Progress and recent trends in homogeneous charge compression ignition (HCCI) engines

Review of high efficiency and clean reactivity controlled compression ignition (RCCI) combustion in internal combustion engines

Plasma assisted combustion: Dynamics and chemistry

A fuel reactivity controlled compression ignition (RCCI) concept is demonstrated as a promising method to achieve high efficiency – clean combustion. Engine experiments were performed in a heavy-duty test engine over a range of loads. Additionally, RCCI engine experiments were compared to conventional diesel engine experiments. Detailed computational fluid dynamics modelling was then used to explain the experimentally observed trends. Specifically, it was found that RCCI combustion is capable of operating over a wide range of engine loads with near zero levels of NOx and soot, acceptable pressure rise rate and ringing intensity, and very high indicated efficiency. For example, a peak gross indicated efficiency of 56 per cent was observed at 9.3 bar indicated mean effective pressure and 1300 rev/min. The comparison between RCCI and conventional diesel showed a reduction in NOx by three orders of magnitude, a reduction in soot by a factor of six, and an increase in gross indicated efficiency of 16.4 per cen...

https://journals.sagepub.com/doi/pdf/10.1177/1468087411401548

Fuel reactivity controlled compression ignition (RCCI): a pathway to controlled high-efficiency clean combustion

Turbulent premixed combustion: Flamelet structure and its effect on turbulent burning velocities

Demonstrating the Multi Fuel Capability of a Homogeneous Charge Compression Ignition Engine with Variable Compression Ratio

https://www.engr.colostate.edu/~marchese/combustion10/2.pdf

Partially Premixed Combustion (PPC) provides the potential of simultaneous reduction of NOx and soot for diesel engines. This work attempts to characterize the operating range and conditions required for PPC. The characterization is based on the evaluation of emission and in-cylinder measurement data of engine experiments. It is shown that the combination of low compression ratio, high EGR rate and engine operation close to stoichiometric conditions enables simultaneous NOx and soot reduction at loads of 8bar, 12bar, and 15bar IMEP gross. The departure from the conventional NOx-soot trade-off curve has to be paid with a decline in combustion efficiency and a rise in HC and CO emissions. It is shown that the low soot levels of PPC come along with long ignition delay and low combustion temperature. A further result of this work is that higher inlet pressure broadens the operating range of Partially Premixed Combustion.

Characterization of Partially Premixed Combustion

An experimental study of the Homogeneous Charge Compression Ignition (HCCI) combustion process has been conducted by using chemiluminescence imaging. The major intent was to characterize the flame structure and its transient behavior. To achieve this, time resolved images of the naturally emitted light were taken. Emitted light was studied by recording its spectral content and applying different filters to isolate species like OH and CH.Imaging was enabled by a truck-sized engine modified for optical access. An intensified digital camera was used for the imaging. Some imaging was done using a streak-camera, capable of taking eight arbitrarily spaced pictures during a single cycle, thus visualizing the progress of the combustion process. All imaging was done with similar operating conditions and a mixture of n-heptane and iso-octane was used as fuel.Some 20 crank angles before Top Dead Center (TDC), cool flames were found to exist. They appear with a faint structure, evenly distributed throughout the combustion chamber. There was no luminosity recorded between the end of cool flames and the start of the main heat release. Around TDC the main heat release starts. Looking at a macro scale, we find that the charge starts to burn simultaneously at arbitrary points throughout the charge. Since the thermal boundary layer is colder than the bulk of the charge, the local heat release is delayed close to the walls. As a result, the total heat release is slowed down. Ensemble averaged1 images show this wall boundary effect clearly when plotted against CAD. The peak intensity at the main combustion event is one order of magnitude greater than that of the cool flame and the structure is a lot more protruding.Since spontaneous emission imaging is a line-of-sight integration, the flame structure appears a bit smeared. The micro scale structure is very similar from one cycle to another, but there are large variations between cycles on the macro scale. (Less)

A Study of the Homogeneous Charge Compression Ignition Combustion Process by Chemiluminescence Imaging

The HCCI Combustion Process in a Single Cycle - High-Speed Fuel Tracer LIF and Chemiluminescence Imaging

The Hcci Combustion Process in a Single Cycle-High-Speed Fuel Tracer Lif and Chemiluminescence Imaging

Auto-ignition with SI-compression ratio can be achieved by replacing some of the fresh charge by hot residuals. In this work an engine is run with a negative valve overlap (NVO) trapping hot residuals. By increasing the NVO, thus raising the initial charge temperature it is possible to investigate the intermediate zone between SI and HCCI as the amount of residuals is increased. Recent research has shown the potential of using spark assistance to aid gasoline HCCI combustion at some operating conditions, and even extend the operating regime into regions where unsupported HCCI combustion is impossible. In this work the influence of the spark is studied in a single cylinder operated engine with optical access. Combustion is monitored by in-cylinder pressure and simultaneous high speed chemiluminescence imaging. It is seen that even for large NVO and thus high residual fractions it is a growing SI flame that interacts with, and governs the subsequent HCCI combustion. Using the spark timing it is possible to phase the combustion timing even when the major part of the released heat is from HCCI combustion. The flame expansion speed is decreases for higher NVO, but prevails also for high residual fractions. A higher spark advance is found to compensate for the slower flame expansion up to a point. The auto-ignition process is found to be stratified for both spark assisted HCCI as well as for pure HCCI. For pure HCCI the initial front spreading velocity is found to be in the same order of magnitude as for the expansion speed of the SI flame. Calculations to estimate the crank angle of auto-ignition are performed based on cylinder pressure information providing good statistics on how the proportion of SI to HCCI behaves for different operating conditions.

Anders Hultqvist

Papers

Demonstrating the Multi Fuel Capability of a Homogeneous Charge Compression Ignition Engine with Variable Compression Ratio

Characterization of Partially Premixed Combustion

A Study of the Homogeneous Charge Compression Ignition Combustion Process by Chemiluminescence Imaging

The Hcci Combustion Process in a Single Cycle-High-Speed Fuel Tracer Lif and Chemiluminescence Imaging

Investigation of the Early Flame Development in Spark Assisted HCCI Combustion Using High Speed Chemiluminescence Imaging