1992-09-01

Investigations on the Design and Performance of Two Types of Hot Surface Ignition Engines 921632

Use of methanol and ethanol in conventional diesel engines is associated with problems on account of the high self ignition temperature of these fuels. The Hot Surface Ignition (HSI) method wherein a part of the injected fuel is made to touch an electrically heated hot surface for ignition, is an effective way of utilizing these fuels in conventional diesel engines. In the present work two types of HSI engines, one using a large ceramic base and the other using a conventional glowplug were developed. These engines were tested with methanol, M.spirit (about 90 % methanol and 10 % ethanol) and diesel. The results of performance, fuel economy emissions and combustion parameters including heat release rates for these fuels with both the types of HSI engines are presented.
Diesel engines are commonly used as primemovers in the mass transportation and agricultural sectors because of their high brake thermal efficiency and reliability. On the other hand, the rapid depletion, rising prices, uncertain supplies and ever increasing requirement of petroleum products have forced researchers to find alternative fuels for diesel engines. The concern for a clean environment has given further impetus to this search.
Methanol and ethanol are the most favoured alternative fuels since they can be produced from a wide variety of feedstock including the renewable ones. They also burn without soot. In general, alcohols are excellent spark ignition engine fuels. However, their use in diesel engines is associated with problems on account of their low cetane numbers, low viscocity & poor missibility with diesel in the presence of moisture. Use of neat alcohol in the diesel engine will need a compression ratio of 23:1 for starting and 20:1 for normal running (1). To use neat alcohols in diesel engines at normal compression ratios, ignition assistance in the form a timed spark or a hot surface is needed.
In the Hot Surface Ignition (HSI) engine a part of the injected fuel is made to touch an electrically heated hot surface for ignition. Combustion then follows in the normal way. The proneness of methanol and to a lesser extent ethanol to surface ignite make them ideal fuels for the HSI engine(2). This method has the following advantages over its spark assisted counterpart (3&4):
  1. (a)
    Better ignitability,
  2. (b)
    Possibility to switch off the electrical input at high outputs and
  3. (c)
    Better multifuel capability.
In the present work two types of HSI engines, the first using a Ceramic Hot Surface and the second using a conventional Glowplug were developed. Both the engines were identical except for the ignition source. Experiments were carried out to obtain the performance, fuel economy, emissions and combustion parameters using alcohols and diesel at a compression ratio of 16.9.

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