Fuel Conversion Efficiency Research Articles

An assessment of fuel consumption and emissions from a diesel power generator converted to operate with ethanol

This work presents an analysis of a diesel power generator converted to operate in Otto cycle using ethanol as fuel. This conversion was done without changing the compression ratio of 17:1, with the build-up of adequate control for intake air mass flow rate, fuel injection, and ignition timing when operating with ethanol. The new conversion approach allows for simplicity of reversion to the original configuration. In Diesel cycle, the engine was fuelled with diesel oil containing 7% biodiesel injected directly into the combustion chamber. The in-cylinder pressure, emissions of carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOX), unburned hydrocarbons (THC), as well as fuel conversion efficiency, when operating with pure hydrous ethanol, were evaluated. The results showed no significant changes on THC emissions in Otto cycle configuration, in comparison with engine operation in Diesel cycle configuration. The emissions of CO2, CO, and NOX were increased when operating in Otto cycle with ethanol.

Promoting Effect of Tin on Binder‐Free CoSnx‐B/Ni‐foam Catalysts for Fuel Conversion Efficiency in Direct Borohydride Fuel Cell

AbstractThe anodic activity of anodic catalyst for borohydride oxidation reaction (BOR) and inhibiting the borohydride hydrolysis reaction (BHR) are crucial to development for direct borohydride fuel cells (DBFC). In this paper, binder free CoSnx‐B/Ni‐foam (x = 0, 0.33, 0.5, 1) anode catalysts for BOR were prepared by chemical reduction method. It is found that the tin (Sn) is favor for improving the catalytic activity of cobalt (Co) for BOR, meanwhile, the catalytic activity is in relation to Co/Sn atom ratios. A maximum power density of 158 mW cm−2 of DBFC anodic catalytic is achieved at 293 K using CoSn0.33‐B/Ni‐foam which is 1.58 times that of Co‐B/Ni‐foam (100 mW cm−2). The constant discharge test of DBFCs showed that the specific capacity or fuel conversion efficiency decrease with the catalytic activity increasing. However, for the same electrocatalyst, the fuel conversion efficiency increased with the discharge current grown, indicating that there is a BHR which was independent of electrocatalyst in the discharge process. The results showed that CoSnx‐B/Ni‐foam had superior activity for BOR, suggesting their potential application as anodes in DBFC.

Energy flow of a 2018 FIA F1 racing car and proposed changes to the powertrain rules

AbstractIn the last few years, the different teams have dramatically improved the directly injected, electrically assisted turbocharged, internal combustion engine of FIA F1 hybrid electric cars. With limited fuel flow rate, but unlimited boost, the engine is now delivering peak power at fuel conversion efficiencies about 45% running lean stratified with the help of some sort of jet ignition. The paper analyses the energy flow of a FIA F1 hybrid electric car covering one lap of the Monte Carlo race track of length 3.370 km. The amount of energy recovered is minimal, at the most 2 of the 9.77 MJ of braking energy, or 20.6%. The fuel consumption per lap, 1.16 kg of fuel, or 50.34 MJ of fuel energy, needed to deliver the 16.28-18.28 MJ of propulsive energy, at an outstanding average efficiency of 32 to 36%, may still be dramatically reduced. New rules are thus proposed to promote the development of technical features that could be beneficial to passenger car applications, from advanced turbo-compounding, to enhanced thermal and mechanical energy recovery, and better hybridization.

A comparative study of the effect of compression ratio on the efficiency and flame development angle in a Cooperative Fuel Research engine fueled with binary gasoline–alcohol blends

In the last few years, increasing concern about the harmful effects of the use of fossil fuels in internal combustion engines has been observed. In addition, the limited availability of crude oil has driven the interest in alternative fuels, especially biofuels. In the context of spark ignition engines, bioalcohols are of great interest owing to their similarities and blend capacities with gasoline. Methanol and ethanol have been widely used, mainly due to their knocking resistance. Another alcohol of great interest is butanol, thanks to its potential of being produced as biofuel and its heat value closer to gasoline. In this study, a comparative study of gasoline–alcohol blend combustion, with up to 20% volume, with neat gasoline has been carried out. A single-cylinder, variable compression ratio, Cooperative Fuel Research-type spark ignition engine has been employed. The comparison is made in terms of fuel conversion efficiency and flame development angle. Relevant information related to the impact in the combustion process of the use of the three main alcohols used in blends with gasoline has been obtained.

The Control Space for Knock Mitigation in Two-Stroke Engines for 10–25 kg Remotely Piloted Aircraft

Interest is growing in converting commercially available, two-stroke spark-ignition engines from motor gasoline to low-anti-knock-index fuel such as diesel and Jet A, where knock-limited operation is a significant consideration. Previous efforts have examined the knock limits for small two-stroke engines and explored the effect of engine controls such as equivalence ratio, combustion phasing, and cooling on engine operation during knock-free operation on high octane number fuel. This work culminates the research begun in those efforts, investigating the degree of knock-mitigation achievable through varying equivalence ratio, combustion phasing, and engine cooling on three small (28, 55, and 85 cm3 displacement) commercially available two-stroke spark-ignition engines operating on a 20 octane number blend of iso-octane and n-heptane. Combustion phasing had the largest effect; a 10 deg retardation in the CA50 mass-fraction burned angle permitted an increase in throttle that yielded a 9–11% increase in power. Leaning the equivalence ratio from 1.05 to 0.8 resulted in a 10% increase in power; enriching the mixture from 1.05 to 1.35 yielded a 6–7% increase in power but at the cost of a 25% decrease in fuel-conversion efficiency. Varying the flow rate of cooling air over the engines had a minimal effect. The results indicate that the addition of aftermarket variable spark timing and electronic fuel-injection systems offer substantial advantages for converting small, commercially available two-stroke engines to run on low-anti-knock-index fuels.

Computationally efficient prediction of cycle-to-cycle variations in spark-ignition engines

Cycle-to-cycle variations are important to consider in the development of spark-ignition engines to further increase fuel conversion efficiency. Direct numerical simulation and large eddy simulation can predict the stochastics of flows and therefore cycle-to-cycle variations. However, the computational costs are too high for engineering purposes if detailed chemistry is applied. Detailed chemistry can predict the fuels’ tendency to auto-ignite for different octane ratings as well as locally changing thermodynamic and chemical conditions which is a prerequisite for the analysis of knocking combustion. In this work, the joint use of unsteady Reynolds-averaged Navier–Stokes simulations for the analysis of the average engine cycle and the spark-ignition stochastic reactor model for the analysis of cycle-to-cycle variations is proposed. Thanks to the stochastic approach for the modeling of mixing and heat transfer, the spark-ignition stochastic reactor model can mimic the randomness of turbulent flows that is missing in the Reynolds-averaged Navier–Stokes modeling framework. The capability to predict cycle-to-cycle variations by the spark-ignition stochastic reactor model is extended by imposing two probability density functions. The probability density function for the scalar mixing time constant introduces a variation in the turbulent mixing time that is extracted from the unsteady Reynolds-averaged Navier–Stokes simulations and leads to variations in the overall mixing process. The probability density function for the inflammation time accounts for the delay or advancement of the early flame development. The combination of unsteady Reynolds-averaged Navier–Stokes and spark-ignition stochastic reactor model enables one to predict cycle-to-cycle variations using detailed chemistry in a fraction of computational time needed for a single large eddy simulation cycle.

Combustion, performance and emission analysis of a natural gas-hydrous ethanol dual-fuel spark ignition engine with internal exhaust gas recirculation

This manuscript presents a deep analysis of natural gas-hydrous ethanol dual-fuel combustion in a spark ignition engine with a modified compression ratio and an advanced intake valve opening strategy to promote internal exhaust gas recirculation (iEGR). Both fuels were port-fuel injected and two different liquid fuel replacements by compressed natural gas (CNG) were tested (18 and 45% by energy). Combustion, performance and pollutant emissions were investigated under stoichiometric air-fuel conditions at 4 bar of net indicated mean effective pressure (IMEP) and 1800 rpm. Results show that dual-fuel mode improves fuel conversion efficiency when compared to CNG-only operation, due to lower carbon monoxide (CO) and unburnt hydrocarbons (HCs) emissions as well as to a better combustion phasing. The use of iEGR, despite deteriorating the combustion process as expected (ignition delay, combustion duration and combustion stability), improves efficiency because of a decrease in pumping losses and wall heat transfer, as well as pollutant emissions reduction. Nitrogen oxide (NOx) emissions increase with dual-fuel operation. However, the influence of iEGR was found to be more significant under dual-fuel mode than under single-fuel operation, with NOx reductions of up to 70% and fuel conversion efficiency improvements of around 2.5%.

Effect of Ignition Timing and Hydrogen Fraction in Natural Gas Blend on Performance and Exhaust Emissions in a DI Engine

The aim of the study was to investigate the effect of ignition timing and hydrogen fraction on the performance and exhaust emissions of an engine. The engine was converted from port injection system to direct injection with enrichment hydrogen to natural gas at WOT condition and engine operation at 4000 rpm. The results showed that when hydrogen volume fraction was raised from 0 up to 50% at 20 bar injection pressure and at the ignition timing from 19 to 28 °CA BTDC, a good stratified effect was achieved. Also, performance results demonstrated that fuel conversion efficiency, power output, and torque were increased up to 3.7% and the brake thermal efficiency first rose and then fell with an increment of hydrogen enrichment to CNG. The peak cylinder pressure and temperature with the advance of ignition timing increased. In addition, the advance of the ignition timing caused NOx, HC, and CO emissions to decrease but with the increase in hydrogen fraction in the blend of fuel, HC, and CO dropped and NOx emission rose. This study concluded that the 30% blends of hydrogen and 21° BTDC ignition timing can optimize engine performance and emission without any engine modification.

Variable valve actuation–based combustion control strategies for efficiency improvement and emissions control in a heavy-duty diesel engine

High nitrogen oxide levels of the conventional diesel engine combustion often requires the introduction of exhaust gas recirculation at high engine loads. This can adversely affect the smoke emissions and fuel conversion efficiency associated with a reduction of the in-cylinder air-fuel ratio (lambda). In addition, low exhaust gas temperatures at low engine loads reduce the effectiveness of aftertreatment systems necessary to meet stringent emissions regulations. These are some of the main issues encountered by current heady-duty diesel engines. In this work, variable valve actuation–based advanced combustion control strategies have been researched as means of improving upon the engine exhaust temperature, emissions, and efficiency. Experimental analysis was carried out on a single-cylinder heady-duty diesel engine equipped with a high-pressure common-rail fuel injection system, a high-pressure loop cooled exhaust gas recirculation, and a variable valve actuation system. The variable valve actuation system enables a late intake valve closing and a second intake valve opening during the exhaust stroke. The results showed that Miller cycle was an effective technology for exhaust temperature management of low engine load operations, increasing the exhaust gas temperature by 40 °C and 75 °C when running engine at 2.2 and 6 bar net indicated mean effective pressure, respectively. However, Miller cycle adversely effected carbon monoxide and unburned hydrocarbon emissions at a light load of 2.2 bar indicated mean effective pressure. This could be overcome when combining Miller cycle with a second intake valve opening strategy due to the formation of a relatively hotter in-cylinder charge induced by the presence of internal exhaust gas recirculation. This strategy also led to a significant reduction in soot emissions by 82% when compared with the baseline engine operation. Alternatively, the use of external exhaust gas recirculation and post injection on a Miller cycle operation decreased high nitrogen oxide emissions by 67% at a part load of 6 bar indicated mean effective pressure. This contributed to a reduction of 2.2% in the total fluid consumption, which takes into account the urea consumption in aftertreatment system. At a high engine load of 17 bar indicated mean effective pressure, a highly boosted Miller cycle strategy with exhaust gas recirculation increased the fuel conversion efficiency by 1.5% while reducing the total fluid consumption by 5.4%. The overall results demonstrated that advanced variable valve actuation–based combustion control strategies can control the exhaust gas temperature and engine-out emissions at low engine loads as well as improve upon the fuel conversion efficiency and total fluid consumption at high engine loads, potentially reducing the engine operational costs.

Experimental Investigation of Fuel Anti-Knock-Index Requirements in Three Small Two-Stroke Engines for Remotely Piloted Aircraft

Small remotely piloted aircraft (10–25 kg) that are powered by internal combustion engines typically operate on gasoline with an anti-knock index (AKI) > 80. To comply with the single-battlefield-fuel initiative [Department of Defense (DoD) Directive 4140.25], interest has increased in converting power plants for these platforms to run on low-AKI fuels such as diesel and Jet-A with AKIs of ∼20. It has been speculated that the higher losses (short circuiting, incomplete combustion, heat transfer) that cause these engines to have lower efficiencies than their conventional-scale counterparts may also relax their required fuel AKI. The fuel-AKI requirements of three two-stroke spark ignition (SI) engines with 28, 55, and 85 cm3 displacements were mapped, and the performance was compared to that on 98 ON (octane number) fuel. Switching from 98 ON fuel to 20 ON (Jet-A and diesel equivalent AKI) fuel while maintaining optimum combustion phasing led to a 3–5 crank-angle degree (CAD) reduction in burn angle, a 2–3% increase in power, and a 0.5–1% (absolute) increase in fuel-conversion efficiency at non-knock-limited conditions through shortening of the CA0–CA10 burn angle. The efficiency improvement translates to a 6% increase in range or endurance. The results indicate that abnormal combustion is not a significant obstacle to operating small commercial-off-the-shelf (COTS) engines on low-AKI fuels and that most of the power and efficiency improvements demonstrated in previous heavy-fuel conversion efforts were the result of modifications made to accommodate low-volatility fuels, not the faster burn rate of the low-AKI fuels themselves.

An experimental investigation of the performance and emissions of a hydrogen-diesel dual fuel compression ignition internal combustion engine

The present research study the emissions, the engine performance, and the maximum substitution of diesel by hydrogen in a turbocharged four-cylinder direct injection diesel engine. Moreover, the relationship between the hydrogen flammability limit, engine knock and hydrogen energy substitution was explored. Measurements were done at three engine loads (30%, 60%, 100%) while maintaining constant the engine speed (2400 rpm) whereas the engine knock was detected through an in-house non-invasive system. According to the experimental measurements, backfire took place at hydrogen concentration higher than the downward flammability limit. The maximum hydrogen energy substitutions were 80%, 60%, and 40% corresponding to engine loads of 30%, 60%, and 100%, respectively. The maximum reduction of diesel consumption was 54.2% with respect to 100% diesel operation at 30% of engine load and 80% of hydrogen energy substitution. Brake fuel conversion efficiency decreased as hydrogen addition increased for all the engine loads tested. This decrease may be mainly caused by the steam formation during the hydrogen combustion. Brake specific CO2 carbon dioxide emissions were reduced in most cases whereas the effect on brake specific NO emissions was dependent on engine load. At low engine load, a reduction in NO emissions was observed as hydrogen addition increased. Opacity was reduced in all cases and demonstrated the instability of operation near to the backfire region at 100% of engine load.

Performance and emission assessment of a multi-cylinder S.I engine using CNG & HCNG as fuels

The present study was carried out to assess the possibility of using the HCNG in the commercially available CNG vehicles, as the available literature indicated the benefits of adding hydrogen to CNG in small percentages by volume, leading to improved combustion characteristics of CNG and yielding sizeable benefits, regarding improved engine performance and reduced engine emissions in automotive applications. In the present study, a commercially available CNG manifold carburation kit, commonly known as “sequential injection” in the market, is evaluated for its operation characteristics, on a Spark Ignited (SI), MPFI automotive engine, of a mass-produced passenger vehicle, converted for gas operation, using, gasoline, CNG, HCNG 10% and HCNG 18% as fuels. In the study, the following performance parameters, torque, power, thermal efficiency, brake specific energy consumption (BSEC), lambda, engine oil temperature, exhaust gas species were measured. After exhaustive engine testing, a comparison of engine performance emission characteristics for gasoline, CNG and HCNG 10% and HCNG 18% is presented. The engine performance using the optimized MAP tables demonstrated torque and power improvements for HCNG 10% and HCNG 18% in comparison to CNG. The torque benefits up-to 6% and power benefits up-to 4% were observed. The fuel energy consumption was measured to be reduced, and improvement in fuel conversion efficiency was also observed. Hydrogen substitution in CNG helped in reducing CO, HC, CO2 emissions for HCNG in comparison to CNG. Increase in NOx emission was observed for HCNG in comparison with CNG. Superior engine emission characteristics in comparison to gasoline and CNG is also demonstrated. The commercially available sequential gas manifold carburation was found to be suitable for HCNG 10% and HCNG 18%.

Investigation and Optimization of Cam Actuation of an Over-Expanded Atkinson Cycle Spark-Ignited Engine

<div class="section abstract"><div class="htmlview paragraph">An over-expanded spark ignited engine was investigated in this work via engine simulation with a design constrained, mechanically actuated Atkinson cycle mechanism. A conventional 4-stroke spark-ignited turbo-charged engine with a compression ratio of 9.2 and peak brake mean effective pressure of 22 bar was selected for the baseline engine. With geometry and design constraints including bore, stroke, compression ratio, clearance volume at top dead center (TDC) firing, and packaging, one over-expanded engine mechanism with over expansion ratio (OER) of 1.5 was designed. Starting with a validated 1D engine simulation model which included calibration of the in-cylinder heat transfer model and SI turbulent combustion model, investigations of the Atkinson engine including cam optimization was studied. The engine simulation study included the effects of offset of piston TDC locations as well as different durations of the 4-strokes due to the mechanism design. Incremental effects of adjusted combustion phasing, scaled valve durations, to a fully optimized cam duration and phasing are determined, and the impacts of each discussed. A constant speed load sweep was conducted to compare the net indicated fuel conversion efficiency difference between baseline and Atkinson cycle engine. Besides, two speed load conditions (1300rpm, 3.3bar IMEPnet and 1750rpm and 10.3bar IMEPnet) with valve timing optimization were also investigated.</div><div class="htmlview paragraph">Results from the study indicate that with an increase in the load from 4bar to 12bar IMEPnet at 2500rpm, over expansion contributed to an increase of 2.3% in net indicated efficiency. Furthermore, with valve optimization, negative work was avoided in the Atkinson cycle engine at 3.3bar IMEPnet, 1300rpm with an increase of 2% in the net indicated fuel conversion efficiency. At 10.3bar IMEPnet and 1750rpm, net indicated fuel conversion efficiency increased by 4.6%.</div></div>

A case study on combined cycle power plant integrated with solar energy in Trinidad and Tobago

Aim of the paper is to evaluate the benefit of a renewable energy initiative for Trinidad and Tobago. Trinidad and Tobago have abundant natural gas, a highly developed power generation system almost entirely based on combustion fuels, high solar irradiation, but skies often covered by clouds, a detrimental factor for concentrated solar power technologies. The simple, consolidated, parabolic trough technology, without the addition of thermal energy storage, has the potential to deliver better than solar photovoltaic capacity factors at a comparable cost when mass produced. Integration with natural gas combustion may permit to address the issues of clouds coverage. A computational analysis is proposed for an Integrated Solar Combined Cycle power plant comprising a reference combined cycle gas turbine plant, and a small solar field, located in Trinidad and Tobago. The simulations demonstrate the advantages, in terms of fuel conversion efficiency, of the small solar field addition. On average over the year, the plant operates over the morning and afternoon periods, of length about 8 h a day, at an efficiency of 57.34%, about 2.58% better, and over the mid-day periods, of length about 4 h a day, at an efficiency of 57.97%, about 3.16% better.

Effects of mixture enleanment in combustion and emission parameters using a flex-fuel engine with ethanol and gasoline

The growing global energy demand, the fossil fuel depletion and increasing CO2 and pollutant emissions in arising from human activities are increasingly impacting the economy and government measures. For this reason, the automotive industry is constantly in search for new and environment friendly technologies and strategies, such as the use of biofuels and the variation in air-fuel ratio. These strategies have already been vastly studied, but few studies were conducted with ethanol. Thereby, this paper aims to analyze and compare the effects of ethanol and gasoline mixture enleanment in a flex-fuel engine in terms of performance, emissions and combustion. For this, it was evaluated how indicated specific fuel consumption (ISFC), emissions and combustion patterns are affected when using both Brazilian commercial gasoline (E27) and hydrous ethanol (E96) in lean conditions. The results show similar combustion parameter behavior for both fuels, pointing to ISFC reduction when operating in lean combustion modes of more than 5% and 12% for ethanol and gasoline, respectively. Despite the lower thermal and fuel conversion efficiencies resulting from the smaller Lower Heating Value (LHV), the advantage of the biofuel appears in the emission analysis. For both fuels, lean combustion results in virtual elimination of carbon monoxide (CO) emission, decreasing of 89% in nitrogen oxides (NOx) for ethanol and 74% for gasoline. Added to this, ethanol’s combustion results in lower HC emission, highlighting the potential of this biofuel.

Development of a homogeneous charge pre-chamber torch ignition system for an SI engine fuelled with hydrous ethanol

Energy is the key to wellbeing and sustainability of modern civilization and its demand continues to increase. With the end of oil availability perspectives and the world energy crisis, technological solutions are needed from the scientific community to promote the reduction of fossil fuel consumption, the maximization of fuel conversion efficiency and the reduction of emission levels in internal combustion engines. Aiming at reaching these needs, the use of a pre-chamber ignition system in spark-ignition (SI) engines is a potential alternative enabling such engines to operate with lean mixtures and with a wide variety of fuels. In this study, a methodology was developed to design and characterize experimentally a homogeneous charge pre-chamber torch ignition system fuelled with hydrous ethanol (with 6–7% in mass of water content) and using lean burn mixtures (excess air ratio (λ) > 1.0). The methodology, which has not been reported previously in other works, consisted of a one-dimensional mathematical model, that allowed for the definition of pre-chamber geometrical parameters. The device was manufactured and adapted to an SI engine, requiring no additional work to the cylinder head, as the pre-chamber was mounted in the original spark-plug screw thread. The prototype was experimentally characterized on an active dynamometer, and performance, combustion, emission and combustion visualization were studied. The pre-chamber ignition engine expanded the flammability limit in comparison with the baseline engine. For λ = 1.4, engine fuel conversion efficiency was increased by 5.4%, specific fuel consumption decreased by 22% and nitrogen oxides (NOx) emissions reduced by 52%, but total hydrocarbons (THC) emissions increased. Improvements achieved were due to the faster burn rates characterized by the reduced MBF 0–10%, combustion duration and combustion instability, and also the increased thermodynamic efficiency and the lower combustion temperatures achieved with lean burn technology. From the conclusions obtained in this research, the homogeneous pre-chamber torch ignition system developed for hydrous ethanol has potential for application and marketability integration, as an alternative technology able to help meet energy demands in a sustainable manner.

Design of Direct Injection Jet Ignition High Performance Naturally Aspirated Motorcycle Engines

Thanks to the adoption of high pressure, direct injection and jet ignition, plus electrically assisted turbo-compounding, the fuel conversion efficiency of Fédération Internationale de l'Automobile (FIA) F1 engines has been spectacularly improved up to values above 46% peak power, and 50% peak efficiency, by running lean of stoichiometry stratified in a high boost, high compression ratio environment. Opposite, Federation Internationale de Motocyclisme (FIM) Moto-GP engines are still naturally aspirated, port injected, spark ignited, working with homogeneous mixtures. This old fashioned but highly optimized design is responsible for relatively low fuel conversion efficiencies, and yet delivers an outstanding specific power density of 200 kW/liter. The potential to improve the fuel conversion efficiency of Moto-GP engines through the adoption of direct injection and jet ignition, prevented by the current rules, is herein discussed based on simulations. As two-stroke engines may benefit from direct injection and jet ignition more than four-stroke engines, the opportunity of a return of two-stroke engines is also argued, similarly based on simulations. About the same power, but at a better fuel efficiency, of today’s 1000 cm3 four stroke engines, may be obtained with lean stratified direct injection jet ignition engines, four-stroke of 1450 cm3, or two-stroke of 1050 cm3. About the same power and fuel efficiency may also be delivered with stoichiometric engines direct injection jet ignition two-stroke of 750 cm3.

Effects of EGR and combustion phasing on the combustion and emission characteristic of direct-injection CI engine fueled with n-butanol/diesel blends

Shortage of fossil fuel and stringent emission regulations require less pollutant emissions and better fuel conversion efficiency from modern internal combustion (IC) engines. Butanol is of particular interest as a renewable biofuel for advanced compression ignition (CI) engines, which has been receiving widely researches consequently. In order to more comprehensively evaluate the application of butanol on modern CI engine, exploration strategy was focused on the combining of EGR and combustion phasing control to achieve ultra-low NOx and smoke emission without penalty on fuel economy. Experiment was conducted under constant engine speed and both the high and low engine load conditions with three volume fractions of butanol up to 30%. Results indicate that butanol blending causes extended ignition delay, increased premixed combustion ratio (PCR) and retarded combustion phasing, which is more significant at low load condition. Butanol/diesel blends can dramatically reduce exhaust smoke and particle emissions without increasing NOx emissions at, however, the expense of lower thermal efficiency than that of pure diesel. Reduced thermal efficiency can be recovered by properly matching EGR and combustion phasing under a low level of overall emission.

Influence of fuel bio-alcohol content on the performance of a turbo-charged, PFI, spark-ignition engine

In this work, the behavior of an engine running with binary and ternary mixtures of n-butanol, ethanol and gasoline has been investigated.Analyses have been performed at different engine speed both at low load and at high load. For each blend, the air to fuel ratio has been kept stoichiometric, while the spark time has been tuned in order to maximize the engine brake torque and hence the engine fuel conversion efficiency. The performance, the combustion characteristics and the pollutant emissions of the engine fueled by biofuel mixtures have been compared to those characterizing the engine running with neat gasoline.In an attempt to provide a guideline for the development of engines running with every mix of gasoline and alcohol, measurements are presented as a function of the oxygen content of the fuel. When the fuel oxygen content increases, results show that the optimal spark time must be retarded at part load while must be advanced at high load. At this operation, the maximum obtainable efficiency increases, the CO2 specific emissions decrease almost linearly together with NOx and HC specific emissions, the engine torque remains practically the same, while the brake specific fuel consumption increases.

Experimental investigation on combustion characteristics in dual-fuel dual-injection engine

Dual-injection strategy combined with dual-fuel can provide flexible and instantaneous blend ratios according to engine demands under different operating conditions. Furthermore, ethanol direct injection has the potentials to increase the engine compression ratio and thermal efficiency by taking advantages of ethanol fuel such as the high octane number and latent heat. Therefore, in order to maximize the charge cooling effect, a dual-fuel (gasoline and ethanol) dual-direct injection system is proposed and investigated in this paper. In current work, different injection modes in terms of knock suppression and combustion performance are compared and studied on a single-cylinder SI engine with stoichiometric air/fuel ratios. The results show that the new injection strategy of dual-fuel dual-direct injection mode can significantly expand engine load compared with conventional modes of gasoline direct injection plus ethanol port injection and ethanol direct injection plus gasoline port injection. Direct injection ethanol mode can reduce knocking tendency. However, with higher brake mean effective pressure, dual-fuel dual-injection mode shows higher knock tendency. Dual-fuel dual-injection mode can increase brake mean effective pressure and thermal efficiency simultaneously. However, the brake thermal efficiency behavior is non-linear when increasing brake mean effective pressure and direct injection ethanol mass fraction. The equivalent heat value brake specific fuel consumption decreases with the increase of direct injection ethanol ratio, and dual-fuel dual-injection mode has superior fuel conversion efficiency. Relatively high maximum pressure can be found in dual-fuel dual-injection mode. With the increase of ethanol ratio, the combustion phasing is further advanced, resulting in better combustion, which contributes to higher thermal efficiency.