Page 252 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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236 Automobile mechanical and electrical systems

Figure 2.312 First ethanol vehicle in the UK. (Source: Ford Media)

Figure 2.313 Escape hybrid E85 produced in the USA. (Source: Ford Media)

are also some disadvantages, not least of which is that the cost of production is
high. This is likely to change, however, as their use becomes more widespread
( Figs 2.312 and 2.313 ).

Key fact 2.6 Ignition systems
The purpose of the ignition system is
to supply a spark inside the cylinder, 2.6.1 Ignition overview
near the end of the compression 2.6.1.1 Introduction
stroke, to ignite the compressed
charge of air/fuel vapour. The purpose of the ignition system is to supply a spark inside the cylinder, near
the end of the compression stroke, to ignite the compressed charge of air/fuel
vapour ( Fig. 2.314 ).
For a spark to jump across an air gap of 1.0 mm under normal atmospheric
conditions (1 bar) a voltage of 4–5 kV is required. For a spark to jump across a
similar gap in an engine cylinder, having a compression ratio of 8:1, approximately
10 kV is required. For higher compression ratios and weaker mixtures, a voltage
up to 20 kV may be necessary. The ignition system has to transform the normal
battery voltage of 12 V to approximately 8–20 kV and, in addition, has to deliver
this high voltage to the right cylinder, at the right time. Some ignition systems will
supply up to 40 kV to the spark plugs.