methanol.pdf

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Technical Review

Methanol as a fuel for spark ignition engines: a review and analysis

A Kowalewicz, PhD, DSc Radom Technical University, Poland

A review and analysis of recent lilerature data on the use of methanol as an alternative fuel for internal combustion engines have been performed. The properties of methanol have been analysed from the point of view of its application to spark ignition (SI ) and compression ignition (CI ) engines. From this analysis it may be concluded that fewer modifications to the engine are expected when melhanol is used in S1 engines than in CI engines. Neat methanol is the most suitable, because all the positive properties of methanol as a fuel can be utilized. In the case of SI engines, only minor modijications of the fuel system and/or addition of ignition improver to the fuel are required. Use of methanol-gasoline blends of up to 15 per cent methanol (by volume) and diesel oil-methanol blends of up to 20 per cent methanol require only minor engine modifications. However, miscibility of methanol and conventional fuels is poor; in order to avoid fuel separation, mixtures of these fuels require fuel additives. Methanol engines burn cleaner and more efficiently, but have higher emissions of aldehydes, which increase with increasing mileage of the vehicle. In the presence of an oxidation catalyst unburned melhanol can be converted to formaldehyde and simultaneously nitrous oxide to nitrogen dioxide. The advantoge of engine fuelling with reformed methanol (CO + H,) is shown. The reasons for better eficiency, performance and less emissions (except of aldehydes) of methanol-fuelled SI engines in comparison with gasoline- and diesel oil-fuelled engines respectively have been analysed. Technical aspects of using methanol as an automotive fuel that have not yet been satisfactorily solved are pointed out. The feasibility of the widespread use of methanol QS a transportation fuel for SI engines is discussed from technical, economic and ecological points of view. The need for further research and development work on problems related to methanol as a fuel for SI engines is also discussed.

1 INTRODUCTION

Interest in methanol as an alternative fuel for internal combustion (IC) engines started in the early 1970s due to considerable increase in petroleum fuel prices in the world markets. Methanol, however, had been recog- nixed earlier as a high-performance fuel for racing cars, on account of its high resistance to knocking combustion (1). In the 1980s the interest in alternative fuels fell due to a surplus of petroleum fuels, but it is now rising again mainly due to ecological reasons: it burns cleaner, that is the emission of solid particulates as well as toxic components is lower in methanol in comparison with petroleum fuels. Moreover, methanol fabri- cated from crops or waste does not contribute to the greenhouse effect and, thus, to global warming. In many countries research and development work on methanol as a fuel for IC engines is sponsored by their governments and/or UNIDO, including some West European countries, India and China. Novel control techniques of IC engines have created better opportunities to utilize potential features of methanol as a fuel, especially from thc point of view of reduced environmental pollution.

The objective of this article is to review the main problems connected with using methanol fuels (including neat methanol) in 1C engines, in particular:

(a) to compare the properties of methanol and conventional petroleum fuels and mixtures of these fuels with air from the point of view of application in IC engines ;

(b) to describe modifications of combustion systems of conventional SI engines needed to enable the use of methanol fuels;

The MS wus received on 18 July 1991 and was accepted for publication un 18 September 1992.

(c) to review and analyse the main recent results of research and development work on application of methanol fuels to SI engines;

(d) to discuss problems that demand further research and development work;

(e) to discuss the feasibility of widespread use of methanol as a transportation fuel from technical, economic and ecological points of view.

2 FABRICATION OF METHANOL AND ITS FEATURES AS A FUEL FOR IC EKGINES

2.1 Fabrication of methanol

The raw materials for methanol production are coal and remote natural gas; these may all be carbon containing materials, that is residual oil, shale, peat, tar sands and waste (2). Methanol is produced in two steps. In the first step synthetic gas (H, + CO) is produced by reaction of gasified raw material with steam at high temperature. In the second step methanol is produced from compressed (50-200 bar) synthetic gas by a catalytic process (copper-based catalyst). The energetic eficiency of methanol production is as follows (3):

(a) from natural gas (b) from coal (c) from biomass

and is higher than that of gasoline (MTG process and Fischer-Tropsch method) and of diesel oil (Fischer- Tropsch method). The costs of methanol (produced from coal) and gasoline in the United States and Germany are nearly the same; that of methanol is a little higher but could be lowered by mass production.

60-65 per cent 47-52 per cent 42-52 per cent

2.2 Properties of methanol as a fuel for IC engines

The chemical content of methanol, gasoline and diesel oil is given in Table 1. Due to the fact that 50 per cent

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44 A KOWALEWICZ

Table 1 Chemical content of methanol and conventional fuels

Mass content Yo

Kind of fuel Carbon Hydrogen Oxygen Sulphur ~

- Methanol 37.5 12.5 50 Gasoline 85.0 15.0 ~

0.5 Diesel oil 87.0 12.5 -

-

(mass) of methanol content is oxygen, the stoichiometric amount of air necessary for methanol combustion is smaller and its calorific value is lower in comparison with petroleum fuels. The properties of methanol and conventional fuels are given in Table 2. From these data the following conclusions regarding methanol as an automotive fuel may be drawn:

Bene$ts 1 . High resistance to knocking combustion (high octane

number), due to which higher compression ratios may be applied, resulting in higher efficiency

2. Cleaner (soot-free) combustion 3. Lower lean flammability limit, resulting in the possi-

bility of lean mixture application and, consequently, better economy and lower emissions of NO,, HC and CO

4. Higher heat of evaporation, resulting in a higher temperature drop in the Venturi nozzle of the carburettor and therefore higher volumetric efficiency

5. Lower combustion temperature, resulting in lower NO, emission

6. Higher volatility, resulting in better distribution among cylinders of air-fuel ratios and mass of fuel per cycle of multi-cylinder carburettor engines

Shortcomings 1. Poor self-ignition properties (long ignition delay) 2. Poor miscibility with mineral fuels (especially with

diesel oil) in the presence of water 3. Difficult starting of cold engine 4. Corrosion and chemical degradation of materials

By analysing the properties of methanol it can be concluded that methanol is a good fuel for IC engines, especially SI engines. Its application to SI engines presents important problems:

1. The combustion system of conventional engines need to be modified.

2. Fuel additives are required when neat methanol is used.

3. Some properties of methanol give it potential advantages as an automotive fuel, that is improved engine performance.

3 METHANOL FUELENGINE CONCEPTS

3.1 Fuelling with neat methanol

From a technical point of view, neat methanol may be a very good fuel for SI engines, especially in areas with a warm climate. However, the engine fuel system needs to be modified due to the lower calorific value and smaller stoichiometric air-fuel ratio of methanol in comparison with gasoline. A better engine efficiency may be expected, mainly due to :

(a) application of a higher compression ratio (CR), (b) possibility of operation on a leaner mixture, (c) recovery of the latent heat of evaporation in the

The efficiency of an optimized methanol-fuelled engine may reach 40 per cent (3).

Concepts of fuel supply systems of an SI engine are shown in Table 3. A very interesting gas methanol supply system with heat recovery in an SI engine can be found in a Mercedes-Benz engine (4). In cold climate countries it is necessary to improve cold start by pro- viding :

(a) a heating inlet duct and/or (b) an ignition improver, that is an additive added to

heat balance of the engine (4).

liquid methanol. - 5. Evaporation in fuel lines (vapour locks) 6. Poor lubrication properties resulting from low vis-

7. Degradation of oil lubrication properties

The advantages of application of neat methanol to SI engines are (with the exception of those mentioned above) better engine efficiency and lower emissions of CO, HC and NO, (5). However, emission of aldehydes

cosity

Table 2 Properties of neat methanol, gasoline and diesel oil

ProDertv Unit of Diesel measure Methanol Gasoline oil

Density (20°C) Lower calorific value

Lower calorific value of stoichiometric mixture with air

Stoichiometric air-fuel ratio Heat of vaporization Boiling temperature Ignition temperature Vapour pressure (20°C) Lean boundary air-fuel

Viscosity (20°C) Octane number

equivalence ratio

MON RON

Cetane number Maximum flame velocity

kg air/kg fuel

"C K kPa

kJ/kg

-

CP

79 1 19.5 15.78

3175

6.4 1104

65 743

37 1.9

0.6

92 110

3 55

740 44.0 32.5

3439

14.9 330

773 30-225

60-90 1.16

0.42

84 92 14 40

840 42.5 35.7

3475

14.6 250 170-320 493 - 0.975

3.3

~

45-55 -

Part D: Journal of Automobile Engineering Q IMechE 1993

METHANOL AS A FUEL FOR SPARK IGNITION ENGINES: A REVIEW AND ANALYSIS 45

Table 3 Fuel supply systems for neat methanol

Fuel system Necessary modification

Carburettor Injection system Gas carburettor

Larger cross-sectional area of fuel nozzle Larger cross-sectional area of injector nozzle For evaporation of liquid methanol a heating

system and a special fuel supply system with reductor should be supplied

is higher, but they can be neutralized by a catalytic process.

3.2 Fuelling with gasoline and methanol

3.2.1 Introduction

According to many authorities [for example see references (3) and (6)], the introduction of methanol as automotive fuel should take place in two steps. The first involves the use of methanol together with gasoline, the second one, neat methanol. The first involves the use of methanol together with gasoline, the second one, neat methanol. The first is useful because it enables the favourable features of methanol to be utilized while omitting the shortcomings of its application as a straight fuel. The concepts of SI engines fuelled with methanol and gasoline and corresponding engine modifications are shown in Table 4.

3.2.2 Fuelling with gasoline-methanol blends (methanol

Problems related to fuelling engines with gasoline- methanol blends (methanol fuels) are shown in Table 5. The most important is the problem of phase separation, which can be solved with solubility improvers added to methanol fuel. Many experiments have been performed in the United States and European countries [for

fuel)

‘Table 4 Fuel system and engine modifications for methanol- gasoline application

Fuel systems: Carburettor system

Injection system - Two separate carburettors

(+solubility improver) ---+ or Fuelling with blends

Dual fuel system

Engine modifications : (stratified charge)

{

Tuning of carburettor Adaptation of cold start-up and warm-up settings Modification of carburettor fuel system to avoid vapour locks Changing materials in fuel system

Table 5 Problems related to application of methanol- gasoline blends and possible solutions (4)

Problems Solutions

Stability of blend Additives preventing phase

‘Dry’ handling (phase separation) separation (solubility improvers)

Insufficient resistance of Anti-corrosive additives structural materials to methanol corrosion

Higher volatility at the

Higher fuel mass-flow

Adaptation of components of

Adaptation of cross-sectional areas

beginning of evaporation gasoline

intensity

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of nozzles of fuel system

example see references (3) and (5)] from which the following results may be drawn:

1. No modifications and no additives are required for mixtures up to 2-3 per cent by volume of methanol

2. When the content of methanol is higher than 5 per cent it is necessary to change the materials of some parts of the fuel system.

3. Fuelling with gasoline-methanol blends of up to 15 per cent methanol (M15) requires only minor modification of the fuel system (mainly enlargement of the fuel nozzles).

Many experiments have been carried out on gasoline-methanol blends (especially M 15) used in SI engines. The following changes to the engine were performed :

1. Fuel nozzles of the carburettor were enlarged in order to adjust the air-fuel ratio to the stoichiometric value of the actual blend.

2. The mixture was heated before it entered the engine at cold start.

3. The carburettor and fuel line were modified in order to avoid vapour locks and damage to some of the parts (plastic and rubber, especially) as a result of corrosion and material degradation.

Ignition improvers were necessary in all cases as cold- starting aids, especially in cold climates. In order to avoid phase separation of methanol-gasoline blends, additives were also added.

(W.

3.2.3 Dual fuelling

The problem of phase separation of blends does not apply when gasoline and methanol are added separ- ately. Two separate fuel systems are then required. In this case, however, CR may be raised, resulting in higher engine eficiency.

3.3 Engine efficiency and emissions

From a comparison of engines fuelled with neat methanol, methanol blends and neat gasoline, the following conclusions may be drawn (3, 5, 7). In the case of the methanol-fuelled engine, in the whole range of speed and load:

1. The power of the engine is higher (Fig. 1). 2. The overall engine efficiency is higher (Fig. 2). 3. The emission of NO, and HC is lower (Figs 3 and 4

4. The emission of CO is comparable (7). 5. The emission of aldehydes is higher (7).

respectively).

3.4 Lean mixture operation and turbocharging When the engine operates with lean methanol-gasoline blends, peak combustion temperatures are lower than for a stoichiometric mixture and therc is an increase of thermal efficiency, due to:

(a) reduced pumping losses, (b) reduced cooling losses, (c) greater specific heat ratio of leaner charge, (d) reduced dissociation losses.

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Operation p limit

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0 0.9 1.0 1.1 1.2 1.3 1.4 1.5 Air-fuel excess ratio I

Fig. 1 Mean effective pressure (m.e.p.) versus air excess ratio A for a one-cylinder SI engine fuelled with methanol, M15 fuel and gasoline (5)

Also NO, emission is reduced due to :

(a) lower maximal temperature of combustion, (b) a higher mixture air-fuel ratio and a reduction of

the emission of CO and HC due to reduced cooling losses.

However, the emission of aldehydes (which will be discussed in the next section) increases considerably with leaning the mixture. However, the leaner the mixture, the lower the NO, emission, thus reducing the need to use NO reduction catalyst by keeping NO, at the same level as the NO catalyst and the mixture air- fuel ratio close to the stoichiometric mixture (A 5 1).

0.35

r” 0.30

Methanol

# * 1 x CR = 14.0

.

\ * \ < \ &

0.20 0.251 0.8 1 .0 1 .2 1.4

Air-fuel excess ratio I

Fig. 2 Overall efficiency of a four-cylinder SI engine fuelled with methanol or gasoline versus air excess ratio 1 for different CRs (5)

Part D: Journal of Automobile Engineering

Air-fuel excess ratio A

Fig. 3 NO, emission of a four-cylinder SI engine fuelled with gasoline, methanol and M15 fuel versus air excess ratio d (5)

According to reference (S), increasing engine efficiency by 10-15 per cent is possible with lean combustion systems without increasing NO, emission over that of the stoichiometric mixture. The lean limit of the fuel-air ratio depends on the methanol content in the methanol-gasoline blend. Yamaguchi and Sasayama (7) state that this dependence is linear: the higher the methanol content, the leaner the mixture at the flammability limit. From experiments performed by them it may be concluded that emissions of engines fuelled with gasoline and with methanol blend are comparable, though the efficiency of the methanol engine is higher. The best results may be obtained when the lean-burn engine is turbocharged. Increasing the inlet pressure results in a reduction in the shortcomings of the influence of lean operation on combustion, that is the ignition delay time and time of combustion decrease, both of which tend to become elongated with leaning the mixture.

Fundamental research on this problem has been performed by Pannone and Johnson (8). From these experiments the following results have been obtained:

Air-fuel excess ratio A Fig. 4 HC emission of a four-cylinder SI engine fuelled with

gasoline, methanol and M15 fuel versus air excess ratio A (5)

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Vehicle miles x 10'

Fig. 5 Engine-out and catalyst-out formaldehyde emission and catalyst efli- ciency versus vehicle mileage accumulation. Aldehyde emission is measured according to the Japanese eleven-stage test (12)

1. As air excess of the mixture 1 increases net efficiency of the engine generally increases, especially with an increase in inlet pressure at a constant power level.

2. NO, emission reaches a maximum at 1 = 1.05-1.10 and decreases with an increase in 3, at either richer or leaner mixtures. For 1 = constant, NO, increases with an increase in inlet pressure.

3. CO emission reaches a maximum at 1 x 1.0 and then decreases sharply with an increase in A, reaching a minimum at 1 % 1.2. For 1 > 1.3, CO decreases with an increase in inlet pressure.

4. Unburned fuel emission decreases with an increase in 1, reaches a minimum at 1 x 1.1 and then increases. The higher the inlet pressure at 1 = constant, the lower the unburnt fuel emission.

5. Aldehyde emission increases with 1 and then reaches a maximum at 1 = 1.5. Beyond 1 > 1.5 aldehyde emission drops with inlet pressure.

From urban driving modes performed on a test-stand by Bob-Manuel (9) for a turbocharged engine it was found that the methanol-fuelled engine fulfils the ECE Regulation 15 standards with better results than the liquefied petroleum gas (LPG)-fuelled engine. Similar results were obtained in references (10) and (11).

3.5 Aldehyde emission In comparison with a gasoline-fuelled engine the aldehyde emission from a methanol-fuelled engine is considerably higher. Two interesting phenomena have been observed (12):

1. Aldehyde emission increases with engine mileage accumulation (Fig. 5).

2. NO, emission promotes methanol oxidation in the catalyst, resulting in increasing catalyst-out formaldehyde emission (Fig. 6).

The first phenomenon can be explained as follows. The higher the mileage accumulation of the engine, the greater the quantity of deposits on the cylinder head @ IMechE 1993

and piston upper surface (originating from the engine oil). These deposits promote the formation of formaldehyde.

The second phenomenon is caused by methanol oxidation and can be described by the following chemical reactions in the catalyst:

N O + H O z - + N O , + O H

CH,OH + OH .+ CH,OH + H,O

CH,OH + 0, + CHOH + HO,

Not all unburned methanol can be converted to formaldehyde. According to reference (12), at most only about 4 per cent of the feed methanol can be converted to formaldehyde. However, the peak values of formaldehyde formed during methanol oxidation increase for deactivated catalyst in comparison with new catalyst. The highest methanol oxidation activity and lowest formaldehyde yield are shown by platinum and palla-

Japanese 1 1-mode test

0 5.6 6.0 6.4 6.8 1 . 2

Engine-out NO, gitest

Fig. 6 Formaldehyde formation rate measured behind the catalyst versus engine-out NO, emission according to the Japanese eleven-stage emission test (12)

Proc Instn Mech Bngrs Vol 207

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2000 rimin Fuel temperature 20°C I O T A aTDC fuel injection

I I 1 I J -40 -20 TDC 20 40 60 80

Crank angle deg

Fig. 7 Rate of heat release at varied excess air factor and fuel temperature versus crank angle, at n = 2000 r/min (13)

dium catalysts for stoichiometric or slightly rich mixtures. The emission of formaldehyde increases for both rich or lean mixtures.

3.6 Influence of injection timing on combustion and heat

In the case of a timed injection of methanol, combustion processes may undergo a two-stage combustion if the injection is sufficiently early before TDC (top dead centre). In this case Kajitani et al. (13) observed burning of individual droplets in the engine cylinder. They sug- gested that this phenomenon was caused by the higher latent heat of evaporation of methanol in comparison with gasoline, resulting in a longer period of evaporation and ignition of droplets. Due to two-stage combustion, two spikes of heat release rate were observed (Fig. 7). In the first stage, reaction kinetics controlled the combustion: premixed mixture burnt rapidly and a high heat release rate was observed. In the second stage, the diffusion process controlled the combustion: the burning rate was controlled by the evaporation rate of the methanol droplets. The earlier the injection, the more time for fuel vaporization, resulting in elimination of the second stage of the combustion process (13). Leaning the mixture also eliminated the second stage of combustion. Analogously, exhaust gas recirculation (EGR) influenced combustion: for rich mixtures an increase in the EGR ratio could eliminate the second stage of combustion (Fig. 8). For lean mixtures, however, there is no second spike and an increase in the EGR ratio caused only a decrease in the maximum pressure and flattened the curve of the heat release rate.

release rate

3.7 Abnormal combustion Although methanol is resistant to knocking combustion, due to its high octane number, it is prone to preignition, due to its relatively low ignition tem- Part D: Journal of Automobile Engineering

Excess air factor 0.86 I0"CA aTDC injection Fuel temperature T, = 45°C

Crank angle dee

Fig. 8 Rate of heat release with varied EGR content versus crank angle (13)

perature (470°C). The last feature often results in an observed surface ignition prior to and after the moment of normal spark discharge (preignition and postignition respectively). Knocking combustion has not been observed in a rapid compression machine. Neither cool flames nor knocking combustion were expected in a methanol-fuelled engine (14). It is well known that cool flames precede the appearance of knocking combustion, as the initial stage of multi-stage ignition (15). Both kinds of abnormal combustion (that is surface ignition and cool flames) have been investigated in detail by Swain et al. (16). They detected the existence of cool flames (before and after spark ignition) in a methanol- fuelled SI engine when burned residuals were added to methanol-air mixtures. Cool flames can occur at the beginning of the compression stroke, even at light load operation. The frequency of early and late cool flames versus engine speed and load are shown in Figs 9 and 10 respectively. According to Swain's results, cool flames were detected when the intake temperature reached approximately 99°C and their frequency of production increased until a temperature of 113°C was reached. Neither the deposit level nor the spark plug heat range affect the frequency of appearance of cool flames. Cool flames themselves are not dangerous; however, their intermittent production results in changes in the composition of gases in the spark plug gap and combustion space during ignition and pro- duces cycle-by-cycle variations of combustion. It should also be remembered that, under certain circumstances, cool flames may lead to knocking combustion, which is very dangerous for the engine.

In contrast with cool flames, surface ignition is produced by deposits caused by lubrication oil pyrolysing on the hot surfaces of the engine combustion chamber (16). The frequency of appearance of preignition and postignition versus engine speed and load are shown in Figs 11 and 12 respectively. In the case of high speed and load, runaway surface ignition combustion is possible. In this kind of abnormal combustion, a cyclic increase in the rate of pressure rise and an increase of maximum pressure from cycle to cycle is observed

@ IMechE 1993

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Proc Instn Mech Engrs V

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50 A KOWALEWICZ

! SO00

4000

1000

-120 -80 -40 0 40 80 120

deg Crankshaft position

Fig. 13 Cylinder pressure versus crank angle during runaway surface ignition during methanol operation

(Fig. 13). The deposit level on surfaces of the combustion chamber or the spark plug heat range influences the frequency of surface ignition.

According to Haight and Malte (17), the preignition temperature depends on the fuel-air equivalence ratio and spark advance and not on the intake temperature of fresh gases. Preignition was also observed in an SI engine fuelled by methanol-gasoline blend (M85) (18). These results refer to four-stroke engines. However, abnormal combustion has also been observed in a two- stroke SI engine (19).

(16)

4 REMARKS ON FUELLING OF IC ENGINES WITH REFORMED METHANOL

Reforming of methanol can be described by the following chemical (endothermic) reaction :

CH,OH + 2H, + CO

The calorific value of reformed gas is 23.9 MJ/kg, while that of liquid methanol is 20.0 MJ/kg. The reformed gas can be produced on board the vehicle (20) in a reformer after first being vaporized in a vaporizer (Fig. 14). The

rn Methanol tank

Cooler I Methanol

Reformed gas m T (2H2 + C O ) 1 Fuel injection

Fig. 14 Concept of engine fuelling with reformed gaseous methanol (20)

Part D: Journal of Automobile Engineering

reformer is heated by exhaust gases up to temperatures not lower than 300°C. After that the reformed gas is cooled in an air cooler, mixed with air and supplied to the engine. As far as compression ignition (CI) engines are concerned, a pilot injection of diesel oil is necessary for ignition. According to experiments (21), maximum efficiency can be obtained only when 50-65 per cent of the energy fraction of reformed methanol is supplied, the remainder being diesel oil.

5 ANALYSIS AND DISCUSSION

5.1 Features of methanol engine 5.1.1 Efficiency of methanol engine

The first question that arises is why an engine fuelled with methanol (or its fraction) is more efficient than one fuelled with petroleum fuels? According to results of experiments, the efficiency of a methanol-fuelled engine is higher than that of gasoline engines. In the opinion of the present author, this is due to the following reasons :

1. Combustion losses are lower, that is combustion is more complete and more perfect. This has been investigated by Trzaskowski and the author (22). In the opinion of the author this is also the case for C1 engines (with an optimized source of ignition in the case of the methanol engine).

2. Heat losses due to cooling are smaller, because the temperature level in the engine cylinder is lower (23, 24).

3. The combustion period of methanol fuel (or methanol fraction in the fuel) is shorter due to greater flame speed (25) and takes place closer to TDC, which makes the thermodynamic cycle more similar to the Otto cycle.

4. The coefficient of molecular conversion of the charge during combustion for alcohol fuels is higher in comparison with petroleum fuels (due to the presence of atomic oxygen and the greater amount of hydrogen in the molecule). As a result of this, the work done by the expanding gases in the cylinder is greater.

In general, from reviewed work it may be concluded that under the condition of equal fuel energy consumption (energy supplied to the engine with fuel) the higher the fraction of methanol in petroleum fuel, the higher the engine efficiency.

5.1.2 Performance and emission of the methanol engine

Assuming that the energy consumption is the same, torque and power of the engine fuelled with methanol are higher than when the engine is fuelled with petroleum fuels. If the fuel system is not modified to the greater amount of methanol fuel needed, engine performance as well as vehicle acceleration and maximum speed are lower. Torque and power of a methanol engine are higher than a gasoline engine due to

(a) higher thermal efficiency and (b) higher volumetric efficiency of the engine qv.

Emission of NO, from a methanol-fuelled engine is generally lower than when petroleum fuel is used because the maximum temperature of the thermodynamic cycle is lower. These emissions can be lowered even further,

0 IMechE 1993


by leaning the mixture, made especially feasible by increasing the methanol content in the blend. Emission of CO and HC is also lower due to more complete and perfect combustion.

High emissions of aldehydes are an inherent feature of methanol combustion. Emission of aldehydes from a methanol-fuelled engine is much higher than when petroleum fuel is used, therefore making the use of an oxidation catalyst necessary.

Emission of particulates from a methanol-fuelled engine is much lower than when petroleum fuel is used, because methanol is a pure fuel and burns cleaner (due to the chemical structure of the molecule, which con- tains atomic oxygen).

5.1.3 Engineering aspects of the methanol engine

It may be concluded that methanol is a good fuel for SI engines because of its physical and chemical properties (especially its high octane number). However, when methanol-gasoline blends are used in the engine, additives are needed to prevent blend separation when small amounts of water are present. This is the greatest dis- advantage of methanol as a fuel for S1 engines.

5.2 Feasibility of widespread use of methanol as a

5.2.1 Arguments for the use of methanol as a transportation fuel for Si engines

There are two main arguments for introducing methanol to the market as a transportation fuel, especially for cars :

(a) better utilization of the world energy resources and (b) environmental protection due to lower emissions of

In the case of production of methanol from biomass or wood there is additional advantage concerning CO, emission: its circulation is closed, that is CO, produced during the combustion processes and emitted by the engine to the atmosphere is next absorbed by plants. Thus the use of biofuels may prevent the greenhouse effect. For these reason the introduction of methanol to the field of transportation is worthy of consideration.

However, air pollution from methanol production should be taken into consideration. Thermochemical conversion during methanol production from coal and biomass is a threat to air quality (especially in the case of coal, when trace metals are emitted). Methanol production from natural gas is the cleanest.

transportation fuel

pollutants.

5.2.2 Strategy of market penetration by methanol fuel

The first step in introducing methanol as an automotive fuel is to introduce a 5 per cent by volume fraction of methanol to gasoline. No engine modifications would be needed for this fuel. The next step is to introduce a higher fraction of methanol, about 15 per cent by volume. Only minor engine modifications would be needed. The third step would seem to be the introduction to the market of neat methanol engines. At this stage three kinds of methanol fuel would be available on the market for SI engines. 0 IMechE 1993

Table 6 Estimated production costs of gasoline and methanol (2), 1986

cost - $/million Btu

Feedstock Fuel $/gal (million kJ)

Petroleum Gasoline 0.80-1.00 7.00-9.00 ($30/barrel) (6.64-8.53)

Coal Gasoline 1.80-2.60 15.70-22.60

Natural gas Methanol 0.50-0.80 9.10-14.50 (14.88-21.42)

(8.63-13.74) Remote natural gas Methanol 0.40-0.80 7.30-14.50

(6.92-13.74) Coal Methanol 0.80-1.30 14.50-23.60

Wood Methanol 0.80-1.35 14.50-24.50 (13.74-22.37)

(1 3.74-23.22)

This strategy would be feasible if both automotive producers and fuel producers undertook simultaneously to introduce methanol fuel. This scenario could possibly be realized in Western and Middle Europe and in North America. A strategy of fuel production and automotive modification and/or production would have to be supplemented by the establishment of a widespread network of filling stations.

The process of introducing new fuel to the market is very slow for the simple reason that automobiles have a long life [for example in the United States cars have a median life of 11 years and trucks about 14 years (2)]. Moreover, fleet buyers and even individual consumers are conservative. Thus methanol penetration into the transportation fuel market will not occur in a short time. The involvement of governments will be necessary to initiate this process.

5.3 Costs of methanol production The introduction of methanol fuel to the market will be impossible if costs of methanol production are too high. A comparison of American contemporary costs for producing methanol from different kinds of feedstock and for producing gasoline are given in Table 6. It can be seen that the energy cost for methanol produced from natural gas is about 15-60 per cent higher than the energy cost for gasoline made from petroleum. The energy cost for methanol made from other feedstocks (coal, wood) are more than twice higher.

According to reference (3) production costs of energy for methanol and gasoline in the United States are comparable; in Germany methanol production is more expensive than that of gasoline (when available fuel energy data are compared). Mass production of methanol, however, will reduce the costs, because the larger the production, the lower the cost.

6 SUMMARY AND CONCLUSIONS

From this review and analysis the following conclusions may be drawn:

1. In comparison with a petroleum-fuelled engine:

and its emission (except aldehydes) is lower; (a) a methanol-fuelled IC engine is more efficient

Proc Instn Mech Engrs Vol 207

A KOWALEWICZ 52

2.

3.

4.

5.

(b) vehicle acceleration and-in general-drivability with a methanol engine are the same or better, under the condition that energy supplied to the engine is the same;

(c) in general, the higher the content of methanol in the mixture with petroleum fuel, the higher the efficiency of the engine, under the condition that in both cases the value of A is the same.

Generally, the higher the content of methanol in the fuel, the higher the efficiency and the lower the emission of HC, CO and especially NO,. Aldehyde emission, however, increases with an increase in the methanol fraction. The cost of energy production for methanol (from natural gas) is a little higher than the cost of energy production for gasoline, but mass production of methanol would lower this cost. In the case of engine fuelling with fuels containing up to 15 per cent fraction of methanol, no engine modifications (except some minor material substitutions) are required. In the case of fuelling with neat methanol, a modification of the fuel system is required. Further research and development work on methanol application is required to introduce methanol fuel in practice.

Problems demanding further research and develop-

noZogica/ change, 1990 (University of California Press, Berkeley, California).

3 Pischinger, F. Alcohol fuels for automotive engines. Development of transport fuels. Report RTD 6/3, 1990 (FEV-Motorentechnik, Achen, Germany).

4 Bergmann, H. K. A high efficient alcohol vapour aspirating spark- ignition engine with heat recovery. SAE paper 821190, 1982.

5 Lee, W., Konig, A. and Bernhardt, W. Versuche mit Methanol und Methanol-Benzin-Mischkraftsteffen. Report MTZ 5,1976.

6 Lenz, H. P. Application of alternative fuels for I.C. engines. Report UNIDO/I0.516, 1982.

7 Yamaguchi, T. and Sasayama, T. The effect of methanol-gasoline mixing ratio on performance of I.C. engines. SAE paper 900584, 1990.

8 Pannone, G. M. and Johnson, R. T. Methanol as a fuel for a lean turbocharged spark ignition engine. SAE paper 890435, 1989.

9 Bob-Manuel, K. D. H. The use of liquified petroleum gas methanol and unleaded gasoline in a turbocharged spark-ignition engine operating on the simulated ECE-I5 urban cycle. SAE paper 900709, 1990.

10 Yasuda, A., Tsukasaki, T. and Ito, S. Development of second gen- eration methanol lean burn system. SAE paper 892060,1980.

11 McCabe, R. W., King, E. T., Watkins, L. W. H. and Gandhi, H. S. Laboratory and vehicle studies of aldehyde emission from alcohol fuels. SAE technical paper series 900708, 1990.

12 Tsukasaki, Y., et al. Study of mileage related formaldehyde emission from methanol fuelled vehicles. SAE paper 900705, 1990.

13 Kajitani, S., et uf. A timed Fuel-injection spark-ignition engine operated by methanol fuels. SAE paper 900355, 1990.

14 Downs, D., Grifftths, S. T. and Wheeler, R. W. Pre-flame reactions in S.I. engine: the influence of tetraethyl lead and other anti- knocks. J . lnst. Petrol., 1%3,49 (469).

15 Fish. A.. Read. I. A, Affleck. W. S. and Haskell. W. W. The con- I , , I ment work are as follows : trolling role of cool flames in two-stage ignition. Combust. Flame,

1.

2.

3.

4.

5.

6.

1

2

Application of lean mixtures (stratified charge engines) Investigation of abnormal combustion, especially when lean mixtures are applied Application of high-energy spark plugs (plasma plugs), especially to lean mixture engines Fuelling with gaseous methanol, reformed methanol and hydrogen-enriched methanol Improving additives to gasoline-methanol blends to avoid phase separation in the presence of water In the area of catalysts : (a) Optimization of catalysts, especially for neutral-

ization of aldehydes (b) Determination of the limit of the quantity of

NO, concentration that may be converted to formaldehyde

REFERENCES

Kowalewicz, A. Combustion systems of high-speed piston I.C. engines, 1984 (Elsevier, Amsterdam). Sperling, D. New transportation fuels. A strategic approach to tech-

- - February 1969,13,39-49.

16 Swain, M. R., Bianco, J. A. and Swain, M. N. Abnormal combustion in a methanol fuelled engne. SAE paper 892162, 1989.

17 Height 111, W. H. and Make, Ph. C. Characteristics of methanol preignition in a laboratory spark ignition engine. Paper presented at Second Joint Technical Meeting of the Canadian and Western States Sections of the Combustion Institute, Banff, Alberta, Canada, 1990.

18 Maji, S., et al. Abnormal combustion in two-stroke S.I. methanol engine. SAE paper 880174, 1988.

19 Suga, T., Kitajiama, S. and Fuji, S. Preignition phenomena of methanol fuel (M85) by the post-flame technique. SAE paper 892061, 1989.

20 Korematsu, K. and Fukuda, M. Design and road test of new gener- ation methanol vehicle. Int. J. Energy Systems, 1983,3 (2).

21 Korematsu, K., et al. Dual fuelled diesel engine with diesel fuel and reformed methanol. SAE paper 831298, 1983.

22 Trzaskowski, A. Combustion losses of S.I. engine fuelled by methanol-gasoline blend. Diploma work under the direction of Professor A. Kowalewicz, Radom Technical University, 1991.

23 Sobotowski, R. Przyczyny wzrostu mocy silnikbw o Z.I. msilanych metanolem (Reasons of power increase of S.I. methanol engines). Technika Motoryzacyjna 2, 1979.

24 Work done on a methanol-fuelled engine at Engines Department, Radom Technical University, 1991 (not published).

25 Hirano, M., et al. Burning velocities of methanol-air-water gaseous mixtures. Combust. Flume, 1981,40, 341-343.

Part D: Journal of Automobile Engineering Q IMechE 1993

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