Homogeneous Charge Compression Ignition Research Articles

Comparison of diesel engine with other engines and NOx scandal

This essay will focus on the comparison of the Homogenous Charged Compression Ignition engine and the Diesel engine. Diesel engine is one of the most widely used engines in the world. It uses fossil fuel such as the gasoline to get power. What is more, it does not need a spark to ignite the fuel. It uses compression method to burn the fuel. However, there is also some problems for this kind of engine, such as the greenhouse effect and the heat loss for this kind of engine. Compared to the Diesel engine, the Homogenous Charged Compression Ignition engine can mix the fuel into a correct ratio before burning. This can improve the efficiency of burning process. It can also improve the energy it released to get more power. There are several solutions to the problem. For example, to reduce the bad effect caused by the fossil fuel, people started to develop the hydrogen fuel. There are also some limitations of the hydrogen, such as expensive cost for producing the hydrogen and the hard storage of hydrogen. Use hydrogen to replace the fuel will face some problems. As a result, improving the efficiency of burning fossil fuel will also be a good choice. The essay also focuses on the scandal of diesel engines, mainly talks about the scandal of the diesel-engine transportation. Diesel engines are the most widely used engine in the world, they will release wastes, pollution and some toxic gases when they are working. Have these scandals been fixed?

Frictional Losses of Ring Pack in SI and HCCI Engine

The vast majority of research dedicated to enhancing the homogenous charge compression ignition (HCCI) low-temperature combustion system is focused on improving controllability, efficiency and emissions. This article aims to assess the impact of HCCI combustion on the operation of the piston ring system. Utilizing the measured pressures in the combustion chamber of a single-cylinder research engine operating in spark ignition (SI) and HCCI modes at various loads, simulations were carried out using an advanced ring pack model. This model integrates the gas flow, ring dynamics and ring mixed lubrication models. Simulations revealed that differences in the pressure above the piston between the HCCI and SI combustion significantly influence ring pack performance. The predicted energy losses due to the friction of piston rings against the cylinder liner are up to 5% higher in the HCCI engine than in the SI engine. This identified drawback diminishes the advantages of the HCCI engine resulting from higher thermal efficiency, and efforts should be made to minimize this negative impact.

Exploring the Impact of Al2O3 Additives in Gasoline on HCCI-DI Engine Performance: An Experimental, Neural Network, and Regression Analysis Approach.

This study delves into the influence of incorporating alumina (Al2O3) nanoparticles with waste cooking oil (WCO) biofuels in a gasoline engine that employs premixed fuel. During the suction phase, gasoline blends with atmospheric air homogeneously at the location of the inlet manifold. The biodiesel, enhanced with Al2O3 nanoparticles and derived from WCO, is subsequently directly infused into the combustion chamber at 23° before the top dead center. The results highlight that when gasoline operates in the homogeneous charge compression ignition with direct injection (HCCI-DI) mode, there is a notable enhancement in thermal efficiency by 4.23% in comparison to standard diesel combustion. Incorporating the Al2O3 nanoparticles with the WCO biodiesel contributes to an extra rise of 6.76% in thermal efficiency. Additionally, HCCI-DI combustion paves the way for a reduction in nitrogen oxides and smoke emissions, whereas biodiesel laced with Al2O3 nanoparticles notably reduces hydrocarbon and carbon monoxide discharges. Predictive tools such as artificial neural networks and regression modeling were employed to forecast engine performance variables.

A Numerical Investigation on Laminar Flame Speed of Syngas in Air with Ozone Addition

In the context of energy and propulsion systems, in recent years engineering research has increased its efforts to develop more efficient technologies with a lower environmental impact. Specifically, new combustion systems have been investigated, such as ultra-lean combustion and Homogeneous Charge Compression Ignition (HCCI) combustion, and sustainable fuels have been employed. With respect to the latter option, syngas and hydrogen have emerged as attractive choices. However, the low specific energy of syngas and the presence of diluents can cause flame failure and instability. On the other hand, it is well known that ozone-assisted combustion enhances the Laminar Flame Speed (LFS), reduces the ignition delay time, and improves the flame stabilization of fuels such as methane, n-heptane and iso-octane, since it affects the chemistry in the Low Temperature Combustion (LTC) regime. In this context, the aim of the present work is to evaluate the effect of ozone on the LFS of syngas/ozone/air mixtures. Specifically, 1-D simulations have been carried out to compute the LFS of CO/H2 and CO/H2/N2 syngas mixtures. The model has been validated against experimental data available in the scientific literature by considering four different reaction mechanisms. Then, the model has been used to perform a parametric analysis by considering different conditions in terms of syngas composition (three different CO/H2 ratios) and equivalence ratio (from 0.5 to 5). The results show that the addition of 2500 ppm of ozone in air results in an increase in LFS for all equivalence ratios examined. The four different mechanisms give comparable results in terms of LFS and LFS increase for CO/H2 syngas, and are also able to predict ozone effect on LFS enhancement for CO/H2/N2 mixtures. Finally, the results show that the influence of ozone, in terms of LFS percentage increase, is greater for CO/H2 ultra lean mixtures with a lower CO/H2 ratio.

The study on the conversion of single cylinder engine into homogeneous charge compression ignition (HCCI) engine

The study on the conversion of single cylinder engine into homogeneous charge compression ignition (HCCI) engine

Experimental study on combustion, performance, and emission characteristics of a homogeneous charge compression ignition engine fuelled with multiple biofuel-gasoline blends

For sustainable future mobility and power generation applications, there is a compelling need to develop flex-fuel engines that operate with multiple regional or season-specific biofuels. The present investigation focussed on mitigating agricultural diesel engines’ pollutant emission and performance problems. A systematic experimental study is carried out in a modified agricultural diesel engine to compare and evaluate the engine characteristics of the biofuel-gasoline blends fuelled Homogeneous Charge Compression Ignition (HCCI) mode. Seven different oxygenated biofuels: acetone, ethanol, methanol, isopropanol, isobutanol, ethyl acetate, and diisopropyl ether blended in gasoline, were investigated. 2-Ethylhexyl nitrate was used to improve the reactivity of fuel blends to the extent that lower engine loads could be reached. All the investigated biofuel-gasoline blends could produce permissible emission levels by suitably tuning the fuel proportions. The total nitrogen oxides and smoke emissions were below 2.8 and 0.0007 g/kWh, respectively, for all the investigated biofuel-gasoline blends at all the HCCI engine load conditions. The highest indicated thermal efficiency of 42% was attained using 60% ethanol/34% gasoline/6% 2-EHN blend in the HCCI engine at 4.63 bar BMEP (86% rated load), a notable 25% improvement compared to the conventional diesel engine. A detailed investigation was done to elucidate the HCCI engine performance (indicated thermal efficiency) trend variations with biofuel type and engine load. The Response Surface Method was adopted to correlate the maximum and the minimum engine load with the fuel composition and properties. The Desirability Approach provided the optimum fuel composition and properties to maximize the engine load range. The optimum solution achieved the engine load range of 20%–89% rated load. Overall, a compact, efficient, and clean HCCI combustion-based engine technology was developed that could be operated using multiple biofuels over an expanded load range.

A co-kurtosis PCA based dimensionality reduction with nonlinear reconstruction using neural networks

For turbulent reacting flow systems, identification of low-dimensional representations of the thermo-chemical state space is vitally important, primarily to significantly reduce the computational cost of device-scale simulations. Principal component analysis (PCA), and its variants, are a widely employed class of methods. Recently, an alternative technique that focuses on higher-order statistical interactions, co-kurtosis PCA (CoK-PCA), has been shown to effectively provide a low-dimensional representation by capturing the stiff chemical dynamics associated with spatiotemporally localized reaction zones. While its effectiveness has only been demonstrated based on a priori analyses with linear reconstruction, in this work, we employ nonlinear techniques to reconstruct the full thermo-chemical state and evaluate the efficacy of CoK-PCA compared to PCA. Specifically, we combine a CoK-PCA-/PCA-based dimensionality reduction (encoding) with an artificial neural network (ANN) based reconstruction (decoding) and examine, a priori, the reconstruction errors of the thermo-chemical state. In addition, we evaluate the errors in species production rates and heat release rates, which are nonlinear functions of the reconstructed state, as a measure of the overall accuracy of the dimensionality reduction technique. We employ four datasets to assess CoK-PCA/PCA coupled with ANN-based reconstruction: zero-dimensional (homogeneous) reactor for autoignition of an ethylene/air mixture that has conventional single-stage ignition kinetics, a dimethyl ether (DME)/air mixture which has two-stage (low and high temperature) ignition kinetics, a one-dimensional freely propagating premixed ethylene/air laminar flame, and a two-dimensional dataset representing turbulent autoignition of ethanol in a homogeneous charge compression ignition (HCCI) engine. Results from the analyses demonstrate the robustness of the CoK-PCA based low-dimensional manifold with ANN reconstruction in accurately capturing the data, specifically from the reaction zones.

Frontier development and prospect trend of HCCI engine

Nowadays, with the rapid development of information technology, the level of science and technology is constantly improving. All fields are developing rapidly. In recent years, the development of the automotive engine industry has been particularly rapid. To cope with increasingly strict environmental requirements and the impact of electric motors on the market, a new engine model is gradually being valued. Homogeneous Charge Compression Ignition (HCCI) internal combustion engine is a new type of engine. It has the technical advantages of traditional diesel and gasoline engines. This combustion mode greatly improves the emission of pollutants and the engine’s overall efficiency. However, there are still certain challenges to this technology at present. But with the continuous improvement and optimization of related technologies. HCCI engines are bound to have broad development prospects. This article elaborates on the current status and development trends of HCCI engines from four perspectives: basic principles, combustion characteristics, emission characteristics, and the latest developments.

Effect on minor addition of aromatic (benzyl alcohol) and diethyl ether in Calophyllum inophyllum blended diesel fuel in a CI engine operates by hydrogen energy as a secondary fuel

Strict regulations on vehicle emissions are in place to lessen pollution and environmental damage. The depletion of fossil fuels also threatens energy security. Renewable, cleaner-burning and sustainable fuels could aid the researcher in solving these problems. Because of their limited supply, renewable fuels cannot resolve the issue independently. Therefore, much research is being done on enhanced combustion technologies, such as dual-fuel engines, homogenous charge compression ignition, and low-temperature combustion. The Calophyllum inophyllum oil (P20) mixed with diesel, diethyl ether, and aromatic alcohol (benzyl alcohol) was tested in this study using a dual-fuel engine. Hydrogen gas is added to the air intake manifold as a second energy source. Aromatic alcohol is an organic fuel that can be produced naturally by hydrolysis of lignin. The OH hydroxyl group is attached to the aromatic ring and promotes free radical propagation. Minor addition of oxygenates affects the performance, combustion, and emission of engines operating on various loads. Maximum brake thermal efficiency and lower brake-specific fuel consumption were observed with 20 % aromatic alcohol, 32.45 %, and 0.2 kg/kW-hr, respectively. Brake thermal efficiency improved to 6.54 % compared to neat diesel. Reduction in brake-specific fuel consumption by 28 % compared to diesel fuel. Compared to other blends, aromatic alcohol additions are linked to reduced smoke, HC, and CO emissions. However, using aromatic alcohol results in slightly increased nitrogen oxide emissions compared to diesel. Blends of biofuel and benzyl alcohol have shown favorable effects in terms of enhanced combustion, reduced emissions, and increased efficiency.

LSTM for Modeling of Cylinder Pressure in HCCI Engines at Different Intake Temperatures via Time-Series Prediction

Modeling engines using physics-based approaches is a traditional and widely-accepted method for predicting in-cylinder pressure and the start of combustion (SOC). However, developing such intricate models typically demands significant effort, time, and knowledge about the underlying physical processes. In contrast, machine learning techniques have demonstrated their potential for building models that are not only rapidly developed but also efficient. In this study, we employ a machine learning approach to predict the cylinder pressure of a homogeneous charge compression ignition (HCCI) engine. We utilize a long short-term memory (LSTM) based machine learning model and compare its performance against a fully connected neural network model, which has been employed in previous research. The LSTM model’s results are evaluated against experimental data, yielding a mean absolute error of 0.37 and a mean squared error of 0.20. The cylinder pressure prediction is presented as a time series, expanding upon prior work that focused on predicting pressure at discrete points in time. Our findings indicate that the LSTM method can accurately predict the cylinder pressure of HCCI engines up to 256 time steps ahead.

Investigation of conversion of a diesel engine to homogeneous charge compression ignition engine using n-heptane: A zero-dimensional modeling

Numerical methods are commonly used for analyzing combustion characteristics. Besides, they provide an opportunity to predict emissions of an engine. In this paper, the conversion of a single-cylinder diesel engine to HCCI combustion model is investigated with AVL Boost v2021R2. The model was used to simulate the power, emission, bsfc value. In-cylinder pressure results also are obtained from the model. Verification of the model is conducted with experimental data from the literature. The differentiation between the numerical and experimental results remained below 8.9% for the power, below 6.62% for bsfc. In addition to this, the model gave maximum pressure values with an accuracy of ± 1%, and maximum HRR values with an accuracy of ± 2%. Maximum HRR values and in-cylinder pressure curves for 1200-2400 rpm were obtained with acceptable accuracy. Besides, the operating range of an HCCI engine fueled with n-heptane was investigated using a zero-dimensional single-zone model with reduced fuel chemistry. The compression ratio and inlet air temperature effect on HCCI combustion were analyzed. The increasing the air inlet temperature to 40oC from 20oC, increases the lowest air-fuel ratio about 6.6% which the engine can operate without entering the knock zone, at 17.5 CR at 1200rpm.

Development and assessment of a novel natural gas fuelled HCCI engine based combined power, heating, and refrigeration system

Internal combustion engines waste a significant amount of energy from the fuel they consume, mostly through the atmospheric release of engine exhaust gases. This phenomenon is well acknowledged as a significant contributor to engine inefficiencies and the production of harmful pollutant emissions. In order to tackle this issue, a bottoming cycle that combines a supercritical CO2 (S–CO2) power cycle with an ejector refrigeration cycle (ERC) is implemented. The goal is to generate power, heating, and cooling utilizing waste heat from a natural gas-powered homogeneous charge compression ignition (HCCI) engine. The study found that the HCCI engine, when not utilizing a bottoming cycle, demonstrated thermal and exergy efficiencies of 48.30% and 40.83%, respectively. However, the incorporation of S–CO2 and ERC cycles resulted in significantly higher system efficiencies of 64.90% and 48.84%, respectively. Furthermore, the proposed system has thermal efficiencies of 53.86% for electrical output, 7.801% for heating output, and 3.239% for cooling output. In addition, the HCCI engine accounts for the most exergy destruction in the system, accounting for 92.83 kW (25.72%), with losses due to in-cylinder heat transfer and system exhaust accounting for 20.63 kW (5.72%) and 12.52 kW (3.47%), respectively.

A comprehensive review into the effects of different parameters on the hydrogen‐added HCCI diesel engine

AbstractThe current study presents research investigations and developments related to the homogeneous charge compression ignition (HCCI) engine. Research investigations and recent advances, including the role of various operating conditions on HCCI engine combustion phenomena, emissions, and performance, are discussed. There is growing research interest in investigating HCCI engines with diesel fuel to study combustion, emissions, and performance characteristics due to their association with low NOx emissions. In the published literature, research investigations are also conducted with different fuels ranging from biomass to diesel to gasoline in the HCCI engine showing its capability for utilizing various fuels in coming years. The challenges associated with HCCI combustion are reviewed, and the details of excessive carbon monoxide and unburnt hydrocarbon emissions are discussed. The major parameters affecting the hydrogen addition in HCCI diesel engines are also discussed. Overall, adding hydrogen to a diesel‐fueled HCCI engine improves combustion phasing and can potentially increase thermal efficiency while lowering emissions. In addition, the strength, weaknesses, opportunities, and threat analysis is provided and discussed thoroughly.

Effects of water direct injection on a combustion phase and performance of six-stroke gasoline homogeneous charge compression ignition engine

An experimental study was conducted to examine how direct water injection (WI) can optimize the combustion phases of a six-stroke gasoline homogenous charge compression ignition (HCCI) engine. With six-stroke HCCI combustion, the limitations of four-stroke HCCI combustion under high loads and the stability of combustion under low loads can be resolved by adding additional compression and expansion stroke. Previous six-stroke HCCI combustion research suggested that the time loss could be reduced by delaying the combustion phase to the top dead center (TDC) with additional cooling. Thus, in this study, the effects of WI on the overall pressure curve, as well as the first and second combustion phases, were studied from a thermal and chemical kinetics perspective. The performance, thermal efficiency, and pressure rise rate were also examined. It was found that WI retarded the first and second combustion. The first and second combustion phases were located after and before TDC, respectively, resulting in a decrease in the first gross mean effective pressure (GMEP) (180–540 CA) and an increase in the second GMEP (540–900 CA). Because the increase of second GMEP was dominant, the indicated thermal efficiency also monotonically increased (2.7–3.5%p). In addition, the maximum pressure rise rate decreased by 23.1% to 65.2%. Thus, the WI can be used to control the combustion characteristics of six-stroke gasoline HCCI engine.

Numerical investigation on selecting appropriate piston bowl geometry and compression ratio for gasoline-fuelled homogeneous charge compression ignited light-duty diesel engine

The gasoline-fuelled homogeneous charge compression ignition (HCCI) combustion is a promising approach to mitigate the significant limitations of the traditional compression-ignition combustion for light-duty engine applications. In the present work, the required autoignition quality of gasoline was achieved by blending 2-ethylhexyl nitrate (EHN) with gasoline to ensure combustion stability at the achieved engine loads. A reduced chemical reaction mechanism consisting of 185 species and 219 reactions was developed in the present study for EHN-gasoline-fuelled-HCCI combustion. The mechanism was validated by conducting multi-dimensional computational fluid dynamics (CFD) simulations of HCCI combustion in a modified light-duty diesel engine. A detailed numerical study was done using the validated CFD model to select the suitable piston bowl geometry and geometric compression ratio for better engine performance and lower regulated emissions. Eleven different piston bowl geometries were explored, which also included piston bowl designs popular in traditional compression-ignition (toroid) and spark-ignition (flat) engines. The results indicated that the flat-shaped piston bowl exhibited a 17% improvement in the gross indicated thermal efficiency and a 16% and 40% reduction in UHC and CO emissions while maintaining very low NOx and smoke levels compared to the baseline hemisphere-shaped piston bowl. The engine performance remained the same for the flat-shaped piston bowl geometry even for a 17% increased compression ratio with the added benefit that the reduced EHN concentration (by 48 vol.%) was needed to achieve the same combustion phasing. Thus, the present numerical work proposes a promising approach to improve the overall performance of gasoline-fuelled HCCI combustion by piston bowl design and compression ratio optimization.

An analytical approach to converting vibration signal to combustion characteristics of homogeneous charge compression ignition engines

Homogeneous charge compression ignition (HCCI) is a promising low-temperature combustion technique for low-emission internal combustion engines. Unlike conventional engines, HCCI lacks a direct ignition control mechanism, necessitating closed-loop combustion control. This study proposes a phenomenological-based, cost-effective, and non-intrusive approach using vibration data analysis to determine essential combustion parameters. Experiments were conducted on a single-cylinder research engine with an accelerometer attached to the engine head. The engine operation envelope covered the whole engine’s operating area in naturally aspirated HCCI mode. Wavelet analysis revealed that combustion-related frequencies centered around 500 Hz, independent of operating conditions. The correlation-seeking analysis included peak acceleration amplitude and its crank angle with peak heat release rate (HRR) data. The peak HRR location was accurately identified within one degree when vibration amplitude exceeded the 100 m/s2 threshold. This encompassed 98.5% of the analyzed combustion cycles. The peak HRR prediction accuracy had a maximum error below 21% and was suitable to monitor reaction rates, especially in incomplete combustion and high ringing cycles.

Effects of temperature and composition inhomogeneity on the ignition characteristics of NH3/H2 co-firing fuels under HCCI operating conditions

The application of ammonia (NH3) in combustion devices, such as internal combustion engines (ICEs), is expected to largely reduce the greenhouse gas (CO2) emission. NH3/H2 cofiring fuels in homogeneous charge compression ignition (HCCI) engines may provide a potential way to deal with zero carbon requirements. However, in HCCI engines, the ignition process needs to be moderated since the ignition is only controlled by the chemical kinetics of the fuel. Therefore, this study investigates the effects of temperature and composition stratification strategies on the auto-ignition characteristics of NH3/H2/air mixtures under HCCI engine operating conditions with direct numerical simulation (DNS). 12 cases with different stratification strategies have been set under turbulent conditions. The chemical kinetics of NH3/H2/air was verified with the laminar flame speeds and ignition delay times. Results show that the temperature stratification can reduce the peak value of heat release rate (HRR), advance the ignition time and extend the combustion duration. In this case, the chemical reaction front is dominated by the deflagration or flame propagation mode. However, in contrast, composition stratification shows very limited effect on the overall combustion process, which is similar to homogeneous ignition and denoted as the spontaneous ignition mode. When increasing the hydrogen content in the fuel, the ignition time is obviously advanced and the peak of HRR is slightly increased. Higher NO emission is also observed which is mainly due to the increase of O, H, and OH intermediates to enhance the fuel NO production. Temperature stratification degree can improve the ignition process under both negatively correlated or unrelated T-Φ fields. However, the improvement is more evident for unrelated T-Φ condition when increasing the stratification degree.

Effects of hydrogen and EGR on energy efficiency improvement with ultra low emissions in a common rail direct injection compression ignition engine fueled with dimethyl ether (DME) under HCCI mode

This study deals with enhancing the energy efficiency with ultra-low emissions and extending the operating range (maximum load limit) of dimethyl ether (DME) fueled homogeneous charge compression ignition (HCCI) engine using hydrogen and exhaust gas recirculation (EGR). In the neat DME mode, the possible maximum load limit with controlled auto-ignition (CAI) was found as 24% (BMEP of 1.67 bar). Beyond 24% load, the knocking was observed with an advanced combustion phase, and shortened combustion duration resulted in uncontrolled auto-ignition (UAI) combustion. The addition of EGR extended the maximum load limit to 52% (BMEP of 3.62 bar) (60% EGR). Near-zero levels of NOx, zero smoke, and marginal CO and HC emissions reduction were observed with the optimized EGR rate (35%). The hydrogen fuel addition along with DME at an optimized EGR rate resulted in combustion phase retardation with the elimination of the low-temperature reaction (LTR) region. The energy efficiency (EE) and indicated thermal efficiency (ITE) increased along with zero smoke emission, ultra-low NOx, CO, and HC, and lower CO2 emissions till 12% of hydrogen energy share (HES). Thus, the combined strategy of EGR and hydrogen could effectively extend the operating range with ultra-low emissions levels.

Technical design of an innovative biomass/gasification-driven power plant with heat recovery hybrid system: CO2 emission comparison between the designed plant and fossil fuel-powered plants

This study aims to introduce, conceptualize, and design a novel biomass/gasification-driven hybrid energy configuration. The proposed hybrid configuration has four subsystems: reformer solid oxide fuel cell (RSOFC), biomass/gasification, homogeneous charge compression ignition engine (HCCIE) plus waste heat recovery system (WHRS). RSOFC and HCCIE systems are embedded to generate electric energy. The syngas required for these two subsystems is captured from the biomass/gasification subsystem. In addition to generating electrical energy, fuel cell is responsible for providing combustible fuel to the HCCIE subsystem. The embedded engine in the system can improve the proposed configuration efficiency by increasing the rate of electrical energy production. In addition, the dissipated heat of fuel cell and engine subsystems is recovered by WHRS. The proposed energy configuration is evaluated and discussed from energetically, exergetically and exergoeconomic and environmental aspects to obtain a comprehensive feasibility study of the plant. The offered hybrid design has new component's structure and relationships that have not been reported in the publications. The analysis indicated that the proposed hybrid configuration is capable of generating approximately 1100 kW and 366.3 W of electric and thermal power, respectively, with the overall energetic and exergetic efficiencies of 69.4% and 52.1%. Exergoeconomic analysis results revealed that the specific fuel cost of the total proposed configuration was approximately 1.96 USD per GJ. In addition, compared to a coal and petroleum oil-based power generation plants, the proposed hybrid configuration can have approximately 2.75-fold and 97.7% lower CO2 emissions, sequentially. Besides, the proposed system can rival other similar biomass-driven designs.

The effect of 1-octanol blending on the multi-stage autoignition of conventional diesel and HVO fuels

Alternative fuels can reduce the carbon intensity of diesel engine use, and a detailed understanding of the combustion process for these fuels can minimize resulting fuel consumption and emissions. 1-Octanol has been considered as an alternative diesel fuel, but little work evaluating its combustion process in detail exists. In this work, ignition of 1-octanol, both pure and in blends with conventional and renewable diesel base fuels, is analyzed in a constant volume combustion chamber and a modified Cooperative Fuels Research Octane Rating engine operating in homogeneous charge compression ignition combustion mode. 1-Octanol blending reduced the derived cetane number of either base fuel, but modest increases in chamber temperature at injection could compensate for even dramatic reductions in derived cetane number. It was further found that greater amounts of low-temperature heat release were required to reach main ignition as the 1-octanol blending volume fraction was increased in the constant volume combustion chamber. This finding is attributed to the changing local equivalence ratio, as the reacting spray diffuses further into the chamber and approaches the (lean) global equivalence ratio as the ignition delay grows. Finally, it was found that, despite lowering the derived cetane number, 1-octanol blending enhanced the reactivity of the conventional diesel fuel observed in the variable compression ratio engine. This finding is attributed to the higher rates of hydrogen abstraction from the weaker average C–H bonds in 1-octanol, as hydrogen abstraction governs intermediate temperature heat release. These findings clarify the effect of 1-octanol on physical processes and the various chemical regimes of heat release in compression ignition. The dependence of the effects of 1-octanol blending on the base fuel are emphasized, as these can inform the deployment of 1-octanol as a diesel blendstock. Application of these results can support the optimization of conventional combustion strategies for use with 1-octanol, as well as the development of 1-octanol-fueled low-temperature combustion strategies with the associated promise of very low criteria pollutant emissions.