1 Introduction

In the contest of the current automotive engine landscape, there is a requirement of an alternative viable source of energy. Alternative fuels are a substitute for the convention source of energy in the global prospects for engines. Alcohols are an alternative renewable source of energy which led to full-scale evolution and implementation as fuel in the engine which can operate at different percentages. Among the alternative fuels, biofuels are one of the examples of such type of development in the world scenario. Alcohol fueled engine is an IC engine which can run at a different percentage of methanol or ethanol and fuel can be stored in the same tank. These engines can burn any fraction of alcohol with conventional fuel by using controlling fuel injection timing i.e. by varying injection stretegies and methods.

Currently, methanol is used as an alternative fuel in various applications, and its trial was demonstrated in the early nineties. It is composed of coal, biomass, and renewable source of energy by carbon capturing and its scheme of utilization. It is a viable fuel having strong potential to cut down the carbon footprint of fossil fuel in the transport sector. It is used as a fuel blend or pure form in internal combustion engines. Thus methanol is a most attractive fuel as an alternative to conventional fuel as its qualities like making, liquid fuel, easy to store and distribution. The physical and chemical properties of convention fuel (gasoline), methanol, and ethanol are compared, as shown in Table 3.1. Methanol application in internal combustion engine increases the brake thermal efficiency hence enhances the energy utilization (Nichols 2003). It produces higher hydrocarbon and reduced NOx and soot in exhaust gas emission than convention fuel (Shamun et al. 2016). Thus it has advantages like sustainability, energy security, and air quality point of view.

Table 3.1 Physical and chemical properties of gasoline methanol and ethanol (Yates et al. 2010)
Full size table

Methanol chemical structure (CH3OH) contains oxygen which separates from convention fuel and causes wear or degradation and corrosion of engine components. Therefore engine parts components which come in contact with fuel are required to upgrade. As the current fuel price increased day-by-day, it is necessary to reduce by applying other fuel without changing the operational cost. The engine parts (fuel pump, engine valves, engine valve seats, fuel, and oil sealing materials) upgradation is necessary for compatibility of methanol (Hagen 1977).

In this study, methanol application as fuel in the internal combustion engine and the effect of methanol on the materials of engine components are elaborated in detail. The engine modification and design of methanol-fueled engine components are also studied.

2 Material Compatibility Issues for Methanol

The polarity of methanol leads to the challenge regarding material compatibility, which needs the changes in the fuel system of engines. Metals and elastomers used in fuel systems are attacked by methanol if the proper material selection is not done. Amongst alcohol methanol is most aggressive. Methanol and wet methanol are corrosive to iron, steel, magnesium, aluminum, zinc, copper and their alloys. Anodized aluminum is corrosion resistant to methanol (West and McGill 1992). Some rubber and plastic materials are sensitive to methanol, but there are some polymers which are not affected by methanol.

2.1 Fuel Chemistry and Quality Issues

Chemical structure and quality of fuel is important for the compatibility of the fuel delivery systems. Fuel delivery system is affected by the chemistry of fuel. The material testing of the components with methanol is necessary for the durability of the fuel delivery system. Methanol is very reactive with coating materials like aluminum oxide or aluminum. The reactions of methanol with aluminum and their oxides are as follows

$$ 6{\text{CH}}_{3} {\text{OH}} + {\text{Al}}_{2} {\text{O}}_{3} \; \to \;2{\text{Al}}\left( {{\text{OCH}}_{3} } \right)_{3} \, + \,3{\text{H}}_{2} {\text{O}} $$
(3.1)

The reaction product, methoxide salts are soluble in methanol. Aluminum also react with methanol to form methoxide.

$$ 6{\text{CH}}_{3} {\text{OH}} + 2{\text{Al}}\; \to \;2{\text{Al}}\left( {{\text{OCH}}_{3} } \right)_{3} \, + \,3{\text{H}}_{2} $$
(3.2)

The quality of fuel is very important for the robustness of the fuel delivery components. Impurities present in fuel would also affect the fuel delivery systems. For example injector operations are very much affected by sulfates, which are recorded as deposits in fuel injector and filter plugging (ASTM Standard 2009; Dumont et al. 2007; Devlin et al. 2005). Corrosion because of impurities like chlorides, and peroxides which are formed due to copper, would affected the elastomers seals and fuel delivery system, fuel economy, and emissions (Dumont et al. 2007; Brinkman et al. 1994). Hence, fuel specification of methanol should be improved.

2.2 Corrosion

Alcohols exposed to ferrous metals cause more corrosion than conventional fuels. Generally, corrosion is due to the impurities such as formic acid, acetic acid, and chlorides. Contaminant like chloride ion, formic acids present in alcohols causes enhanced corrosion (Walker and Chance 1983). Ethyl acetate, acetic acid and chloride ion all three together are more prone to corrosion than a single one. Formation of formic acid and acetic acid in alcohol fuel are common during combustion and enhance their corrosiveness. Methanol or ethanol which absorbed water make them electrically conductive, and any contaminant containing ions increases their conductivity, which enhances the electrochemical and galvanic corrosion. Azeotropic water present in alcohol causes the wet corrosion which oxidizes most of the metals (Brink et al. 1986). Methanol or ethanol and absorbed water enhanced the electrical conductivity of alcohol, resulting in higher corrosion. Organic contamination, such as formic acid enhances the corrosiveness of exhaust gases produced by alcohol combustion. Formic acid is an alcohol combustion product which brings down the corrosion temperature below the dew point of the engine exhaust gas. Peroxides are the alcohols combustion product, which increases the corrosion growth due to the alcohol combustion product. Metals like magnesium, aluminum, and lead are more susceptible to alcohol attack, which causes corrosion (Dela Harpe 1988). Contaminant in alcohol fuel enhanced the corrosion of the fuel handling system and also corrosiveness of combustion product. The main corrosion outcome is hydrated ferrous chloride, and it enhances the rust formation (Otto et al. 1986, 1988). Metals in contact with alcohols are prone to stress corrosion failure. The crack formed in fuel line enhances the corrosion possibility as metal exposes to alcohol.

Wing et al. (1993) have studied the corrosion of steel and aluminum substrate and also coated with a moderate and high percentage of phosphorus electroless nickel (chemical plating of nickel) for the gasoline and gasoline/methanol fuel test. The test was carried for the gasoline as reference fuel and gasoline with 15 and 85% of methanol for pure substrate and coatings. The electroless coatings over aluminum and steel and anodized aluminum exhibited the best corrosion protection under test conditions. Anodizing is an electrochemical process in which the metal surfaces are converted into an anodic oxide that is corrosion-resistant and highly durable. So these coatings can be used for methanol-fueled engines (Table 3.2).

Table 3.2 Corrosion performance methanol-fueled engine for different materials and coatings (Saarialho et al. 1982)
Full size table

2.3 Wear

Alcohols used as an alternative fuel causes the wear of metallic components. Wear of engine component is a very detracting concern, and numerous investigations have been performed to understand their sensitivity. Application of methanol as fuel in IC engine enhanced the wear of engine components. This is due to the formation of corrosive combustion products, which causes a reduction of oil films thickness. The intermediate combustion product such as formic acid promotes the wear of engine cylinder liner and piston ring assembly (Naegeli et al. 1997). Corrosion of piston ring and cam follower with the application of 15% blends of ethanol and methanol with conventional fuel (E15 and M15) is causes a significant amount of wear. The wear of engine components due to gasohol is firmly related to the corrosion of those components.

2.4 Components Affected by Methanol

Many engine components are affected by using alcohol and their blends as fuel. The compatibility of components material like metal or plastic or elastomers is studied. These components are fuel pumps, seals, fuel tanks, injectors, piston rings, pistons, engine cylinders, valves and valve seats. Fuel pump material must be changed or upgraded to enhance the fuel flow rate because the alcohols and their blends have lesser heating value. The fuel electrical conductivity increases when alcohol is used, so the fuel level sender (consist of an electrical resister) is upgraded or changed. The fuel line materials (metal or polymer) are affected by alcohols presence in the fuel. The improper material selection causes the wear, degradation, and corrosion of engine components and results in the fuel leaks. Therefore, engines are at higher risk by using alcohol fuel and material compatibility and hardware robustness are under suspects. The materials used in engine components (fuel injectors, fuel rails, and their seals) are influenced by the application of alcohols as a substitute fuels for IC engine. The other engine parts like cylinder head, piston rings, valve seat, engine valve, intake manifold, intake port, and various oil seals are also affected by the use of alcohols. Wear of some components increases due to combustion characteristics (peak pressure, temperature, emissions etc.) and the use of different fuels.

2.5 Fuel Handling

Material selection and design of fuel systems must be taken care when alcohols are used in the engine as fuel. Design of metallic components in contact with alcohol is very critical for fuel composition variation, thermal, and pressure effect. Different metals have been selected for the design of fuel tanks, fuel lines, fuel filters, level sensors, fuel pumps, pressure control valves, the liquid containing sensors, regulators and fuel modules. The metallic components materials and their design have been changed according to materials changing regulations. Many older designs which were according to conventional fuel should be validated for alcohols and modified by protective coating for methanol. So, optimal designs of components for alcohol fuels are taken care for the sustainability of methanol. The review of protective coating and metals used is necessary for the application of alcohols. Compatibility of components material is taken care of all ranges of operating conditions.

2.6 Fuel Tank Assembly

Compatibility of material and their corrosion resistance properties was considered for the application of alcohol as a fuel. Fuel tank materials are made of carbon steels, which are corroded by alcohols application. These carbon steels fuel tanks are coated with coating materials which are not reactive with alcohols. The coating materials are compatible and withstand for a long duration. These coatings should also fill the spout and filler pipes. This area is attacked by alcohol fuels.

2.7 Fuel Supply Assembly

Fuel tube bundles are another important part of the engine by which fuel is transported to or from the engine. It includes the feed line, the return line, and any other component attached to the fuel pipe bundle. These components are fuel composition sensors, liquid pressure sensors, fuel filters, and quick connect. These components are made of austenitic stainless steel, and also some of them are of made of carbon steel coated with anti-corrosion materials. The small amount of other materials used to the components affects the components when alcohol fuels are used. There may be a chance of corrosion by using alcohol, if interior part of the tube is not taken care by applying appropriate coatings. Thus the interior parts become an issue of corrosion origination and damage the materials. The coating materials may be nickel or zinc-alloy based.

2.8 Fuel Pump Module

Fuel pumps are made of many materials. Fuel pump contains many components such as float arms, springs, fuel filters, pressure regulators, electrical terminals, flanges and polymer flanges filled with metals. Metals used in fuel pump assembly are coated steel, stainless steel, aluminum, copper, silver, gold, palladium, and platinum. Design details and material selection are necessary for the application of alcohol as an alternative fuel. The older fuel pump systems are incompatible for alcohol fuel exposure and affect the performance of the system and greatly reduced the life of the component.

The internal component of the fuel pump system is also considered when alcohol fuel is used in the engine as fuel. It contains electrical contact, armature, motor features, and pumping section. Materials used in these components are aluminum, copper, and zinc and these materials are very reactive with alcohols. The electrical devices used to reduce the electronic noise produced by the electric motor of the fuel pump are a major concern by using alcohols and taken care. These components and their joining (solder or weld) and electrical leads should be protected by a coating or enclosing the whole subassembly into an encapsulation. A compatible coating must be applied to the armature and points where they are attached. The copper commutator face used in brush type motor is replaced with the carbon to avoid degradation in alternator by use alcohol fuels. Another option is the selection of brushless motor for fuel pump systems. Another part of the fuel pump system is pumping section, which is to be studied. Pumping section material is an aluminum plate which is used in turbine style pumping and protected. The application of ionized aluminum which is sealed has no issue degradation with the application of alcohols. Unprotected aluminum causes premature wear and degradation when exposed to alcohol. The old type of pump design (vane style or gear style with unprotected steel pumping section) is modified for the higher durability with the application of alcohol fuels (Galante-Fox et al. 2007).

Materials for fuel filter and pressure regulators are major challenges for the use of alcohol fuel in the engine. The moisture present in the alcohol fuel is accumulating in the fuel filter when the fuel pump system is inactive. There is a generation of the static field in the presence of fuel which is electrically conductive cause corrosion of components. The corrosion of the pressure regulator is avoided by using a good quality seal, and pressure is maintained when the pump is on. Fuel pressure regulator and fuel filters are made of austenitic stainless steel to avoid corrosion. The old design materials of filters and regulator are stainless steel and zinc coated carbon steel respectively which is changed according to the alcohols fuel compatible materials. The other components of fuel pump systems materials are changed according to alcohol compatible materials. These components are springs, guide rods, float arms, electrical terminals, wires, and level sensor contacts and their compatibility with alcohol fuel must be reviewed. These parts are generally made of austenitic steel and wires and terminals are protected from alcohol by insulation and tin plating, respectively. The terminal of level sensors is also taken care as a small electrical load generates stress on terminals and causes corrosion when exposing to alcohol (Matthias and Thomas 2009). Other challenges of a modern fuel pump are high voltage electrical interface. Improperly timed motor cause the wear of carbon brushes which in contact with carbon or copper commutator of the armature. Thus electrical connector design is such that electrical cross-talk should be avoided which lead to terminal corrosion by application of alcohol fuel.

2.9 Fuel Rails and Injectors

Most of the fuels contacting parts are made of stainless steel. These components which handle fuels are fuel injectors and fuel rails. Generally, stainless steel is corrosion resistant but not corrosion proof with alcohol as fuels (Shifler2009; Scholz and Ellermeier 2006). Presence of chloride contamination, which is easily soluble in alcohol may cause the corrosion and at stressed point cause the corrosion cracking. Fuel delivery components experience higher stress in spark ignited direct injection technology than conventional port injection due to higher fuel pressure. Many researchers have studied that aluminum components exposed to alcohol are corroded significantly (Yuen et al. 2010; Priyanto 2017). Thus the improper design of material and aluminum components which are direct contact with alcohol exhibited problem and should be taken care of. Aluminum fuel delivery pipes are corroded in the presence of moisture in alcohol fuels. The rust of corroded components may plug the injectors and causes the rough running of the engine. The continuous operation of the engine, the corrosion of fuel rail increased, and pin holes may develop resulting leakage of fuel rails. The dry corrosion is due to the reaction between aluminum and alcohol. Thus alcohols may cause dry corrosion as well as wet corrosion of the fuel components so, the material robustness is optimized.

2.10 Engine Valve and Valve Seat

There is a significant amount of valve wear and increase of insert of the valve seat due to the application of alcohols as a substitute for gasoline. So the appropriate materials for the valve train design and materials are selected to meet the end-user life expectations. Various parameters are taken into account for the selection of materials. These parameters are machinability, wear resistance, tribo-oxidative wear, and corrosion of the metal materials and also have a higher cost. Several paths have been used to make the valve seat. These paths involve higher tool steel percentage in powder metal mixture and inclusion of powder metal components like molybdenum and cobalt in powder metal technology of sintering. With the use of alcohol, there is a possibility of wear of valve face and valve seat and lead to an engine misfire.

3 Methanol-Fueled Engines

Methanol is used in an internal combustion engine as fuel in many ways such as direct injection of methanol in the combustion chamber or by mixing with conventional fuel. Mixing of methanol with convention fuels is taken place inside combustion chamber or outside combustion chamber. Blending of methanol with diesel or gasoline is performed for outside mixing, however methanol is injected in port fuel injection.

3.1 Methanol Application in Spark Ignition Engine

As methanol is resistance to auto-ignition due to lower in-cylinder temperature, and also the higher auto-ignition temperature cause resistance to knocking. However, properties of methanol in terms of output power, efficiency, and emission are similar to spark ignited engine. Methanol is suitable fuel for spark ignition engines as it has high heat of vaporization and also high autoignition resistance Table 3.1. It can be used as a blend with gasoline or in pure form. Methanol can also be used as an octane booster for gasoline to avoid the knocking as it has a high octane number and also lowers the combustion temperature. Engine modification for a lower percentage of methanol as blend in spark ignition engine operation is not necessary. Caution is required for using the splash blending of methanol with gasoline as the pump is not tailored for methanol in the fuel blend causes higher volatility and resulting fuel evaporation. The volumetric content of energy is necessary for the design of the fuel injection system and fuel tank. As the methanol volumetric content of energy is half of the gasoline, so injection duration of methanol fuel should be nearly double of the gasoline for the same amount of power generation thus suitable injector design is required. For the similar driving condition as the gasoline vehicle, the larger fuel tank is required for methanol. As methanol is resistance to auto-ignition due to lower in-cylinder temperature, and also the higher autoignition temperature cause resistance to knocking.

3.2 Methanol Application in Compression Ignition Engine

Compression ignition engines are most commercially used, so there is a very strong interest of using methanol in compression ignition engine. Methanol has very low cetane numbers, which indicate the autoignibility of methanol. As the methanol has high autoignition resistance, it is used in diesel engine application and requires major modification in the engine. Use of methanol/diesel mixture requires co-solvent or emulsifier agent as methanol diesel do not mix and also methanol fraction is limited. A simultaneously higher fraction of methanol reduces the volumetric energy content and difficult to maintain the same power applying the same injectors. Lubricity of fuel is also decreased and need some lubricating additives. Dual fuel mode is very common, where diesel and methanol are injected in engine separately. Methanol applications in large diesel engines are as dual fuel mode. Recently dual fuel mode is used in many large ships engines where methanol is injected separately, and diesel is used as a source of ignition. This application required modification in the engine cylinder heads and the fuel injection system. The fuel injection system contains separate direct injection methanol injectors or custom built injectors, which allows injecting diesel and methanol to the cylinder (Bünger et al. 2012). In the dual fuel application in an engine, port fuel injection is used for the injection of methanol, and it improves the emissions. The glow plug is used as an ignition source in place of pilot fuel injection for methanol-fueled compression ignition engine (Verhelst and Wallner 2009). Recently compression ignition research engine fueled with methanol is running in the homogeneous compression ignition (HCCI) mode and partially premixed combustion (PPC) mode (Shamun et al. 2016, 2017). These type of combustion mode reduce the soot formation. Most recent research of methanol used in a compression ignition engine is reactivity control compression ignition, which reduced the NOx and soot simultaneously by complete combustion of fuel (Dempsey et al. 2013).

3.3 Methanol-Fueled Engine Design Customisation

There is a requirement of changes or modifications of the hardware of engines or vehicles due to corrosiveness of methanol and its blends with gasoline or diesel. All the vehicle engines running by using a low percentage of methanol (methanol less than 5%) need not require any modification. Low concentration of methanol increases the vapor pressure of gasoline and requires changing the formulation of the base fuel gasoline. Older vehicles cause the problems even at the low level of methanol blends with conventional fuel because methanol acts as a solvent and dissolve the deposits in the fuel system and blockages the down the line. For the use of a high percentage of methanol or neat methanol, there is a requirement of changing of engine hardware materials. Fuel additives are required to improved lubricity and anti corrosivity property to protect the metals (Xiang 2015).

IC engines running on methanol are specially designed to overcome the corrosiveness of the fuel. The engine components design and materials are customized according to the methanol as a fuel in the engine. The new materials such as polyethylene or stainless steel and chrome or nickel plating are selected for fuel tank and fuel system, respectively. The port fuel injection technique is best for the methanol to achieve better fuel air mixing and vaporization.

3.4 Cold Start Challenges

There is a problem of cold start of a high percentage of methanol in gasoline. For the successful cold start of methanol blended gasoline engine, the combustible mixture of fuel-air is required and should generate sufficient heat to retain engine running (Yuen et al. 2010; Pearson et al. 2012). Solutions for the cold start and minimize the addition systems requirement by optimizing the following components:

Engine Block: Cold starts problem can be reduced by heating the engine intake and block electrically (Bergstrom et al. 2007; Cowart et al. 1995).

Injector: Startability issues of an engine can also be suppressed by heating injectors individually or fuel rail to enhance the vapor formation of methanol (Kabasin et al. 2009). Second option to enhance vaporization is by heating the intake air (Gong et al. 2011; Colpin et al. 2009). Another way, the injection pressure is enhanced to improve the vaporization and atomization of spray.

Valve: Some researchers have investigated the valve timing effect on the cold startability and observe that both exhaust and intake valve opening and closing would affect the cold startabilty (Colpin et al. 2009; Nakata et al. 2006).

Ignition: Ignition timing adaptation is very important for the cold start. Sometimes multiple sparks are used. Some researchers have proposed the plasma jet spark to enhance startability (Markel and Bailey 1998).

Direct Injection: Late injection and stratification are an effective way of improving cold start performance. Siewart et al. (1987) investigated cold start successfully at the temperature less than −29 °C for methanol (Marriott et al. 2009).

3.5 Fueling Systems Customisation and Ignition

As the volumetric energy content of methanol is lower than the conventional fuel, so injectors and fuel pumps of methanol-fueled engines should be with increased flow rate to achieve peak power. Fuel pumps and injectors have the material compatibility issue with methanol (Galante-Fox et al. 2007; Priyanto 2017).

Methanol has been easily pre-ignited due to the presence of a hot spot in the combustion chamber. Methanol generates no soot in flames causes the overheating of ignition source like spark plug electrode (Kalghatgi and Bradley 2012). The temperature of the electrode is in between 700 and 925 °C and suitable for gasoline. So for reducing the electrode temperature, a low heat grade spark plug is needed (Kabasin et al. 2009). Suga et al. (1989) investigated the pre-ignition tendency using various spark plugs with similar heating range. It was observed that spark plugs with platinum tipped electrodes were prone to pre-ignition. Many other researchers had also investigated the spark plug electrode of noble metal with high pre-ignition temperature tendency (Naegeli et al. 1997; Yuen et al. 2010).

3.6 Engine Cylinder Head Modification for Methanol

Methanol has very high heat of vaporization, which causes the cooling of intake port and leads to a low temperature of intake. This starts increasing thermo-mechanical stress in the head, and its measurement is necessary (Bergstrom et al. 2007). Valves seat inserts and valve suffer from higher wear during methanol operation due to non-lubricating nature of alcohols and produces lesser lubricating soot. Inlet valve experience increased contact forces due to enhance combustion pressure and thermal shocks (Bergstrom et al. 2007). Thus selected materials for these components are with higher hardness and chrome content (Giroldo et al. 2005; Bergstrom et al. 2007).

Ignition retard is not necessary for the knock suppression at peak power as methanol is knocked resistance but lead to higher peak cylinder pressure. Thus ignition retard is necessary to suppress peak pressure within the allowable limit. Thus methanol engine should have variable valve timing systems with wider timing window for the advantages of internal exhaust gas recirculation rates.

3.7 Vehicle Adaptation and Durability

As the volumetric energy density of methanol is much lower than gasoline and diesel, the larger size fuel tank is required for the same driving range. Thus, the additional weight has to carry the vehicle when it fully fueled. Formaldehyde (HCHO) emission from the methanol-fueled engine is increased as compared to gasoline and concern as these emissions are currently unregulated. It is a human carcinogen and plays a very crucial role in tropospheric photochemistry (Wei et al. 2009). Formaldehyde is an intermediate product during combustion at a temperature around 1000 K (Svensson et al. 2016) and leads to formaldehyde emission in case of port fuel injection (PFI) in which methanol goes to crevices and escapes during the expansion stroke. But in case of direct injection of methanol formaldehyde emission is minimized. For methanol application in the engine, there should be specific after treatment catalyst formulation to reduce the formaldehyde emissions.

Engine durability is the proper functioning and reliability of an engine over a long period of time. Durability of existing engine is major technical hurdle for application of methanol as fuel. This is because of corrosive nature of methanol which causes corrosion and wear of engine components. The durability of methanol fuelled engines is improved by engine modifications like using new materials and design features of the engine. These modifications in the engine components are fuel supply systems, fuel mixture delivery, engine cylinder liner, piston rings and engine oil formulations (Ernst and Pefley 1983).

4 Summary

This chapter provides a comprehensive review of materials compatibility for the methanol-fueled engines and design of engine components. The above study covers all the aspect of material compatibility and design are discussed, which are as follows:

  • Material compatibility of automotive engines and material selection for that

  • Wear and corrosion of engine component due to methanol and prevention

  • The storage of methanol fuel and their handling

  • Design of engine components and subsystem compatible with methanol

The reality of the study is that automotive engineers have to develop the engine for the methanol application in advance for their use. The consumers need transparency about legality of fuel, economy, and durability of engines. They also keen for the easy modification of the engine for methanol.