Some of the advantages of fuel injection are: 

• No carburetor icing. 

Better fuel flow. 

• Faster throttle response. 

Precise control of mixture. 

• Better fuel distribution. 

Easier cold weather starts. 

Disadvantages include: 

• Difficulty in starting a hot engine. 

Vapor locks during ground operations on hot days. 

• Problems associated with restarting an engine that quits because of fuel starvation. 

## Ignition System 

The ignition system provides the spark that ignites the fuel-air mixture in the cylinders. Components include a magneto generator, an electronic control box that replaces mechanical points, spark plugs, high-voltage leads and the ignition switch(es). Individual manu- facturer designs will vary and pilots must be familiar with the aircraft operating procedures for the PPC be- ing flown. 

A magneto uses a permanent magnet to generate an electrical current independent of the aircraft’s elec- trical system which might include a battery. The air- craft electrical system can fail—the battery can go dead—however, this has no effect on the ignition sys- tem which uses a separate generator in the magneto. The electricity from the separate ignition coil on the magneto generator goes into the ignition control box where the correct voltage is produced and timed to fire the spark plugs at the proper time. The magneto also sends a signal to the electric control box to pro- vide the timing signal to fire the spark plugs. 

Most modern PPCs use an electronic timing system instead of the mechanical points inside the old magne- tos which also housed the points. Capacitor discharge ignition (CDI) systems are a common example of an electronic ignition system. Electronic ignition sys- tems operate without any moving parts to increase reliability and efficiency. A CDI system begins to fire when the starter is engaged and the crankshaft begins to turn. It continues to operate whenever the crank- shaft is rotating. 

Most powered parachutes incorporate a dual ignition system with two individual coil systems in the mag- neto, two individual electronic ignition timing sys- tems (electric box), two separate sets of wires, and 

two spark plugs per cylinder. Dual ignition systems increase overall reliability of the engine. Each igni- tion system operates independently to fire one of the two spark plugs. If one ignition system fails, the other is unaffected. The engine will continue to operate nor- mally, although you can expect a slight decrease in engine power. 

The operation of the ignition system is controlled in the cockpit by the ignition switch(es). Since there are two individual ignition systems, there are normally two separate ignition toggle switches. 

You can identify a malfunctioning ignition system during the pretakeoff check by observing the decrease in RPM that occurs when you first turn off one igni - tion switch, turn it back on, and then turn off the other. A noticeable decrease in engine RPM is normal dur- ing this check. If the engine stops running when you switch to one ignition system or if the RPM drop ex- ceeds the allowable limit, do not fly the powered para - chute until the problem is corrected. The cause could be fouled plugs, broken or shorted wires between the magneto and the plugs, or improperly timed firing of the plugs because of the control box. 

It should be noted that “no drop” in RPM is not nor- mal, and in that instance, the powered parachute should not be flown. Following engine shutdown, keep the ignition switches in the OFF position. Even with the battery and master switches OFF, the engine can fire and turn over if you leave an ignition switch ON and the propeller is moved because the ignition system requires no outside source of electrical power. The potential for serious injury in this situation is ob- vious. 

## Combustion 

During normal combustion, the fuel-air mixture burns in a very controlled and predictable manner. Although the process occurs in a fraction of a second, the mix- ture actually begins to burn at the point where it is ignited by the spark plugs, then burns away from the plugs until it is consumed completely. This type of combustion causes a smooth buildup of temperature and pressure and ensures that the expanding gases de- liver the maximum force to the piston at exactly the right time in the power stroke. 

Detonation is an uncontrolled, explosive ignition of the fuel-air mixture within the cylinder’s combustion chamber. It causes excessive temperatures and pres- sures which, if not corrected, can quickly lead to fail- ure of the piston, cylinder, or valves. In less severe 

