Neat N-butanol Research Articles

Auto-ignition and detonation of n-butanol and toluene reference fuel blends (TRF)

The primary purpose of the paper is to report a study of the auto-ignitive and anti-knock properties, firstly of neat n-butanol in air, and secondly of its blends with a gasoline-type, Toluene Reference Fuel (TRF). This involved blending ratios of 10, 20, 40, and 85% of n-butanol by volume with a TRF. Pressures were in the range 2–6 MPa, and temperatures ranged from 678 to 916 K. Mathematical modelling of the detailed chemical kinetics for these conditions, using the CANTERA code, yielded values of the duration of the main heat release rate, and revealed the main reactions influencing them. High knock intensities were not anticipated, but checks were made of whether operational points lay within the Detonation Peninsula. This peninsula is constructed by plotting values of ξ, the ratio of acoustic to auto-ignitive velocity, against ɛ, the ratio of the transit time of an acoustic wave through a hot spot, to the heat release time (τe).At 2 MPa and 702–855 K, the addition of n-butanol to the TRF moved these coordinates away from the peninsula towards the deflagrative regime. At blend ratios of 85%, n-butanol mixtures and pure n-butanol were found to lie close to the compression curve for methane, known to have good anti-knock properties. This suggests that the addition of n-butanol to gasoline would improve knock resistance at this operating condition. However, at 6 MPa and 916 K, the addition of n-butanol had the opposite effect, reducing the anti-knock resistance of the blend and pushing it deeper into the peninsula. Uncertainties and limitations of the ξ/ɛ methodology are also discussed.

Fuel Stratification and Partially Premixed Combustion With Neat n-Butanol in a Compression Ignition Engine

Homogeneous charge compression ignition (HCCI) has been considered as an ideal combustion mode for compression ignition (CI) engines due to its superb thermal efficiency and low emissions of nitrogen oxides (NOx) and particulate matter. However, a challenge that limits practical applications of HCCI is the lack of control over the combustion rate. Fuel stratification and partially premixed combustion (PPC) have considerably improved the control over the heat release profile with modulations of the ratio between premixed fuel and directly injected fuel, as well as injection timing for ignition initiation. It leverages the advantages of both conventional direct injection compression ignition and HCCI. In this study, neat n-butanol is employed to generate the fuel stratification and PPC in a single cylinder CI engine. A fuel such as n-butanol can provide additional benefits of even lower emissions and can potentially lead to a reduced carbon footprint and improved energy security if produced appropriately from biomass sources. Intake port fuel injection (PFI) of neat n-butanol is used for the delivery of the premixed fuel, while the direct injection (DI) of neat n-butanol is applied to generate the fuel stratification. Effects of PFI-DI fuel ratio, DI timing, and intake pressure on the combustion are studied in detail. Different conditions are identified at which clean and efficient combustion can be achieved at a baseline load of 6 bar IMEP. An extended load of 14 bar IMEP is demonstrated using stratified combustion with combustion phasing control.

Investigation of ignition characteristics and performance of a neat n-butanol direct injection compression ignition engine at low load

Neat (100%) n-butanol was implemented in a direct injection (DI) compression ignition (CI) engine. The ignition, combustion, and emission characteristics at low engine load (below 6.5bar IMEP), including near idling, were investigated. The engine experiments were performed using a modern common rail type single cylinder DI CI engine with a compression ratio of 18.2:1. Chemical kinetic simulations were also conducted to analyze the ignition characteristics of the experiments. The research results showed that neat n-butanol could not be auto-ignited at normal intake temperature and pressure conditions due to its low reactivity. However, the use of a high intake pressure of 0.75bar gauge, and an injection timing of −26° ATDC at 5.0bar IMEP, enabled auto-ignition even without the use of intake heating. One possible reason for this was attributed to the enhancement of the low temperature reaction regime. The ignition timing advancement sensitivity to intake pressure was approximately 1.0°CA/0.1bar at 5.0bar IMEP, and a higher intake pressure allowed a wider injection timing range. A neat n-butanol fueled DI CI engine had a five times longer ignition delay and a 85% longer combustion duration than the same engine fueled with diesel at 2.0bar IMEP. However, the combustion duration tended to shorten rapidly with increasing engine load, which was the opposite tendency to diesel. At low load, the nitrogen oxides (NOx) and soot emissions were very low compared to those of diesel, whereas the total hydrocarbons (THC), formaldehyde (HCHO), and carbon monoxide (CO) were higher than those of diesel. Carbon dioxide (CO2) emission was lower than that of diesel. This could be due to the reduced CO oxidation and the lower carbon content in n-butanol. Finally, by combining the previously published results with these results in this research, fuel injection strategies and intake oxygen conditions required to achieve low NOx (≤0.60g/kWh) and soot (≤0.02g/kWh) emissions and moderated maximum cylinder pressure rise rate (≤10bar/°CA) were summarized over a wide load range of 2.0–11.5bar IMEP.

Clean combustion of n-butanol as a next generation biofuel for diesel engines

This work investigates the applicability of n-butanol as a next generation biofuel to replace diesel in compression ignition engines for efficient operation, pollutant mitigation, and CO2 reduction. A high compression ratio (18.2:1) diesel research engine is configured to run on neat n-butanol. Due to the fuel property departure from diesel, n-butanol combustion exhibits striking combustion characteristics. Alternative combustion strategies, including via partially premixed compression ignition and homogeneous charge compression ignition, are enabled efficiently owing to distinctive fuel properties of n-butanol. The compression ignition of the (partially) premixed n-butanol and air mixture is capable of producing diesel-like engine efficiency and significant nitrogen oxide and smoke reductions. As the engine load increases, however, such neat n-butanol combustion exhibits rapid burning and suffers abrupt pressure rise. Thereby the engine load is generally limited below 50% of the baseline capability. A split-combustion strategy, which employs multiple event fuel injections, is found to be effective to modulate the noise of n-butanol clean combustion, thereby enabling neat n-butanol application across the full engine load range.

Fuel efficiency analysis and peak pressure rise rate improvement for neat n-butanol injection strategies

Engine tests were conducted to investigate the efficiency and the peak pressure rise rate performance of different fuel injection strategies for the direct injection of neat n-butanol in a compression ignition engine. Three different strategies were tested: a single-shot injection; a pilot injection; a post-injection. A single-shot injection timing sweep revealed that early injections had the highest indicated efficiency while late injections reduced the peak pressure rise rate at the cost of a slightly reduced thermal efficiency. Delayed single-shot injections also had increased emissions of nitrogen oxides, total hydrocarbon and carbon monoxide. Addition of a pilot injection had a negative effect on the peak pressure rise rate. Because of the low cetane number of butanol and the relatively lean and well-premixed air–fuel mixture, the pilot injection failed to autoignite and instead ignited simultaneously with the main injection. This resulted in slightly increased peak pressure rise rates and significantly increased unburned butanol hydrocarbon emissions. Conversely, the use of an early post-injection produced a noticeable engine power output and allowed the main injection to be shortened and the peak pressure rise rate to be substantially reduced. However, relatively early post-injections slightly reduced the indicated efficiency and increased the nitrogen oxide emissions and the carbon monoxide emissions compared with the single-shot injection strategy. These results recommended the use of a single-shot injection for low loads and medium loads owing to a superior thermal efficiency and suggested that the application of a post-injection may be more suited to high-load conditions because of the substantially reduced peak pressure rise rates.

Experimental investigation on the knocking combustion characteristics of n-butanol gasoline blends in a DISI engine

n-Butanol is a very competitive alternative biofuel for spark ignition (SI) engines given its many advantages. Current researches are mainly concentrated on the overall combustion and emissions performance concerning the feasibility of n-butanol gasoline blends in SI engines. In this work, focus was given on the knocking combustion characteristics of operation with pure n-butanol as well as a blend fuel with 20% volume content of n-butanol (Bu20), which was investigated experimentally in a direct-injection spark ignition (DISI) single cylinder engine. Operation condition is fixed at a constant engine speed of 1500r/min, using three throttle openings with stoichiometric air–fuel ratio. Spark timing was swept to achieve different knocking levels. The results of n-butanol and Bu20 were benchmarked against those obtained by the research octane number (RON) 92 commercial gasoline. Compared with the baseline fuel gasoline, neat n-butanol shows better anti-knock ability with more advanced knock limited spark timing, whereas slightly deteriorative knock resistance can be found for Bu20. It is hypothesized Bu20 has higher end gas temperature due to its higher brake mean effective pressure (BMEP) and faster burning rate compared with gasoline, which indicates the knock tendency depends not only on the fuel octane number, but also on the factors that affect the end gas thermodynamic state. The heavier knock propensity of Bu20 is furthermore confirmed by its more advanced knock onset and higher peak oscillation pressure. Results of fast fourier transform (FFT) indicate the knocking oscillation frequencies are mainly determined by the combustion chamber resonance modes. Statistics probability distribution and cumulative distribution are applied to evaluate the knock intensity variation for each fuel.

Investigation of Fuel Injection Strategies for Direct Injection of Neat n-Butanol in a Compression Ignition Engine

Investigation of Fuel Injection Strategies for Direct Injection of Neat n-Butanol in a Compression Ignition Engine

Numerical analysis of a downsized spark-ignition engine fueled by butanol/gasoline blends at part-load operation

In this paper, the performance of a turbocharged SI engine, firing with butanol/gasoline blends, has been investigated by means of numerical simulations of the engine behavior. When engine fueling is switched from gasoline to alcohol/gasoline mixture, engine control parameters must be adapted. The main necessary modifications in the Electronic Control Unit have been highlighted in the paper.Numerical analyses have been carried out at partial load operation and at two different engine speeds (3000 and 4000rpm). Several n-butanol/gasoline mixtures, differing for the alcohol contents, have been analyzed.Such engine performances as torque and indicated efficiency have been evaluated. Both these characteristics decrease with the alcohol contents within the mixtures. On the contrary, when the engine is fueled by neat n-butanol, torque and efficiency reach values about 2% higher than those obtained with neat gasoline.Furthermore, the optimal spark timing, for alcohol/gasoline mixture operation, must be retarded (up to 13%) in comparison with the correspondent values of the gasoline operation.In general, engine performance and operation undergo little variations when fuel supplying is switched from gasoline to alcohol/gasoline blends.

Postinjection Strategy for the Reduction of the Peak Pressure Rise Rate of Neat n-Butanol Combustion

Enhanced premixed combustion of neat butanol in a compression ignition engine can have challenges with regards to the peak pressure rise rate (PRR) and the peak in-cylinder pressure. It was proposed to utilize a butanol postinjection to reduce the peak PRR and the peak in-cylinder pressure while maintaining a constant engine load. Postinjection timing and duration sweeps were carried out with neat n-butanol in a compression ignition engine. The postinjection timing sweep results indicated that the use of an early butanol postinjection reduced the peak PRR and the peak in-cylinder pressure and it was observed that there was an optimal postinjection timing range for the maximum reduction of these parameters. The results also showed that an early postinjection of butanol increased the nitrogen oxide emissions, and a Fourier transform infrared spectroscopy (FTIR) analysis revealed that late postinjections increased the emissions of unburned butanol. The postinjection duration sweep indicated that the peak PRR was significantly reduced by increasing the postinjection duration at constant load conditions. There was also a reduction in the peak in-cylinder pressure. Measurements with a hydrogen mass spectrometer showed that there was an increased presence of hydrogen in the exhaust gas when the postinjection duration was increased but the total yield of hydrogen was relatively low. It was observed that the coefficient of variation for the indicated mean effective pressure was significantly increased and that the indicated thermal efficiency was reduced when the postinjection duration was increased. The results also showed that there were increased nitrogen oxide, carbon monoxide, and total hydrocarbon (THC) emissions for larger postinjections. Although the use of a postinjection resulted in emission and thermal efficiency penalties at medium load conditions, the results demonstrated that the postinjection strategy successfully reduced the peak PRR, and this characteristic can be potentially useful for higher load applications where the peak PRR is of greater concern.

Improved SI engine efficiency using Acetone–Butanol–Ethanol (ABE)

Alcohols, especially n-butanol, have received a lot of attention as potential fuels and have shown to be a possible alternative to pure gasoline. The main issue preventing butanol’s use in modern engines is its relatively high cost of production. ABE, the intermediate product in the ABE fermentation process for producing bio-butanol, is being studied as an alternative fuel because it not only preserves the advantages of oxygenated fuels, but also lowers the cost of fuel recovery for individual component during fermentation. With the development of advanced ABE fermentation technology, the volumetric percentage of acetone, butanol and ethanol in the bio-solvents can be precisely controlled. In this respect, it is desirable to estimate the performance of different ABE blends to determine the best blend and optimize the production process accordingly. In this paper, pure ABE fuels with different component volumetric ratio, (A:B:E of 3:6:1, 6:3:1 and 5:14:1), were combusted in a naturally aspirated, port-fuel injected spark ignited engine. The performance of these blends was evaluated through measurements of in-cylinder pressure, and various exhaust emissions. In addition, pure gasoline and neat n-butanol were also tested as baselines for comparison of ABE fuels. The tests were conducted at an engine speed of 1200RPM and loads of 3 and 5bar brake mean effective pressure (BMEP) under different equivalence ratios. On the basis of the experimental data, the combustion characteristics and emission behavior of these fuels have been presented and discussed. It was found that in terms of thermal efficiency, ABE(6:3:1) might be much better suited for use as an alternative fuel, relative to ABE(3:6:1) or n-butanol.

Impact of Fuelling Techniques on Neat n-Butanol Combustion and Emissions in a Compression Ignition Engine

Impact of Fuelling Techniques on Neat n-Butanol Combustion and Emissions in a Compression Ignition Engine

Evidence for Preferential Solvation in the Cyclohexane/n-Butanol Binary Solvent System

We report on the rotational diffusion and vibrational population relaxation dynamics of the polycyclic aromatic hydrocarbon (PAH) perylene in a series of cyclohexane/n-butanol binary solvent systems. The molecular scale heterogeneity of this binary system is seen in both types of data. The rotational diffusion results show that in neat n-butanol and neat cyclohexane perylene reorients as an oblate rotor, but for all binary solvent systems examined this chromophore reorients as a prolate rotor. The perylene ring breathing mode is nearly degenerate with the n-butanol terminal methyl group rocking mode and vibrational population relaxation data for the perylene ring breathing mode reveal a substantial decrease in the relaxation time constant with the addition of small amounts of n-butanol to cyclohexane. This finding, in concert with the rotational diffusion data, indicates that perylene is solvated preferentially by n-butanol in cyclohexane/n-butanol binary solvent systems. The implication of this finding is that the cyclohexane/n-butanol binary solvent mixture is not homogeneous on nanometer length scales.

Direct injection of neat n-butanol for enabling clean low temperature combustion in a modern diesel engine

This study investigates the effects of neat n-butanol replacing conventional diesel fuels to enable clean combustion on a modern common-rail diesel engine. Systematic engine experiments are conducted to examine the combustion characteristics and exhaust emissions in correlation to n-butanol’s relatively high oxygen content and high volatility but low ignitability, and control strategies are thereafter developed for enabling clean and efficient combustion of neat n-butanol. Compared to its diesel counterpart, the single-shot injection of neat n-butanol offers substantially reduced NOx emissions without the use of EGR and near-zero soot emissions, but the applicable injection timing window is narrower for n-butanol limited by high maximum rates of pressure rise and/or unstable combustion. EGR is effective to reduce the combustion roughness, but it further narrows the applicable injection timing window and deteriorates the HC and CO emissions. A control strategy that deploys multi-shot injections combined with moderate use of EGR is developed and applied to improve the combustion controllability and exhaust emissions while minimizing the penalties in the engine efficiency.

Preliminary Investigation of Direct Injection Neat n-Butanol in a Diesel Engine

The characteristics of combustion, emissions, and thermal efficiency of a diesel engine with direct injection (DI) neat n-butanol were investigated. The engine ran at a load of 6.5–8.0 bar indicated mean effective pressure (IMEP) at 1500 rpm engine speed and the injection pressure was controlled to 900 bar. The intake boost pressure, injection timing, and EGR rate were adjusted to investigate the engine performance. The tests demonstrated that neat n-butanol had the potential to achieve ultralow emissions. However, challenges related to reducing the pressure rise rate and improving the ignition controllability were identified.

Performance, combustion and emission characteristics of a spark-ignition engine with simultaneous injection of n-butanol and gasoline in comparison to blended butanol and gasoline

SUMMARY Simultaneous injection of n-butanol and gasoline through a new system of two injectors directing the sprays towards the back of the intake valve in a spark-ignition engine was tried in lieu of injecting a blend of these fuels through a single injector. This system avoids the problem of phase separation, which is generally faced during the use of alcohol-gasoline blends. Experiments were conducted on a spark-ignition engine with this dual injection system using a fuel ratio of 1:1 (B50S) on the mass basis. High-speed photographs indicated that the sprays from the injectors did not interfere till they reached the intake valve. Comparisons were made with pre-blended butanol-gasoline (B50) and neat (100%) gasoline at the best spark timing. All injection and spark parameters were controlled using a real time engine controller. Neat n-butanol (B100) was superior only near full throttle with improved efficiency of the engine of about 1.2% (absolute). Heat release rates were observed to be higher and more advanced with B100 at wide open throttle. However, a reverse of this trend was observed at the throttle position of 15%. NO emission was also lower by 30% with B100 at wide open throttle as compared with gasoline. However, a small increase in carbon monoxide (CO) levels was observed because of lower post combustion temperatures as compared with gasoline and B50S. Simultaneous injection reduced hydrocarbon (HC) emissions by 13% to 50% as compared with B50 (blended fuel). HC emissions with gasoline and B50S were similar. Nitric oxide (NO) emission was lower with B50S as compared with gasoline; however it was higher than B50 because of better combustion. On the whole, the developed dual injection system was superior to the conventional method of blending in terms of performance, emissions and ability to change the fuel ratio as needed. B50S is suitable at all throttle positions, whereas B100 shows benefits at full throttle conditions. Copyright © 2013 John Wiley & Sons, Ltd.

Experimental and modeling study of the auto-ignition of n-heptane/n-butanol mixtures

Ignition delay times of n-heptane/n-butanol mixtures (neat n-heptane, 80/20, 50/50, 20/80 and neat n-butanol in mole) diluted with argon were measured behind reflected shock waves. The experiments were performed in the temperature range of 1200–1500K, at pressures of 2 and 10atm and equivalence ratios of 0.5 and 1.0. Kinetic modeling was conducted for interpreting the oxidation of the fuel mixtures. The computed ignition delay times was then validated against the present measurements as well as the low-temperature data from literatures. It was found that the new blend model can give fairly good prediction on the ignition delay times. Particularly, it well captures the weakened negative-temperature-coefficient (NTC) behavior of the binary mixtures compared to neat n-heptane. Analysis on the effect of chemical structure of n-butanol shows that only a very limited part of n-butanol participates in the low-temperature branching due to the influence of OH group, leading to an increased ignition delay times at low temperature. The competition between n-heptane and n-butanol for OH radicals inhibits the consumption of n-heptane and promotes the consumption of n-butanol. Sensitivity analysis on ignition delay times was conducted and the dominant reactions in the oxidation of binary mixtures at high and low temperatures were identified respectively.