Investigation of the ignition process using electrical spark ignition on a single-stroke engine (RCEM).

Due to the steady trends towards higher mean pressures and leaner mixtures in the field of large gas engines, reliable ignition of the mixture in the combustion chamber is of great importance in order to keep cyclic combustion fluctuations within an acceptable range. For this, an in-depth understanding of the processes during ignition and in the early phase of combustion is essential.

Therefore, the single-stroke engine (Rapid Compression Expansion Machine, RCEM) available at IVT was used in combination with an electric spark ignition system to investigate in detail the influence of the burning duration of the ignition spark on the early phase of flame nucleation in premixed gas-air mixtures under defined boundary conditions and with excellent optical accessibility. The experimental procedure used for this purpose is explained in more detail with reference to Figure 1.

Figure 1: Test procedure for investigating the ignition process on the single-stroke engine.

For the tests, the combustion chamber was first evacuated in the initial position of the piston. Then the lean gas-air mixture, which had already been mixed in advance, was filled in at the desired pressure. Finally, the piston was pneumatically shot to top dead center and combustion was initiated at a defined ignition timing.

For fundamental analysis of the processes in the combustion chamber, optical images were taken in the area of the spark plug electrode using a schlieren setup and a high-speed camera. A selected result of this investigation is shown in Figure 2 and illustrates that the initial flame core in the spark plug electrode region develops more slowly at a spark burning duration of 100 µs than at 500 µs. However, an important finding is also that there are limits to the acceleration of flame nucleation by increasing the spark burning duration, since there is no change in the combustion process after a certain duration (not shown). RCEM can be used to investigate many other issues in the field of flame nucleation. In particular, the influences of the ignition system settings and the spark plug geometry can be examined in detail.