Racing – Combustion Measurement Technology

“Make the right decisions and make them more quickly.” The purpose of doing measurements is in exploiting measurement results to support such decision making.

In racing applications, combustion measurement techniques are required to give guidance in exploiting engine features for highest power output, engine reliability and lowest possible system inertia to minimize transient engine response.

Each class of racing cars has its specific speed and load range, and each class has its very special requirements:

Gas exchange, fuel injection and mixture formation, combustion phasing and duration as well as thermal loading of engine components are the defining topics for combustion measurement and variants testing techniques.

Mixture Formation

Evaluation of fuel spray injection is accomplished with optical imaging techniques. This supports exploiting of spray and airflow interactions and it provides best understanding of the risks for fuel wall film formation.

Fuel spray and intake flow interaction in PFI engines is directly seen with methods utilizing intake port endoscopes. Fuel wall wetting and wall film formation is immediately recognized and fuel injection parameters, or best suited injectors, for reducing such fuel storage effects are easily identified. This especially supports precise fuel supply at engine acceleration.

The success of transferring the injected fuel into homogeneous mixture and furthermore its efficient combustion in a turbulent premixed flame is checked with data derived from pressure and flame radiation measurements.

Insufficient mixture quality with heterogeneous and fluctuating vapor and liquid fuel composition, and thus a reduction of combustion stability and torque becomes evident in flame radiation pattern signals. The method of flame pattern evaluation is based on the use of flame radiation signals accessed with optical fibers. Such fiber sensors are implanted in spark plugs or in pressure sensor adapters. The time or more precisely the degree crank angle sequence and the broadband flame signal amplitude allow every cylinder and cycle to be evaluated for mixture formation quality. Perfect premixed combustion is well recognized against combustion with liquid fuel storage effects. Multichannel sensors even provide identification of areas with heterogeneous combustion.

The method applies flame signal recording on a degree crank angle basis. Thus it is capable of operating up to highest engine speed with full cycle and crank angle resolution. This especially supports recording of transient operation. Engine acceleration tests thus are evaluated for their torque response on basis of cylinder pressure signals, for their mixture formation quality, the flame signal analysis method is applied.

Knock Limit Optimization

In the low to mid racing speed range power density is limited by knock as a consequence of selected compression ratio, fuel chemistry and components temperature. Improving such knock limits requires the flame front to burn off potential endgas knock centers before they have a chance to self – ignite.

Thus, optimizing the knock limit requires acceleration of local flame propagation to effectively burn off endgas and it needs enhanced cooling of potential hot spot ignition locations. Which one of such measures is most adequate is recognized from knock center distribution analysis. Knock center measurements are supported with flame kernel propagation measurements and with an analysis of speed and temperature effects on knock behaviour.

Glow Ignition

In engines with very high thermal load, hot surface areas can act as an uncontrollable ignition source of irregular combustion. Recognizing such ignition mechanisms and identifying the hot spot locations are the first tasks in effectively avoiding these riskful irregular combustion events. Ignition locations are identified by means of multichannel fiberoptic sensors. Measurement and recording of such irregular stochastic events is accomplished with the modules and procedures of an engine combustion measurement system.

Find and Use the Best Mix of Inhouse Experience and AVL Expert Services

No matter how useful above techniques are in supporting specific combustion development tasks, in cases with most urgent need for events analysis, an engine development group must first of all find suitable sensors and instrumentation, and must familiarize with the know how to perform diagnostics and results evaluation.

This is precisely the moment to address the AVL “combustion measurement services” group. Their experts have gained their know how and skills in numerous field applications at customers’ and AVL’s in-house test beds. In close cooperation with the client’s engineers they take care for the most effective application of measurement and analysis techniques. As soon as the first group of results becomes available, customer engineers get their own hands-on experience in applying the best mix of AVL services support and inhouse measurement techniques.

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