendwas injected into multiple pulses (pilot-main-post). Experiments were conductedat a fixed speed and load however EGR is adjusted to keep NOx emission at 2.0g/kW-hr. They observed that addition of butanol helped in reduction in soot andCO emission without having much impact on BSFC at a constant specific NOxemission in case of single pulse injection.
In addition to this the higher theamount of butanol is blend it resulted in more premixed combustion phase. Indouble injection (pilot and main) for close pilot to main offset soot washigher as compared to single pulse injection of B10. However, as pilot to mainoffset increases soot was found to decrease (reason is not given). CO emissionwas found to increase with pilot to main offset. Post injection with B10, sootand CO emission was found to decrease as main to post offset increase this is becauseof post injected fuel burns and release heat which helps in oxidation of formedsoot.
In case of B10, post injection results in 46.4% (maximum) reduction insoot as compared to single injection. Zhenget al. (2013) studied effect of various blends of butanol-diesel onemissions and performance at different loads in a highspeed direct injection diesel engine. Blends ofdiesel fuel with 0%, 20%, 30% and 40% of butanol (by vol) were directlyinjection into combustion chamber.
With butanol-diesel blends burningrate accelerated and combustion pressure increased this was becauseof ignition-delay increase and this resulted inmore amount of fuel was burning in pre-mixed phase of combustion.However, maximum power and torque was not influencedmuch. In addition to this with blends of butanol-diesel BSFC and BTE both wasfound to increase. Under low loads CO emission increased and NOxdecrease with increase in amount of butanol. However, under high loadopposite trend observed.
Here CO was found to decrease and NOx was found toincrease with increase in amountof butanol. Smoke was found to decrease with increase in amountof butanol at all loads.Choiet al.
(2015) studied influence of blend of n-butanol withdiesel fuel on emission in a turbocharged diesel engine equipped with commonrail direct injection and results were compared with neat diesel case. In thisstudy 0%, 5%, 10% and 20% (by vol)n-butanol blended with diesel. Experiments were performedon European Stationary Cycle (ESC) test, engineperformance and emissions were measured. FourierTransform Infrared Spectroscopy (FTIR) was used to measure emissions of HCs,CO, NOx, HCHO, HCOOH and NH3. ScanningMobility Particle Sizer (SMPS) used to measure Size and number distribution ofparticulate matter (PM). THC and CO emissions werefound to increase with butanol-diesel blends this was because increase inlatent heat of vaporization and decrease in cetane number. Withn-butanol-diesel blends at all operating conditions NOxemission was found to decrease, further with increase in amount ofbutanol NO2 wasincreased.
In NH3-SCR applications NO2is useful in fast reaction of de-NOx system. With B20,HCHO emission were higher at lower loads and lowerat higher loads as compare to neat diesel operation. Withincrease in amount of n-butanol in blends nano-sized PM under 50 nmwere emitted lowered.Onthe whole butanol-diesel forms a stableblends and it helps in simultaneous reductionin NOx and smoke emissions withincrease in BTE. However, HC and CO emissions were found to increase.
2.3.2. Neatbutanol operation in diesel engines –N-butanolhas lower cetane number, high octane number(resistance to auto-ignition) and higher latent heat ofvaporization as compared to diesel these create someproblems in use of neat butanol in a conventionaldiesel engine.
So for utilizing neatbutanol in a diesel engine following methods are employed – A. Injection of butanol along withpreheated air and auto-ignition is governed by air temperature Maurya,2014.B. Port injection of butanolinto air, increase intakepressure of air by boosting it (upto 1 bargauge) so boosting helpsin auto-ignition as it reduces ignition delay Yanai, 2014. C. As boiling point, densityand viscosity are near todiesel fuel butanol can be injected directly athigh pressure into combustion chamber Han, 2013.However,following modification are needed for accommodatingneat butanol as a fuel in diesel engine – A. Port-fuel injection systeminstallation it consists of injectors (gasoline type),fuel pump (injection pressure upto 10 bars) and a fuel tank for storing butanol.
B. As butanol has lowerLubricity then diesel so a Lubricity improvershould be added while using it in a high-pressure injection system for the safety of moving parts Han, 2013. C.
An electric heater isrequired to heat air is requiredif preheated air is used forauto-ignition of butanol which was injected into intake port.D. As butanol is corrosive,rubber and plastic parts have to be replaced with materials which can tolerate alcohols Jin, C.2011. Mauryaet al. 2014-JERT did study on a four cylinder DI diesel engine, one ofwhich was used for research purpose which was havingcompression ratio of 17.5:1, engine wasmodified to run in HCCI mode of operation.
Butanol was injected intointake manifold and homogenous mixture was prepared,preheating of intake-air was used to auto-ignite homogenousmixture of air and butanol. Effect of air-fuel ratio and intake air temperaturewas studied. However, it is noted that whilecalculating efficiency in this study they did notconsidered the amount energy spent in preheating the air. Theyobserved to gasoline has higher operating range forHCCI than butanol. In addition to this gasoline resulted in betterITE (because of better combustion efficiency) and lowerISFC as compared to butanol.
Very lowlevels of NOx emission were observed. However, HC and COemissions were higher as compared to conventional diesel engine. Withincrease in speed operating range for HCCI mode decreased for bothfuels.
Hanet al. (2013) studied use ofn-butanol in a diesel engine using two strategies, i.e.
PFI ofbutanol while disabling DI of diesel and high pressure DI of butanol. In case ofbutanol in PFI mode high amount of EGR (51-57%) required for controllingcombustion phasing and it resulted in ultralow levels of NOx andsmoke emissions. They observed that n-butanolin direct injection under high pressure shows promising results. Near zero sootemissions were observed this wasbecause of longer ignition delay of butanol resulted in better mixture preparation.In addition to this butanol has oxygen atom in its molecule. With moderateintake boost and EGR it was possible to attain IMEP between 1 to1.3 MPa and resulted in simultaneous reduction of NOxand smoke emissions.
However peak pressure rise rate was a problem in extendingload range.Zhenget al. studied n-butanol in HCCI mode in a highcompression diesel engine. Effect of EGR and intake boost oncombustion phasing and controllability was evaluated.
In case ofn-butanol HCCI mode from low to medium engine loads ultralowsoot and NOx emissions were observed without use of EGR.However, in case of diesel HCCI it depends on high levels of dilution. Under thesecondition boost was not having much influence on emissions. Furtherbased on trade-off between thermal efficiency and combustioninstability decides levels of boost required. Inaddition to this ITE was 43-46% which is comparable to dieselcombustion this was because lower reactivity of n-butanol resultsin optimal combustion phasing. With n-butanol as loadincreases peak pressure rise rate increases and it limits theload.
So EGR and boost is required to limit the peak pressure riserate and adjust the combustion phasing for better thermal efficiency. Withbutanol HCCI load range was extended upto 10 barIMEP, which is 25% higher than which can be achievedwith diesel with higher performance and ultra-low NOx and smokeemission.Inanother study, Yanai et al. (2015) used the same research enginein the above study in butanol-PFI and butanol-DI(injection pressure 90 MPa) mode at a constant speed of1500 rpm.
They have studied influence of injection timing, intake boost and EGRon engine performance, combustionand emission. Butanol-DI require low amount of EGR ascompared to butanol-PFI in order to control rate of pressure rise (ROPR). In caseof butanol-DI can be easily be controlled by delaying injectiontiming of butanol. Both butanol-PFI and DI resulted insimultaneous reduction in soot and NOx emission. However butanol-DI resultedin a little higher NOx as compared to butanol-PFI. For sameNOx and ROPR butanol-PFI resulted in lower ITE as comparedto butanol-DI because of improper combustion phasing.In both cases HC and CO emissions were high as compared to diesel engine. It is seenfrom literature n-butanol can be used as a sole fuel in CI engine butit need some modification in engineside as well as fuel side.
However,it can be used from low to medium load. This is because as load increases rateof pressure rise rate also increases and it restrictload that can be achieved. Very highamount of EGR is required to extend load.