Compression Ratio Influence on Maximum Load of a Natural Gas Fueled HCCI Engine

Abstract

This paper discusses the compression ratio influence on maximum load of a Natural Gas HCCI engine. A modified Volvo TD100 truck engine is controlled in a closed-loop fashion by enriching the Natural Gas mixture with Hydrogen. The first section of the paper illustrates and discusses the potential of using hydrogen enrichment of natural gas to control combustion timing. Cylinder pressure is used as the feedback and the 50 percent burn angle is the controlled parameter. Fullcycle simulation is compared to some of the experimental data and then used to enhance some of the experimental observations dealing with ignition timing, thermal boundary conditions, emissions and how they affect engine stability and performance. High load issues common to HCCI are discussed in light of the inherent performance and emissions tradeoff and the disappearance of feasible operating space at high engine loads. The problems of tighter limits for combustion timing, unstable operational points and physical constraints at high loads are discussed and illustrated by experimental results. Finally, the influence on operational limits, i.e. emissions peak pressure rise and peak cylinder pressure, from compression ratio at high load are discussed.

Combustion Chamber Wall Temperature Measurement and Modeling During Transient HCCI Operation

“…The lack of feedback combustion control makes it impossible to break the instability. Combustion instability is a known phenomenon in HCCI engines, discussed by Olsson et al [14]. Olsson et al find that HCCI combustion phasing during some circumstances drifts.…”

“…The compression ratio can be increased, the inlet air can be pre heated, the HCCI combustion can be triggered by the use of retained hot residual gas and the octane number of the fuel can be altered [2]- [8]. Since the HCCI combustion process is very sensitive to numerous parameters, feedback combustion control is needed to operate an HCCI engine in parts of its operation range as shown by Olsson et al [14]. Such combustion control can be performed in numerous ways using different actuators [10]- [13].…”

“…The HCCI combustion is as shown by Olsson et al [14] very sensitive to the temperature history of the engine; this paper focuses on the behavior of the wall temperature when a sudden change of engine load (a load transient) occurs. Investigations of the wall temperature behaviour of an HCCI engine have previously been performed by the use of thermocouples by Chang et al [15].…”

Hydrogen Addition For Improved Lean Burn Capability of Slow and Fast Burning Natural Gas Combustion Chambers

“…The properties of the engine are summarized in Table 2. The combustion control system is a modified version of the system used previously in [10]. The cylinder pressure trace and the inlet conditions are sampled and some key parameters characterizing the operating condition are calculated in real time.…”

Boosting for High Load HCCI

“…To optimize efficiency and minimize NO X emissions compression ratio should be selected as high as possible, so that at peak load the control variables almost saturate [29]. If intake temperature is used for control, the lowest intake temperature that can always be guaranteed must be low enough to prevent too early combustion at full load.High backpressure, and thereby high fraction of hot residual gases, at full load will significantly increase the charge temperature and thereby limit the compression ratio.…”