Stoichiometric Air-fuel Ratio Research Articles

A novel valve strategy for particulate matter reduction in a gasoline direct injection engine operated at cold conditions

In this study, we proposed a novel intake strategy to reduce Particulate matter (PM) emissions from gasoline direct-injection (GDI) engines during cold-start conditions emissions. This strategy is characterized by generating strong intake turbulence and low in-cylinder pressure during fuel injection through delayed intake valve opening, which theoretically promotes fuel atomization and fuel-air mixture, thereby suppressing PM formation during combustion. Experiments were conducted on a single-cylinder GDI research engine, operating at 1500 rpm, 3, 6, and 8 bar IMEP, and stoichiometric air-fuel ratio conditions with low coolant and lubricant temperatures to experimentally demonstrate the effectiveness of the proposed valve strategy in reducing PM emissions. Benchmark tests were performed using an intake camshaft with intake valve opening (IVO) at −13 °aTDC and intake valve closing (IVC) at 227 °aTDC. The novel strategy uses an intake camshaft with very late IVO at 66 °aTDC and IVC at 226 °aTDC. Two injection pressures (Pinj = 100/200 bar) were used to evaluate the pressure requirement for achieving low PM emissions with both strategies. Start of injection was swept and optimized to match the valve strategy. The results showed that the novel valve strategy leads to a 50%–90% reduction in particle number and mass emissions in cold-start conditions, and a lower injection pressure requirement to achieve comparable particle number and mass emissions compared with the normal one. For the novel valve strategy, the fuel impingement with early injection timings is largely mitigated, and thus an early injection timing shortly before the IVO is recommended.

Towards Understanding the Improvement in Stability for Fuels with Inhomogeneous Inlets

ABSTRACT This paper presents results from the Sydney inhomogeneous burner for two gaseous hydrocarbons: methane (CH4) and propane (C3H8). These different hydrocarbons enable the exploration of fuels with significantly different stoichiometric air-fuel ratios (A/F) and hence mixing requirements in the burner. Stability limits of blow-off velocities vs. fuel jet recession, identify that both fuels exhibit improvement due to inhomogeneity, albeit occurring at different equivalence ratios. For CH4, the largest improvement due to inhomogeneity, compared to the homogeneous limit, was close to φ = 4.76, which corresponds to V A /V F = 2. For C3H8, the peak stability occurred at φ = 12, which interestingly also corresponds to V A /V F = 2. Rayleigh imaging at 10 Hz, performed at the burner exit plane, was used to identify the mixing profiles of the two fuels for different equivalence ratios. It was verified that the optimal recess distance coincides with the most stoichiometric samples contacting the pilot, with the samples augmenting the pilot heat release. The addition of N2 further reduced the inhomogeneous improvement, verifying that mixing and the mixture near the pilot controls the inhomogeneous stability.

Experimental investigation of gasoline ethanol methanol iso-stoichiometric blends on SI engine

The current work presents the formulation and experimental investigation of E20 (Ethanol 20%, Gasoline 80% (v/v)) and its equivalent iso-stoichiometric GEM (Gasoline, Ethanol and Methanol) blends on performance and emission features of a single cylinder, four stroke SI engine. Experiments were carried out at constant engine load and at different engine speeds. The formulated blends were termed as binary blend E20 (G 80 E 20) and its equivalent GEM blends, E20_B1 (G 83 E 10 M 7), E20_B2 (G 85 E 5 M 10) and E20_B3 (G 87 E 0 M 13) respectively. The formulated E20 equivalent GEM blends have similar stoichiometric Air-Fuel ratio, Lower heating value and Octane number as binary E20 blend. The engine performance, emission values of blended fuels were measured and compared with pure gasoline, G. The results showed that the E20 equivalent GEM blends have similar brake thermal efficiency as the binary E20 blend and also improved compared to straight gasoline. And also exhaust emissions such as carbon monoxide (CO), unburned hydrocarbons (HC) show reduced values and increased nitrogen oxide (NOx) values for mixed fuels compared to pure gasoline.

Potential of ozone addition on dethrottling of a gasoline/ethanol blend-fueled direct injection spark ignition engine in part load

Several efforts are required to improve engine efficiency and decrease global carbon dioxide (CO2) emissions and local pollutant products. In countries like Brazil, with a four-decade long experience with ethanol, the use of fossil fuels, although widespread, is being put under intense scrutiny. Governmental programs like ROTA 2030 stimulate engine research and development focused on environment-friendly fuels such as bioethanol-gasoline blends. Brazilian gasoline has about a quarter of ethanol, reducing the carbon footprint while maintaining suitable energy density. Regardless of the fuel, the load control method in part load operation of spark ignition engine causes a considerable penalty in fuel conversion efficiency. For these reasons, ozone addition was tested as an ignition enhancer that would allow higher de-throttling to reduce part-load pumping losses. The residual gas was used to dilute the mixture due to the possibility of keeping the three-way catalyst working properly with the stoichiometric mixture. An experimental investigation on efficiency, emissions and combustion related parameters was carried out in a downsized 1.0 l turbocharged direct-injected engine. Experimental tests were performed at 3 bar of indicated mean effective pressure (IMEP), 1500 rpm and stoichiometric air-fuel ratio. Spark timing (ST) was adjusted to achieve maximum indicated efficiency and the fuel used was Brazilian gasoline. Different ozone concentrations were used as a mixture with the intake air to overcome unstable engine operation by enhancing ignition. The results showed that it is possible to increase the gas exchange efficiency with ozone addition by promoting de-throttling operation with residual gases. Furthermore, the ozone addition exhibits the potential to promote autoignition of the end gas with spark assistance, even with a low compression ratio and residual gas fraction higher than 30%. However, the combustion efficiency is impaired by the higher residual gas fraction in some operation points that leave room for improvements.

Effect of fuel injection timing and injection pressure on performance in a hydrogen direct injection engine

The in-cylinder hydrogen fuel injection method (diesel engine) induces air during the intake stroke and injects hydrogen gas directly into the cylinder during the compression stroke. Fundamentally, because hydrogen gas does not exist in the intake pipe, backfire, which is the most significant challenge to increasing the torque of the hydrogen port fuel injection engine, does not occur. In this study, using the gasoline fuel injector of a gasoline direct-injection engine for passenger vehicles, hydrogen fuel was injected at high pressures of 5 MPa and 7 MPa into the cylinder, and the effects of the fuel injection timing, including the injection pressure on the output performance and efficiency of the engine, were investigated. Strategies for maximizing engine output performance were analyzed.The fuel injection timing was retarded from before top dead center (BTDC) 350 crank angle degrees (CAD) toward top dead center (TDC). The minimum increase in the best torque ignition timing improved, and the efficiency and excess air ratio increased, resulting in an increase in torque and decrease in NOx emissions. However, the retardation of the fuel injection timing is limited by an increase in the in-cylinder pressure. By increasing the fuel injection pressure, the torque performance can be improved by further retarding the fuel injection timing or increasing the fuel injection period. The maximum torque of 142.7 Nm is achieved when burning under rich conditions at the stoichiometric air-fuel ratio.

Exhaust emission characteristics of stoichiometric combustion applying to diesel particulate filter(DPF) and three-way catalytic converter(TWC)

Various researchers study after-treatment system (DPF, SCR, LNT, TWC) to meet the recent strengthening regulation. In this study, we consider the intake air applying to the simulated-EGR which is composed of synthetic constituents (e.g. air, N2, and CO2 gas). Intake air excessively used to simulated-EGR, proceeds with the stoichiometric air-fuel ratio combustion in the cylinder. This stoichiometric exhaust emission was passed through and converted in TWC as well as DPF after-treatment system. We discuss exhaust emission characteristics of stoichiometric combustion applying to DPF and TWC in compression ignition diesel engine. The maximum of the conversion efficiency of NOx is 85.7% at SOI of −18.2° CA. aTDC with simulated-EGR the smoke reduction efficiency of soot is high and is provided over 99% reduction under the stoichiometric condition with reduced O2 mole fraction by adding only N2 and with EGR.

Investigation of the combustion and fuel properties of slurry fuels formed by biomass and coal

In the study, the combustion and fuel properties of slurry fuels, which are formed by mixing biomass as agricultural waste, sludge swage and algae, and coal as lignite and anthracite in certain proportions, were investigated. The energy properties of new slurry fuels were compared with fossil fuels such as lignite and anthracite, according to the Van Krevelen diagram used. The required stoichiometric air-fuel ratio (SAFR) amount in the burner was calculated during the combustion process. The real fuel-air ratio (RFAR) amount in the burner was determined during the combustion process according to the excess air coefficient (λ) value of 1.5.; as agricultural waste Rice Husks (RH), Corn Cobs (CS), Walnut Shells (WS), Sunflower Shells (SS), Olive Cake (OC), Woodchips (WC) and as other biomass; Brown algae, sewage sludge have been used. As lignite, eight different types with low fuel properties and anthracite, which is the best coal fuel, were used. In the study, the H/C ratio was found to be 1.126 for the mixture of Anthracite + Sewage Sludge + Sunflower Shells (SS) depending on the sewage sludge for the slurry fuels mixture. If it is dependent on Algae, a value of 1.243 was calculated for the mixture of Muğla Ikizköy + Algae + Sunflower Shells (SS). The O/C ratio was found to be 0.242 for Anthracite + Sewage Sludge + Olive Cake (OC) depending on the sewage sludge for the slurry fuels mixture. For Algae, a value of 0.129 was calculated for the mixture of Anthracite + Algae + Olive Cake (OC).

HARDWARE AND SOFTWARE OF AUTOMATIC CONTROL SYSTEM OF FUEL COMBUSTION PROCESS IN LOW AND MEDIUM POWER BOILERS. PART 2. ALGORITHMIC SOFTWARE

The efficiency of the functioning of boiler units depends on the availability of reliable information on the progress of technological processes. The lack of control and measuring systems for the composition of the exhaust gases leads to low efficiency of the boiler unit, in particular, due to poor-quality fuel combustion. Therefore, in modern operating conditions of boiler units, it is relevant to develop technological solutions focused on finding and minimizing the causes and mechanisms of the formation of harmful substances in exhaust gases.
 Due to the fact that replacement of outdated boiler units with new ones requires significant capital investments, a promising direction is the modernization of existing boiler units. It is a low-cost and efficient way of rational use of fuel while simultaneously reducing the level of harmful substances in exhaust gases. It remains relevant to ensure the functioning of the control systems for the composition of the air-fuel mixture (AFM) with a given speed and high reliability of maintaining the excess air ratio (EAR) at the stoichiometric level.
 In the article the high-quality algorithm is proposed for the operation of an automatic control system for the combustion of fuel in boilers of medium and low power by regulating the ratio of the components of the AFM for the burner with feedback according to the signals of the oxygen sensor. The algorithms for the operation of the frequency regulator of the ratio of the components of the AFM in various operating modes are considered. The developed algorithms allowed maintaining the stoichiometric air-fuel ratio in the boiler furnace, reducing the level of toxic emissions into the atmosphere and increasing the boiler efficiency by optimizing the fuel combustion process. The AFM ratio programmer is made in the LM Programmer technical programming environment and works with Windows operating systems (XP, Vista, 7, 8, 10) and oxygen sensors manufactured by Bosch. The visualization of the control process of the fuel combustion process is made in the technical programming environment LogWorks 3 and operates in the environment of Windows operating systems.

The Effect of Variable Air–Fuel Ratio on Thermal NOx Emissions and Numerical Flow Stability in Rotary Kilns Using Non-Premixed Combustion

One of the quickest ways to influence both the wall temperature and thermal NOx emissions in rotary kilns is to change the air–fuel ratio (AFR). The normalized counterpart of the AFR, the equivalence ratio, is usually associated with premixed flames and studies of its influence on diffusion flames are inconsistent, depending on the application. In this paper, the influence of the AFR is investigated numerically for rotary kilns by conducting steady-state simulations. We first conduct three-dimensional simulations where we encounter statistically unstable flow at high inflow conditions, which may be caused by vortex stretching. As vortex stretching vanishes in two-dimensional flow, the 2D simulations no longer encounter convergence problems. The impact of this simplification is shown to be acceptable for the thermal behaviour. It is shown that both the wall temperature and thermal NOx emissions peak at the fuel-rich and fuel-lean side of the stoichiometric AFR, respectively. If the AFR continues to increase, the wall temperature decreases significantly and thermal NOx emissions drop dramatically. The NOx validation, however, shows different results and indicates that the simulation model is simplified too much, as the measured NOx formation peaks at significantly fuel-lean conditions.

Effect of compression ratio on engine knock, performance, combustion and emission characteristics of a bi-fuel CNG engine

Compressed natural gas (CNG) is considered one of the most promising alternative fuel used in the transport sector. CNG has high octane number, wide flammability limit, and high H/C ratio, brings in important aspects regarding its feasibility as a fuel for internal combustion engines. It is necessary to have a dedicated engine rather than retrofitted, bi-fuels or dual-fuel ones to exploit the full potential of CNG properties. Most vehicles use the CNG in bi-fuel mode, where the fuel system is modified to operate either on gasoline or CNG. Therefore, the engine's compression ratio (CR) needs to be determined according to gasoline fuel requirement. However, CNG can be used at a higher CR, and the performance of the engine can be improved. The aim of this study is to investigate the effect of CR on knock intensity, performance, combustion, and emissions of a spark ignition (SI) engine fuelled with gasoline and CNG. Gasoline and CNG engine's performance were compared at different CRs and stoichiometric air-fuel ratio. The results show that the knock intensity was high at CR 12 and 7 bar indicated mean effective pressure (IMEP) for the gasoline-fueled engine. The maximum CR was limited to 12 for the gasoline engine. However, Knock was not observed even at CR 16 for the CNG engine. The engine was successfully operated at CR 16 with CNG. The performance and emission of the engine were also compared and presented. Fuel consumption and thermal efficiency were improved for CNG at higher CR compared to the gasoline engine.

INVESTIGATION OF PERFORMANCE AND EMISSION CHARACTERISTICS OF AN SI ENGINE FITTED WITH ZEOLITE-COATED CATALYTIC CONVERTER FOR VARIOUS ETHANOL-GASOLINE BLENDS

Ethanol blended in gasoline will produce more NOx emissions, compared to the conventional engine working under a stoichiometric air-fuel ratio. But, the emission control regulatory bodies tightened the emission level year by year. So, in our present work, a new metal-doped zeolite (as a catalyst)-coated monolith catalytic converter (CC) is developed and tested in the twin-cylinder multipoint fuel injection (MPFI) petrol engine using ethanol-gasoline blended fuels (P100, P95, P90, P85, and P80) (the numbers following P indicate percentage of the volumetric amount of gasoline). Initially, the engine was tested without a catalytic converter at various designated speed levels (2200, 2400, 2600, 2800, and 3000 rpm) and the emissions such as CO, HC, NOx, CO2, and O2 were calculated by an AVL 444 Di-gas analyzer at each speed level. The emission levels were compared and it was found that P80 blended fuel gives less emission. So, P80 blended fuel alone was taken for further investigation. Then, the market available catalytic converter was linked immediately to the exhaust gas outflow and a similar procedure was continued. Likewise, the testing was conducted with a new in-house-made Cu-ZSM5 zeolite catalytic converter. Outcomes from these experiments revealed that Cu-ZSM5 zeolite-based catalytic converter reduces NOx emission by 29% more effective than the market available catalytic converter for all the speeds.

The Issues of the Air-Fuel Ratio in Exhaust Emissions Tests Carried out on a Chassis Dynamometer

Vehicle exhaust emission tests use exhaust sampling systems that dilute the exhaust gas with ambient air. The dilution factor DF is calculated assuming that the combustion is complete, and that the engine is operated at a stoichiometric air-fuel ratio (AFR). These assumptions are not always met. This is especially true for diesel engines. This article discusses the tests to find out what the average lambda (λ) over the ARTEMIS, WLTC and NEDC driving cycles is and how this affects the result of the emission measurements. Measurements were carried out on a chassis dynamometer equipped with a standard emission measurement system used during the homologation. The λ was calculated using the Brettschneider equation. The dilution ratio DR was also determined by measuring the CO2 concentration in the raw exhaust gas. The CO2-tracer method used for this was modified. The median of the λ for a CI vehicle was 1.23–3.31, which makes the relative percentage difference between the DF and DR (ΔDF) in the range of 28–167%. For a SI vehicle homologated under the WLTP procedure, the median of the λ for the WLTC and ARTEMIS cycles was close to one and ΔDF for most cycles does not exceed 10%. In order to reduce the influence of the error of DF determination on the result of the emission measurement, it is recommended to use exhaust gas sampling systems that allow to determine the actual dilution ratio or to use the lowest possible dilution. The PAS-CVS system seems to be the most promising.

Comparison of Excess Air (Lean) vs EGR Diluted Operation in a Pre-Chamber Air/Fuel Scavenged Dual Mode, Turbulent Jet Ignition Engine at High Dilution Rate (~40%)

<div class="section abstract"><div class="htmlview paragraph">Charge dilution is widely considered as one of the leading strategies to realize further improvement in thermal efficiency from current generation spark ignition engines. While dilution with excess air (lean burn operation) provides substantial thermal efficiency benefits, drastically diminished NOx conversion efficiency of the widely used three-way-catalyst (TWC) during off-stoichiometric/lean burn operation makes the lean combustion rather impractical, especially for automotive applications. A more viable alternative to lean operation is the dilution with EGR. The problem with EGR dilution has been the substantially lower dilution tolerance limit with EGR and a consequent drop in thermal efficiency compared to excess air/lean operation. This is particularly applicable to the pre-chamber jet ignition technologies with considerably higher lean burn capabilities but much lower EGR tolerance due to the presence of a high fraction of residuals inside the pre-chamber. Dual Mode, Turbulent Jet Ignition (DM-TJI) technology with its unique ability to work with high external EGR dilution (up to 40% wet/mass basis) due to its additional air delivery to the prechamber offers a viable alternative to the lean burn strategy. DM-TJI could be the technology pathway to realize high EGR diluted combustion with comparable dilution limits to those of the lean burn strategy while still enabling effective use of TWC technology. Present study compares the excess air versus EGR dilution strategy under identical level of dilution (up to 40 %) in a DM-TJI equipped single cylinder engine operating on a high (13.3: 1) compression ratio. The results show that compared to the lean burn operation, EGR dilution provides marginally lower but still comparable thermal efficiency benefits with a marked improvement in NOx reduction, especially in a high compression, knock limited situation. This study showcases that high EGR dilution rates comparable to lean burn operation can be maintained with the DM-TJI system to achieve high thermal efficiency while still operating at stoichiometric air-fuel ratio.</div></div>

INVESTIGATION ON THE AIR-GAS CHARACTERISTICS OF AIR-HYDROGEN MIXER DESIGNED FOR DUAL FUEL – ENGINES

High smoke emissions, nitrogen oxide and particulate matter typically produced by diesel engines. Diminishing the exhausted emissions without doing any significant changes in their mechanical configuration is a challenging subject. Thus, adding hydrogen to the traditional fuel would be the best practical choice to ameliorate diesel engines performance and reduce emissions. The air hydrogen mixer is an essential part of converting the diesel engine to work under dual fuel mode (hydrogen-diesel) without any engine modification. In this study, the Air-hydrogen mixer is developed to get a homogenous mixture for hydrogen with air and a stoichiometric air-fuel ratio according to the speed of the engine. The mixer depends on the balance between the force exerted on the head surface of the valve and the opposite forces (the spring and friction forces) and its relation to decrease and increase the fuel inlet. Computational fluid dynamics (CFD) analysis software was utilised to study the hydrogen and airflow behaviour inside the mixer, established by 3.2 L engine. The Air-hydrogen mixer is examined with different speeds of engine1000, 2000, 3000 and 4000 RPM. Results showed air-hydrogen mixture was homogenous in the mixer. Furthermore, the stoichiometric air-fuel ratio was achieved according to the speed of the engine, the developed mixer of the AIR-Hydrogen mixing process provides high mixing homogeneity and engines with stoichiometric air-fuel ratios, which subsequently contributes to the high levels of efficiency in engine operation. In summary, the current study intends to reduce the emissions of gases and offer a wide range of new alternative fuels usage. While the performance of the diesel engine with the new air-hydrogen mixer needs to be tested practically.

Gasoline fuels properties for multi-mode operation – Observations in a GDI and the CFR engine

The combustion behavior of five full boiling range RON98 gasoline blends was evaluated for multi-mode operation in a GDI and the CFR octane rating engine. The GDI engine tests were conducted with stoichiometric air-fuel ratio in spark-ignition (SI), and with air-diluted homogeneous charge compression ignition (HCCI) mode. In the CFR engine, the knocking combustion was analyzed under standard RON testing conditions at both peak knocking lambda and stoichiometric air-fuel ratios, whereas compression ignited operation was characterized by utilizing the HCCI number test protocol. Disparate knock limited SI and HCCI combustion behavior was observed for the test fuels, despite four of the fuels having the same RON and octane sensitivity. It was found that knock-limited combustion phasing in the GDI engine did not align well with the RON. However, a detailed comparison of knock-limited SI operation in the GDI and CFR engine revealed that a more appropriate effective RON based on a common knock intensity metric (MAPO) and stoichiometric air-fuel ratio resulted in comparable knock characterization between the two engine platforms. Furthermore, the critical intake air temperature and the critical compression ratio were proposed to characterize knock-limited SI operation, while the minimum intake air heating and compression ratio were used to define a fuel’s autoignition propensity for compression ignition operation in the GDI and CFR engine, respectively. Finally, each fuel’s characteristic compression ratio needed to obtain knock-limited SI (KLSI) and HCCI operation was used to calculate an effective multi-mode octane number (MM-ON) based on the primary reference fuel blends.

The Effects of Use of the Range Extender in a Small Commercial Electric Vehicle

Research on the effects of the use of the range extender developed for a small commercial electric vehicle was presented in this paper. The range extender has a maximum output power of 2.65 kW. The developed auxiliary power unit consists of a three-phase generator propelled by an industrial low-power spark-ignition engine. The exhaust system was improved using a more efficient muffler. The implemented motorcycle muffler has a three-way catalyst (TWC) integrated inside. The use of the more advanced exhaust system aimed at reducing noise and exhaust emissions of the range extender. The efficient operation of the three-way catalytic converter requires a stoichiometric air-fuel ratio. To enable desired air-fuel ratio a fuel system was modified. In the first stage of research, the effects of improvements of the exhaust system on the range extender noise emissions were quantified. The next step covered the research of the fuel conversion efficiency, the exhaust gas composition, and the efficiency of conversion of the three-way catalyst. A significant decrease of noise and toxic gas emissions and an increase in the fuel conversion efficiency were revealed. The mentioned research was conducted in stationary conditions. After that, in the final part research of the running vehicle with the range extender on was made. The beneficial outcome of these tests enabled the development of a set of rules of the control of the range extender.

Design improvement of compressed natural gas (CNG)-Air mixer for diesel dual-fuel engines using computational fluid dynamics

This project carried out a computational fluid dynamics (CFD) analysis using ANSYS Fluent 14.5 software to design a compressed natural gas (CNG)-air mixer for CNG-diesel dual fuel engine. This study aimed to examine the performance of existing secondary fuel premixing controller (SFPMC) commercial mixer and modify its design in terms of air fuel ratio (AFR) and CNG-air mixture homogeneity (CAMH). The design modification of the mixer involved changing the surface of control valve shaft, gas manifold, position and directions of the CNG outlet holes. Results from simulation indicated that the original mixer was unable to control AFR since it changed from 8 at the engine speed of 1000 rpm to 176.39 at the engine speed of 3600 rpm when gas inlet pressure is fixed. However, AFR for the optimized mixer is between 17.21 and 17.4, a range close to stoichiometric AFR with various engine speeds and specific locations of the control valve. In terms of CNG-air mixture homogeneity, the uniformity index (UI) of methane mass fraction (MCh4) at the outlet of the original mixer is between 0.555 when engine speed is 1000 rpm and 0.578 when engine speed is 3600 rpm. However UI of MCh4 at the outlet of optimized mixer is between 0.995 when engine speed is 1000 rpm and 0.961 when engine speed is 3600 rpm. That means the CNG and air are homogeneously mixed at the outlet of optimized mixer in comparison with the original mixer. In summary, changing the surface of control valve shaft from cylindrical to conical shape lead to gradually opening the gas way and allow to rising the gas flow rate with increasing of air mass flow rate due to growing of engine speed, so the AFR is controlled in comparison with the origin mixer. Besides, changing the asymmetrically distributed seven gas injection holes near the mixer outlet to equal distribution 10 gas injection holes far from the mixer outlet perpendicularly to the air flow stream resulted in excellent homogeneity of the air and gas mixture in the optimized mixer.

Effects of hydrogen direct injection on combustion and emission characteristics of a hydrogen/Acetone-Butanol-Ethanol dual-fuel spark ignition engine under lean-burn conditions

Acetone-Butanol-Ethanol (ABE) is an essential product in the production process of butanol, which is considered as an effective way to replace butanol used in engines because of the lower production cost of ABE. Hydrogen is an ideal fuel for engines because of its low ignition energy and high flame propagation speed. In this study, the effects of hydrogen addition on the combustion and emission characteristics of a spark ignition ABE engine under lean-burn conditions are investigated. Specifically, five hydrogen blending ratios (0, 5%, 10%, 15%, 20%) and three λ values (1, 1.1, 1.2) are studied. The results show that adding hydrogen can increase the maximum cylinder temperature and pressure, decrease the flame development and propagation duration of the hydrogen/ABE dual-fuel SI engine. In addition, hydrogen addition can reduce the COVIMEP, BSFC, CO, HC emissions, and improve the IMEP, but increase NOx emissions; however, a lower NOx emissions for the hydrogen/ABE engine working under learn-burn conditions (λ equals 1.2) can be achieved with a suitable proportion of hydrogen adding (proportion = 5%) than that of engine working under stoichiometric air-fuel ratio condition. Thus, hydrogen addition can facilitate the combustion of ABE in engines, especially under lean-burn conditions.

Ability of Particulate Matter Index to describe sooting tendency of various gasoline formulations in a stratified-charge spark-ignition engine

This study investigates the ability of Particulate Matter Index (PMI) to describe the sooting behavior of various gasoline formulations in a stratified-charge (SC) spark-ignition engine. The engine was operated at 2000 rpm with an intake pressure of 130 kPa where soot formation is known to primarily occur in the bulk gases. Exhaust soot emissions were measured for nine test fuels at various exhaust gas recirculation levels. A comparison between measured soot levels and PMI shows that PMI is a relatively poor predictor of the sooting tendency of the tested fuels under lean SC combustion. Among the fuels, three fuels, namely the di-isobutylene blend, High Olefin, and E30 fuels exhibit measured soot behavior opposite of that predicted by PMI. Optical diagnostics were utilized to further investigate the in-cylinder phenomena for these three fuels. Analysis of natural luminosity and diffused back-illumination extinction imaging suggests that fuel-induced differences in the amount of soot formed are responsible for a majority of the discrepancy in measured versus predicted sooting tendency. Fuel-induced differences in soot oxidation and spray development seem to play minor roles. Because the combustion and air-fuel mixing processes for lean SC combustion are different from conventional stoichiometric operation it is hypothesized that the PMI correlation needs to be modified to account for differences in stoichiometric air-fuel ratio and level of oxygenation between fuels. Furthermore, the role of fuel volatility in PMI possibly needs to be de-emphasized for SC operation with fuel injection into compression-heated gases.

Numerical Study on the Required Surrounding Gas Conditions for Stable Autoignition of an Ethanol Spray

This study deals with the development of controlled-ignition technology for high-performance compression ignition alcohol engines. Among the alcohol fuels, we focus on ethanol as it is a promising candidate of alternative fuels replacing petroleum. The objective of this study is to reveal the physical and chemical phenomena in the mixture formation process up to autoignition of an ethanol spray. In our previous numerical study, we showed the mixture formation process for gas oil and ethanol sprays in the form of spatial excess air ratio and temperature distributions inside a spray and their temporal histories from fuel injection. The results showed a good agreement with those of theoretical analysis based on the momentum theory of spray penetration. Calculation was also confirmed as reasonable by comparing to the experimental results. Through the series of our experimental and numerical studies, the reason for poor autoignition quality of an ethanol spray was revealed, that is, difficulty in simultaneous attainments of autoignition-suitable concentration and temperature in the spray mixture formation due to its fuel and thermal properties of smaller stoichiometric air-fuel ratio and much greater heat of evaporation compared to conventional diesel fuels. However, autoignition of an ethanol spray has not been obtained yet in either experiments or numerical analysis. As the next step, we numerically examined several surrounding gas pressure and temperature conditions to make clear the surrounding gas conditions enough to obtain stable autoignition. One of the commercial CFD codes CONVERGE was used in the computational calculation with the considerations of turbulence, atomization, evaporation, and detailed chemical reaction. Required surrounding gas pressure and temperature for stable autoignition with acceptable ignition delay of an ethanol spray and feasibility of the development of high-performance compression ignition alcohol engines are discussed in this paper.