1. Advantages of Alcohol over gasoline
• Renewable in nature
• Higher Octane rating
• Higher power due to better volumetric efficiency
• Higher thermal efficiency due to higher HUCR
• Produces less emissions compared to gasoline.
2. Limitations of Alcohol over gasoline
• Lesser Calorific Value and Higher cost.
• Combustion of alcohols produces aldehydes in the exhaust which are harmful.
• Water absorption- hence metal corrosion problem
• Chemical attack on plastic components in direct contact
• Lower overall system efficiency- production to utilization.
• Almost invisible flames considered dangerous when handling fuel.
• Strong odor of the fuel.
• Storage tank flammability due to air leak into the storage tanks.
• Utilization of alcohol blend for automobiles requires proper
monitoring, accounting and caution in handling stations.
• Utmost care should be taken to store the alcohol and its blends to
keep away from moisture.
• Adequate steps should be taken to double the alcohol production to
meet the requirement.
• Alcohol burns at half the speed of the engine.
• Latent heat of vaporization is much greater – cold starting problem.
Utilization of alcohol in Diesel engines
• Blend of moisture free alcohol in Diesel (
Upto 20%) can be used
• Dual fuel injection.
Merits of Hydrogen
Hydrogen has the fastest burning velocity which causes rapid combustion and
hence high engine speed, thereby improving the specific output.
It has an excellent lean burning ability which improves its thermal efficiency.
It has a high Octane Number, which enables higher CR to be used with the
associated higher imep and higher energy conversion efficiency.
It has a high self ignition temperature (581ºC compared to 450ºC for gasoline or
466ºC for propane and 534ºC for methane) which makes it highly knock resistant.
When it burns in air it produces steam and the exhaust is devoid of CO, CO2, SO2,
smoke and Carcinogens. The only expected pollutant is NOx which can be easily
controlled by lean burning or by EGR technique.
Tasteless, odourless and non-toxic by itself, hydrogen gives out just clean energy
producing steam, thereby maintaining the Nature’s balance of water in the
It is highly combustible, requiring very little energy (1/12 of gasoline) to ignite it.
(0.02 mJ compared to 0.25 mJ for gasoline and propane and 0.3 mJ for methane
under similar laboratory test conditions).
It has a very high calorific value on mass basis.
PRODUCTION OF HYDROGEN
• Hydrogen can be produced by several methods. 65% of the total production
of hydrogen in the world is by catalytic steam reforming of methane or
naptha, 25% by partial oxidation of heavy oils, 7% by water gas reaction
from coal/coke and 3% by electrolysis of water.
• Direct thermal splitting of H2O (at 3000ºC) using solar focusing collectors,
thermo-chemical splitting of H2O (at 850ºC) using FeCl2 or CrCl2,
modified photosynthetic reactions in green plants and algae using specific
enzymes etc. are some of the techniques under consideration and
development to produce hydrogen.
DE-MERITS OF HYDROGEN
• Its high combustibility can cause fire hazards and inlet back fire. This requires flame traps,
flash back arresters and crank case ventilation to prevent explosions due to blow-by
• Due to its very low density (0.09 kg/m³ for the gas) it has a very low volumetric energy density
and hence on-board storage requires a large volume for a given mass.
• Due to complexity and cost of cryogenic liquid hydrogen storage, carrying hydrogen on board
in a vehicle is a challenging task. One of the acceptable solutions is storage in the form of
metal hydrides, which, unfortunately, can hold only about 2 to 8% by mass of hydrogen in it.
• Hydrogen is very expensive and its production is highly energy intensive.
Carburetion or valve controlled flow into the intake manifold directly from
hydrogen cylinder or hydrid storage.
Manifold hydrogen gas injection.
Direct in-cylinder injection (Gas or Liquid)
ON-BOARD STORAGE OF HYDROGEN
Compressed hydrogen gas storage in high
Hydrogen storage in the liquid form
Comparison of typical hydrogen storage systems for equal energy storage
Mass of fuel in kg
Mass of container +
Hydrogen gas at
Metal Hydride: Mg-Ni 310
Hydrogen as an alternative fuel -conclusion
Technical feasibility of hydrogen as a renewable alternative to petroleum fuels has been
successfully demonstrated by experiments in the laboratory as well as on the road. However,
before hydrogen can be considered for wide use in automobiles further research efforts are
required in the following areas-
Production of hydrogen at an affordable cost
On-board storage of hydrogen with improved power to weight ratio
Safe methods to prevent fire hazards during operation and due to accidents
Analysis of hydrogen supply system with computerized control of mixture ratio in response
to drive commands and exhaust emission levels
Performance studies on all-weather and altitude operation including extreme cold starting