Cylinder Pressure Based Method for In-Cycle Pilot Misfire Detection
Abstract:
For the reduction of emissions and combustion noise in an internal combustion
diesel engine, multiple injections are normally used. A pilot injection reduces
the ignition delay of the main injection and hence the combustion noise.
However, normal variations of the operating conditions, component tolerances,
and aging may result in the lack of combustion i.e. pilot misfire. The result is
a lower indicated thermal efficiency, higher emissions, and louder combustion
noise. Closed-loop combustion control techniques aim to monitor in real-time
these variations and act accordingly to counteract their effect. To ensure the
in-cycle controllability of the main injection, the misfire diagnosis must be
performed before the start of the main injection. This paper focuses on the
development and evaluation of in-cycle algorithms for the pilot misfire
detection.
Based on in-cylinder pressure measurements, different approaches to the design of
the detectors are compared. For non-adaptive methods, a constant threshold,
direct misfire probability, and posterior misfire probability detectors are
investigated. For adaptive methods, an adaptive threshold update is suggested,
an adaptation of the predictive stochastic models and a sensor fusion of them is
proposed to increase the detection performance.
A Scania D13 engine is used to perform the experiments under different operating
conditions. The effectiveness of the algorithms is tested for different engine
speeds, rail pressures, injection durations, starts of injection, EGR levels,
and fuels. The results show that the observability of in-cycle pilot misfire
depends on the operating conditions, and its detection can be performed
successfully before the start of the main injection. With a maximum in-cycle
pilot misfire observability of 98.5%, a maximum successful detection ratio of
about 96% can be reached with the proposed in-cycle pilot misfire detectors. The
algorithms are therefore suitable for in-cycle closed-loop combustion control
feedback. By including cycle-to-cycle adaptation, the detection performance and
robustness are improved significantly. The limitations are directly related to
the signal-to-noise ratio of each operating condition.