Enabling HCCI combustion of n-heptane through thermo-chemical recuperation
Bibliographic record
Abstract
Concerns over air quality, environmental regulatory requirements and the need for reducing fuel consumption on conventional internal combustion engines (ICE) have motivated the development of alternative combustion processes for ICE. One alternative, homogeneous charge compression ignition (HCCI), has shown benefits of high efficiency with low NOx emissions, but suffers load range limitations and control issues. An increase in equivalence ratio at constant speed changes the combustion timing relative to top dead center (TDC), and also increases the pressure rise rate. The opposite occurs if the equivalence ratio is reduced, delaying the combustion timing with respect to TDC and reducing the peak pressure. Excessive heat release associated with richer mixtures drives the engine to ringing conditions, which sets the upper limit for HCCI operation. This thesis aims to investigate numerically the HCCI process under dual fuel operation. The secondary fuel stream bears different autoignition characteristics to regulate combustion timing and heat release at specific operational conditions. The secondary fuel stream is produced onboard as a reformed product of the primary fuel. The reforming process, which requires additional steam, takes advantage of the exhaust gases to convey the fuel reforming reactions, process that is called thermo-chemical recuperation (TCR). This thesis contributes to understanding the effects of different system conditions on the integrated HCCI-TCR system operational range and emissions of nitrogen oxides (NOX), and carbon monoxide (CO).;Using n-heptane as the main fuel for HCCI combustion and fuel reforming, two different HCCI models are developed and validated. The single-zone model allows for studying the effect of the secondary fuel on combustion timing. A more complex model, the multi-zone model, allows for studying the effect of secondary fuel on overall engine performance and emissions. Both models operate under engine steady state assumptions (constant speed-load conditions). The combustion models were linked through a cycle simulation code to predict gas exchange processes, in particular the exhaust gas process which defines reforming conditions in the TCR. A model to predict the secondary fuel stream composition on the steam-fuel reformer, under steady state conditions, is developed and validated. Using n-heptane and steam as reactants, the model is able to predict the reformed gas (RG) concentration at the reformer outlet as a function of reforming temperature and relative initial molar fractions of n-heptane and water. The model results are compared against experimental work on steam reforming of n-heptane. RG composition obtained is used to substitute n-heptane at the intake, which
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".