Fuel injection characteristics of diesel‐stimulated natural gas combustion

Although dual‐fuel (DF) engines using a low cetane number primary fuel such as natural gas (NG) ignited by a pilot diesel spray have been the subject of much investigation over years, there are still many unknown problems related to the fundamental combustion process of two fuels. In this work, a quiescent constant volume combustion bomb and a 3‐D numerical model have been used to study the effects of injection nozzle characteristics on the combustion of pre‐mixed NG/air with pilot distillate spray. Experimental tests were conducted on combustion process of pre‐mixed natural gas/air with pilot injection pressure of 30 and 20 MPa with a 4 hole injector, and also with injector nozzle of 8 and 4 holes. The global results obtained from computations compared well with the experimental results. Copyright © 1999 John Wiley & Sons, Ltd.     

柴油机混合气形成条件对瞬态火焰温度和碳烟质量浓度影响的研究

进气涡流强度、喷嘴的喷孔直径与个数、喷油压力等直接影响直喷式柴油机燃烧室内混合气形成与燃烧过程的进行，从而影响柴油机的动力性、燃油经济性和碳烟排放。作者用同步光导纤维四色法测量系统，研究了进气涡流、喷孔直径和个数对燃烧过程中火焰温度和碳烟浓度的影响。本文介绍的是所进行的研究工作和得到的结果。     

Experimental investigation concerning the influence of fuel type and properties on the injection and atomization of liquid biofuels in an optical combustion chamber

Due to the scarcity of fossil fuels and the future stringent emission limits, there is an increasing interest for the use of renewable biofuels in compression ignition engines. However, these fuels have different physical, chemical and thermodynamic properties affecting atomization, spray development and combustion processes. The results reported in this paper have been obtained by experimentation with a constant volume combustion chamber. The influences of physical fuel properties on injections under non-evaporating conditions are studied, using a pump-line-nozzle system from a medium speed diesel engine with injection pressures up to 1200 bar, by changing the fuel type and temperature. Experiments were conducted for diesel, biodiesel, straight vegetable oils and animal fats. Injection pressure and needle lift measurements were analyzed. A high speed camera was used to visualize the spray, which enabled us to study the spray penetration and spray angle. Our results show that the fuel temperature is an important parameter to control because it significantly affects the fuel properties. Both the injection timing and injection duration are affected by the fuel properties. The influences of these properties on the spray development were less pronounced. At low temperatures, a strongly deteriorated atomization of oils and fats was observed.     

Combustion performance and emission reduction characteristics of automotive DME engine system

This article is a condensed overview of a dimethyl ether (DME) fuel application for a compression ignition diesel engine. In this review article, the spray, atomization, combustion and exhaust emissions characteristics from a DME-fueled engine are described, as well as the fundamental fuel properties including the vapor pressure, kinematic viscosity, cetane number, and the bulk modulus. DME fuel exists as gas phase at atmospheric state and it must be pressurized to supply the liquid DME to fuel injection system. In addition, DME-fueled engine needs the modification of fuel supply and injection system because the low viscosity of DME caused the leakage. Different fuel properties such as low density, viscosity and higher vapor pressure compared to diesel fuel induced the shorter spray tip penetration, wider cone angle, and smaller droplet size than diesel fuel. The ignition of DME fuel in combustion chamber starts in advance compared to diesel or biodiesel fueled compression ignition engine due to higher cetane number than diesel and biodiesel fuels. In addition, DME combustion is soot-free since it has no carbon–carbon bonds, and has lower HC and CO emissions than that of diesel combustion. The NO_x emission from DME-fueled combustion can be reduced by the application of EGR (exhaust gas recirculation). This article also describes various technologies to reduce NO_x emission from DME-fueled engines, such as the multiple injection strategy and premixed combustion. Finally, the development trends of DME-fueled vehicle are described with various experimental results and discussion for fuel properties, spray atomization characteristics, combustion performance, and exhaust emissions characteristics of DME fuel.     

Hydrogen enrichment of methane and syngas for MILD combustion

Moderate or Intense Low-oxygen Dilution (MILD) combustion is a technology with important characteristics such as significant low emission and high-efficiency combustion. The hydrogen enrichment of conventional fuels is also of interest due to its favorable characteristics, such as low carbon-containing pollutants, high reaction intensity, high flammability, and thus fuel usage flexibility. In this study, the effects of adding hydrogen to methane and syngas fuels have been investigated under conditions of MILD combustion through numerical simulation of a well-set-up MILD burner. The Reynolds-Averaged Navier-Stokes (RANS) approach is adopted along the Eddy Dissipation Concept (EDC) combustion model with two different chemical mechanisms. Molecular diffusion is modeled using the differential diffusion approach. The effects of oxidizer dilution and fuel jet Reynolds number on the reactive flow field have been studied. Results show that with an increase in hydrogen portion of the fuel mixtures, the volume of the high-temperature region of combustion field increases whereas a reduction of oxidizer oxygen content leads to more proximity to the MILD condition. Increasing the fuel jet Reynolds number will result in an expansion of the combustion zone and shifting of this region in the axial direction. Predictions revealed that the methane flame is more sensitive to the oxidizer dilution and fuel jet Reynolds number than syngas. Moreover, enrichment of fuel with hydrogen seems to be better for acquiring condition of the MILD combustion for syngas rather than methane. Indeed, syngas shows more sensitivity to hydrogen enrichment than methane, which makes hydrogen a good additive to syngas in terms of MILD condition benefits.     

A review of investigations on liquid fuel combustion in porous inert media

Utilization of a porous medium for combustion of liquid fuels is proved to be a promising approach for future applications. The porous medium burner for liquid fuels is more advantageous than the conventional open spray flame burner for several reasons; these include enhanced evaporation of droplet spray owing to regenerative combustion characteristics, low emission of pollutants, high combustion intensity with moderate turn-down ratio and compactness. This article provides a comprehensive picture of the global scenario of research and developments in combustion of liquid fuels within a porous medium that enable a researcher to determine the direction of further investigation. Accordingly, a glossary of the important terminology, the modeling approach, advances in numerical and experimental works and applications are included. The papers published in standard journals are reviewed and summarized with relevant comments and suggestions for future work.     

Effects of nozzle geometry on direct injection diesel engine combustion process

The aim of the current article is to link nozzle geometry, and its influence on spray characteristics, with combustion characteristics in the chamber. For this purpose, three 6-hole sac nozzles, with different orifices degree of conicity, have been used. These nozzles had been geometrically and hydraulically characterized in a previous publication, where also a study of liquid phase penetration and stabilized liquid length in real engine conditions has been done. In the present work, CH and OH chemiluminescence techniques are used to thoroughly examine combustion process. CH-radicals are directly related to pre-reactions, which take place once the fuel has mixed with air and it has evaporated. On the other hand, OH-radicals data provide information about the location of the flame front once the combustion has begun. The analysis of all the results allows linking nozzle geometry, spray behaviour and combustion development. In particular, CH-radicals have shown to appear together with vapor spray, both temporally and in their location, being directly related to nozzle characteristics. Additionally, analysis of ignition delay is done form OH measurements, including some correlations in terms of chamber properties, injection pressure and nozzle diameter.     

Modeling HCCI combustion of biofuels: A review

The ever increasing energy demands coupled with the limited availability of fossil fuels and the detrimental environmental effects resulting from their use, has guided research toward seeking alternative fuels to gradually substitute conventional ones. Among these, biofuels have received increasing attention due to their attractive features of being renewable in nature and reducing the net CO₂ emissions. Biofuels have been used in conventional diesel and gasoline engines either as neat fuels or as supplements.Fortunately, a relatively new combustion concept for internal combustion engines, namely homogeneous charge compression ignition (HCCI) combustion, has been evolved in parallel to the biofuel research. HCCI combustion seems to be able to take advantage of the diverse properties of biofuels, since in this combustion mode ignition is not externally instigated, but relies on the compression and subsequent autoignition of a fuel-air mixture. This fact allows the utilization of different fuels or blends thereof, in order to regulate the ignition point and provide adequate operation under diverse operating conditions.This study provides an overview of existing simulation models for the simulation of biofueled HCCI combustion. Simulation models aid and supplement the experimental research conducted on HCCI combustion, providing a fundamental insight into the physicochemical parameters affecting performance and emissions formation. The simulation models include single-zone models, multi-zone models, probability based models, and multi-dimensional models in order of complexity. The vast majority of these models implement chemical kinetics to simulate the combustion process, not only due to the inherent dependence of HCCI combustion on the physicochemical properties of the fuel, but also due to the sometimes complex chemical structure of the biofuels, which include esters, ethers and alcohols. The reaction paths for these homologous series are quite different from the conventional hydrocarbons used to simulate conventional fuels, and provide the ground for current and future research work.     

Fuel design and management for the control of advanced compression-ignition combustion modes

Due to concerns regarding the greenhouse effect and limitations on carbon dioxide emissions, the possibility of a next-generation combustion mode for internal combustion engines that can simultaneously reduce exhaust emissions and substantially improve thermal efficiency has drawn increasing attention. The most prominent characteristic of new combustion modes, such as Homogenous-Charge Compression-Ignition (HCCI), Stratified-Charge Compression-Ignition (SCCI), and Low-Temperature Combustion (LTC), is the requirement of creating a homogenous mixture or controllable stratified mixture prior to ignition. To this end, a lean fuel/air mixture and/or a controllable high level of exhaust gas recirculation (EGR) are employed to prolong the timescale of the ignition chemistry and port fuel injection or early in-cylinder injection is used to lengthen the mixing period. The mixture then undergoes controlled self-ignition near the top dead center (TDC) position due to the compression effect of the piston’s upward movement. It is worth noting that the entire combustion process lacks a direct method for the control of ignition timing and combustion rate, which are instead controlled primarily by chemical kinetics and, to a lesser extent, by turbulence and mixing. Because of the significant impacts of fuel physical–chemical properties on the ignition and combustion process, fuel design and management has become the most common approach for the control of ignition timing and combustion rate in such advanced combustion modes.This paper summarizes the concepts and methods of fuel design and management and provides an overview of the effects of these strategies on ignition, combustion, and emissions for HCCI, LTC, and SCCI engines, respectively. From part 2 to part 4, the paper focuses on the effect of fuel design on HCCI combustion. A fuel index suitable for describing ignition characteristic under HCCI operating conditions is first introduced. Next, the proposed fuel design concept is described, including principles and main methodologies. Strategies based on the fuel design concept (including fuel additives, fuel blending, and dual-fuel technology) are discussed for primary reference fuels (PRF), alternative fuels, and practical gasoline and diesel fuels. Additionally, the effects of real-time fuel design on HCCI combustion fueled with PRFs and dimethyl ether/liquefied petroleum gas (DME–LPG) are evaluated. Diesel HCCI combustion has suffered from difficulties in homogenous mixture formation and an excessively high combustion rate. Therefore, LTC, which concentrates on local combustion temperature and a balance of mixture formation timescale and ignition timescale, has been proposed by many researchers. In Part 5, this paper provides an overview of the major points and research progress of LTC, with a preliminary discussion of the fundamental importance of fuel properties and fuel design strategy on the LTC process and emissions. Due to the stratification strategy has the capable of extending the HCCI operation range to higher loads, SCCI combustion, which incorporates HCCI combustion into a traditional combustion mode, has the potential to be used in commercial engines. Thus, this paper discusses the principles and control strategies of fuel design and management and also summarizes recent progress and future trends. The effect of fuel design and management on SCCI combustion is assessed for high cetane number fuels and high octane number fuels as well as the in SCCI combustion of gasoline–diesel dual-fuel and blends.     

Performance,emission and combustion characteristics of a compression ignition engine operating on neat orange oil

Biomass derived fuels are preferred as alternate fuels for I.C Engines due to their abundant availability and renewable nature. Fuels such as methanol and ethanol have proved to be suitable alternate fuels in the transport sector. In the present work the performance, emission and combustion characteristics of a single cylinder, constant speed, direct injection diesel engine using orange oil as an alternate fuel were studied and the results are compared with the standard diesel fuel operation. Results indicated that the brake thermal efficiency was higher compared to diesel throughout the load spectra. Carbon monoxide (CO) and hydrocarbon (HC) emissions were lower and oxides of nitrogen (NO_x) were higher compared to diesel operation. Peak pressure and heat release rate were found to be higher for orange oil compared to diesel fuel operation.     

Science review of internal combustion engines

Internal combustion engines used in transportation produce about 23% of the UK's carbon dioxide emission, up from 14% in 1980. The current science described in this paper suggests that there could be 6–15% improvements in internal combustion fuel efficiency in the coming decade, although filters to meet emission legislation reduce these gains. Using these engines as hybrids with electric motors produces a reduction in energy requirements in the order of 21–28%. Developments beyond the next decade are likely to be dominated by four topics: emission legislation and emission control, new fuels, improved combustion and a range of advanced concepts for energy saving. Emission control is important because current methods for limiting nitrogen oxides and particulate emissions imply extra energy consumption. Of the new fuels, non-conventional fossil-derived fuels are associated with larger greenhouse gas emissions than conventional petroleum-based fuels, while a vehicle propelled by fuel cells consuming non-renewable hydrogen does not necessarily offer an improvement in emissions over the best hybrid internal combustion engines. Improved combustion may be developed for both gasoline and diesel fuels and promises better efficiency as well as lower noxious emissions without the need for filtering. Finally, four advanced concepts are considered: new thermodynamic cycles, a Rankine bottoming cycle, electric turbo-compounding and the use of thermoelectric devices. The latter three all have the common theme of trying to extract energy from waste heat, which represents about 30% of the energy input to an internal combustion engine.     

Impact of alternative fuel properties on fuel spray behavior and atomization

In order to verify and solve the problem of NOx and PM emissions, it is necessary to directly observe the internal combustion chamber of a diesel engine. Many studies have been performed in recent years to verify the macroscopic and microscopic behavior of the injected fuel spray because observing it is not easy due to the difficulties of the experiment. Researchers have investigated the spray characteristics for various diesel injector nozzles over a wide range of temperatures and pressure, but there is lack of evaluation for the spray characteristics for biodiesel. At a time when rapid rise of fuel prices and depleting hydrocarbon resources of the world have forced us to look for alternative fuels biodiesel produced by transesterification of non-edible vegetable oils is promising to be an important additive/substitute to petro diesel. Biodiesel being an oxygenated and sulfur-free fuel leads to more complete combustion and lower emissions. But, the energy content or net calorific value of biodiesel is less than that of diesel fuel; also it has higher viscosity and density, than diesel fuel. A considerable improvement in these properties can be obtained by mixing diesel and biodiesel and then using the blends. Biodiesel and biodiesel/petro diesel blends, with their higher lubricity levels, are increasingly being utilized as an alternative. Present paper analyzed the correlation of injection parameters that will affect the spray characteristics of biodiesel. Observations for analyzing the effect of injection parameters on spray cone angle, break up length and fuel penetration were made. Finally the performance and emissions tests were studied. Atomization and vaporization of fuel are greatly influenced by viscosity and density of fuel and these properties are temperature dependent. Thus fuel inlet temperature plays a very important role in fuel atomization process. At higher temperature viscosity of fuel decreases which enhances the atomization of biofuels.     

Spray combustion of fast pyrolysis bio-oils: Applications,challenges, and potential solutions

This article provides a comprehensive review of the spray combustion of fast pyrolysis bio-oil (FPBO, also called bio-oil, pyrolysis oil or pyrolysis liquid biofuel), which is widely regarded as one of the most economically feasible renewable resources to facilitate the replacement of fossil oils. The utilization of FPBO as a fuel is challenging due to its unique atomization and combustion characteristics but it is important given the need to develop a more sustainable energy infrastructure. Significant efforts have been made in utilizing FPBO as a practical alternative fuel and the first FPBO facilities for heat and/or power generation have been brought online in recent years. FPBO-fueled burners, boilers, and furnaces are ready from a technical perspective for large-scale industrial use, and even small-scale systems show excellent flame stability, low emissions, and minimal requirements for secondary fuel usage. FPBO applications in gas turbine and compression-ignition engines are technically more challenging, currently having had only limited successes in larger-scale units and for short time intervals in smaller ones. With recent research and technological advances, however, FPBO use in small-scale combustion engines appears to be technically feasible. In the literature, extensive research efforts have been dedicated to this topic either as a fuel itself or its utilization for practical applications. Nonetheless, inadequate considerations have been given to the critical role of FPBO atomization and its subsequent fuel/air mixing, which in turn controls the combustion efficiency and emission characteristics of a system. Understanding the spray combustion properties of FPBO is especially important because of the fuel's unfavorable properties compared to fossil oils including low energy density, high viscosity, high water content, containing suspended solid particulates and non-volatile residue, chemical instability, and an incompatibility with conventional fossil oils. The information presented herein, therefore, focuses on understanding the challenges and constraints that are unique to FPBO applications, along with proposing several strategies to properly atomize and combust this fuel in order to enhance combustion efficiency and reduce pollutant emissions in practical systems. Although substantial progress has been made in understanding the FPBO spray combustion as revealed by this review, better standardization of FPBO properties, more efficient techniques for optimizing atomization and combustion for different applications, and more studies to understand the long-term reliability of devices running on FPBO are needed.     

Cotton methyl ester usage in a diesel engine equipped with insulated combustion chamber

An important alternative for diesel fuel is methyl ester made of vegetable oils. Direct use these fuels without modification in diesel engines causes some damages on the parts of the engines and also, the viscosity of the methyl ester fuels is quite higher than that of diesel fuel (No. 2D) and their calorific value is lower. Therefore it is not possible to obtain more benefit. Coating combustion chamber parts with a ceramic material seems an effective solution for improving performance of these lower-quality fuels compared with No. 2D and also exhaust emission values. Since it allows to use higher combustion temperatures. In the present study, surfaces of cylinder head, piston, exhaust and inlet valve of a four-stroke, direct injection, single cylinder diesel engine were coated with molybdenum (Mo) by plasma spray method. Thus, thermal barrier characteristic was brought to these parts. Variances in performance and emission values of cotton methyl ester and 2D fuel mixtures were studied in the ceramic coated and uncoated engines under the same running conditions. Performance (up to 2.2–2.3% for engine power, up to 3.5–5.6% for specific fuel consumption) and emission values (up to 17–22% for CO, up to 5.2–10% for smoke) of the test fuels were improved in the coated engine compared with the uncoated engine. However, because the coated engine ran at higher temperatures compared with the uncoated engine, an increase (up to 6.5–7.4%) was seen in NO_x emission in cases of all test fuels.     

Comparisons of hydrogen and gasoline combustion knock in a spark ignition engine

Combustion knock is one of the primary constraints limiting the performance of spark-ignition hydrogen fuelled internal combustion engines (H2-ICE) as it limits the torque output and efficiency, particularly as the equivalence ratio nears stoichiometric operation. Understanding the characteristic of combustion knock in a H2-ICE will provide better techniques for its detection, prevention and control while enabling operation at conditions of improved efficiency.

Engine studies examining combustion knock characteristics were conducted with hydrogen and gasoline fuels in a port-injected, spark-ignited, single cylinder cooperative fuel research (CFR) engine. Characterization of the signals at varying levels of combustion knock from cylinder pressure and a block mounted piezoelectric accelerometer were conducted including frequency, signal intensity, and statistical attributes. Further, through the comparisons with gasoline combustion knock, it was found that knock detection techniques used for gasoline engines, can be applied to a H2-ICE with appropriate modifications. This work provides insight for further development in real time knock detection. This would help in improving reliability of hydrogen engines while allowing the engine to be operated closer to combustion knock limits to increase engine performance and reducing possibility of engine damage due to knock.     

A computational study on the combustion of hydrogen/methane blended fuels for a micro gas turbines

To understand the combustion performance of using hydrogen/methane blended fuels for a micro gas turbine that was originally designed as a natural gas fueled engine, the combustion characteristics of a can combustor has been modeled and the effects of hydrogen addition were investigated. The simulations were performed with three-dimensional compressible k-ε turbulent flow model and presumed probability density function for chemical reaction. The combustion and emission characteristics with a variable volumetric fraction of hydrogen from 0% to 90% were studied. As hydrogen is substituted for methane at a fixed fuel injection velocity, the flame temperatures become higher, but lower fuel flow rate and heat input at higher hydrogen substitution percentages cause a power shortage. To apply the blended fuels at a constant fuel flow rate, the flame temperatures are increased with increasing hydrogen percentages. This will benefit the performance of gas turbine, but the cooling and the NO_x emissions are the primary concerns. While fixing a certain heat input to the engine with blended fuels, wider but shorter flames at higher hydrogen percentages are found, but the substantial increase of CO emission indicates a decrease in combustion efficiency. Further modifications including fuel injection and cooling strategies are needed for the micro gas turbine engine with hydrogen/methane blended fuel as an alternative.     

Shock tube studies on ignition delay and combustion characteristics of oxygenated fuels under high temperature

A comparative study on ignition delay time and combustion characteristics of four typical oxygenated fuel/air mixtures of dimethyl ether (DME), diethyl ether (DEE), ethanol and E92 ethanol gasoline was conducted through the chemical shock tube. The fuel/air mixtures were measured under the ignition temperature of 1100 to 1800 K, initial pressure of 0.3 MPa and the equivalence ratios of 0.5, 1.0 and 1.5. The experimental results show that the ignition delay time of these four oxygenated fuels satisfies the Arrhenius relation. The reaction H + O₂ = OH + O has a high sensitivity in four fuel/air mixtures during high-temperature ignition, which makes the ignition delay lengthen with the increase of the equivalence ratios. By comparing the ignition delay of four fuels, ether fuels have excellent ignition performance and ether functional group has better ignition promotion than hydroxyl group. Moreover, the carbon chain length also significantly promotes the ignition. Due to the accumulation of a large number of active intermediates and free radicals during the long ignition delay time before ignition, the four fuels all have intense deflagration and generate the highest combustion peak pressure at the relatively low ignition temperature (1150-1300 K). For DME, DEE and ethanol, due to the high content of oxygen in their molecules, the combustion peak pressure and luminous intensity increased with the equivalence ratio, and the combustion is intense after ignition. E92 ethanol gasoline with low oxygen content has a lower combustion peak pressure and a longer combustion duration than the other three fuels, and its highest combustion peak pressure appears in the stoichiometric ratio. The combustion process of E92 ethanol gasoline is more oxygen-dependent than the other three fuels.     

闪急沸腾喷雾场粒度分布规律及燃烧特性的研究

用激光全息术对闪急沸腾喷雾场的粒度分布进行了测量研究。结果表明,与常温喷雾相比,闪急沸腾喷雾具有粒子平均直径小,轴向、径向分布均匀等特点。在一台单缸机上,采用闪急沸腾喷雾方式进行了燃用柴油和煤化油的试验研究。与常温喷雾相比,闪急沸腾喷雾燃烧方式可大大降低柴油机的碳烟和油耗率。用这种燃烧方式燃用煤化油的结果表明,闪急沸腾喷雾燃烧方式在柴油机燃用低十六烷值燃油方面具有巨大的潜力。     

The characteristics of air pollutants from the combustion of biomass pellets

Biomass is renewable clean energy. The aim of this study is to explore the combustion properties and emission characteristics of NO_X, SO₂, PM, and HCl in the combustion process of biomass pellet fuels. In this study, three kinds of fuels (pine sawdust, mixed wood, and corn straw) were selected to be studied by using a tube furnace to simulate industrial boiler. Experiments were conducted under different combustion conditions (combustion temperature and air flow). The results show that pollutant emissions were related to fuel type, combustion temperature, and air flow. The emissions of NO_X were contingent on N content in the fuel and the peak emissions of NO_X appeared in the range of 50~600 mg/m³ at 4 L/min and 700℃. The emissions of SO₂ were related to combustion condition and close to zero under the condition of sufficient combustion. The emissions of HCl and particulate matter (PM) increase with the rise of temperature, but the emission of PM was minimal at 800℃. Average HCl emission was 0.2~0.5 mg/g under steady-state conditions (4 L/min and 700℃). All in all, the pollutant emissions of biomass pellet fuels during combustion are lower than those of the traditional fuel, and the combustion efficiency is relatively higher.     

Effect of water blending on bioethanol HCCI combustion with forced induction and residual gas trapping

There is increased interest worldwide in renewable engine fuels as well as in new combustion technologies. Bioethanol is one of the alternative fuels that have been used successfully in spark ignition engines. A combustion technology that currently attracts a lot of interest is the homogeneous charge compression ignition (HCCI) combustion, which has shown potential for low nitrogen oxides emissions with no particulate matter formation. The authors have shown previously that applying forced induction to bioethanol HCCI with residual gas trapping results in an extended load range compared to naturally aspirated operation. However, at high boost pressures, high cylinder pressure rise rates develop. Work by other researchers has shown that direct injection of water can be used as a combustion control method. The present work explores water blending as a way that might have an effect on combustion in order to lower the maximum pressure rise rates and further improve emissions. The obtained experimental results show that in contrast to variable rate direct injection of water, fixed rate water–ethanol blending is counterproductive for the reduction of pressure rise rates at higher loads. In addition, increasing the water content in ethanol results in reduction of the effective load range and increased emissions.