Homogeneous Charge Compression Ignition Mode Research Articles

Computational analysis of ammonia-hydrogen blends in homogeneous charge compression ignition engine operation

Ammonia (NH3) is considered a promising alternative fuel due to its renewable and carbon-free nature. The addition of hydrogen (H2) significantly improves its flammability, making it suitable for use in internal combustion engines. The homogeneous charge compression ignition (HCCI) technique offers a practical solution for high-efficiency NH3-H2 operation, but it is not extensively discussed in existing literature. To enhance the understanding of NH3-H2 HCCI engines, this study employs a zero-dimensional model validated against experimental results to investigate engine efficiency and nitrogen oxides (NOx) emissions. The results indicate that an ammonia-dedicated HCCI mode would misfire at a 22:1 compression ratio and an engine speed of 1500 rpm if the intake pressure and temperature are insufficient. Hydrogen addition can help overcome the misfire issue and reduce the intake pressure and temperature required for combustion initiation. However, higher hydrogen addition ratios decrease thermal efficiency and increase NOx emission levels. In lean NH3-H2 HCCI operation, NOx emissions are primarily driven by fuel-borne mechanisms and peak at an equivalence ratio of around 0.5. A higher hydrogen addition ratio should be avoided as it increases the risk of ringing, thereby reducing the maximum allowable equivalence ratio and engine load. As a result, a moderate hydrogen addition ratio, such as 20 %, is preferable for NH3-H2 HCCI engines. Additionally, an equivalence ratio of approximately 0.3 is optimal, balancing multiple performance indicators such as thermal efficiency, NOx emission levels, and engine operating stability. These findings suggest that the operating range of NH3-H2 HCCI engines is limited, making them more suitable for off-road applications, such as power generation.

The Green Energy Effect on an HCCI Engine from Used Cooking Oil-based Biodiesel from Malaysia

Emissions from internal combustion engines (ICEs) significantly impact the environment, leading continents worldwide to work towards reducing them. The industry is increasingly leaning towards electric powertrains. However, power plants still utilize ICEs as generators, contributing to global pollution. Consequently, ICE emissions are garnering international attention. Alternatives like the Homogeneous Charge Compression Ignition (HCCI) engine and biodiesel fuels are being explored. HCCI engines have not been extensively tested with Used Cooking Oil (UCO) biodiesel. This study investigates the performance and emissions of HCCI engines using UCO-based biodiesel. This study tested an air-cooled, single-cylinder, 4-stroke diesel engine operating at 3600 rpm with a displacement of 0.219 liters. The HCCI mode was activated during preheating and run at 2700 rpm under varying biodiesel blend percentages and intake temperatures. In HCCI mode, brake-specific fuel consumption (BSFC) increased, peaking at a 90°C intake temperature. Diesel fuel in-cylinder pressure reached a maximum of 81 bars at 90°C, decreasing to 79 bars at 70°C. The HCCI mode resulted in lower NOx, CO, and UHC emissions. Higher biodiesel blend ratios further reduced CO emissions. Raising the intake air temperature to 90°C lowered NOx emissions by 96.66%, from 150 ppm to 5 ppm. Using green energy sources as fuel in HCCI engines significantly reduced emissions in this study, suggesting their potential as a future fuel for advanced engines.

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 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.

Strategic combination of waste plastic/tire pyrolysis oil with biodiesel for natural gas-enriched HCCI engine: Experimental analysis and machine learning model

In this experiment, different combinations and blends based on 50% biodiesel and 50% pyrolysis oil were prepared to create 4 fuel samples for all tests. These samples were provided to the test engine operated on the conventional mode and homogeneous charge compression-ignition (HCCI) mode aiming to evaluate the performance, emission, and combustion characteristics of these modes. In the HCCI mode, a steady flow of 3 L per minute of compressed natural gas (CNG) was injected together with the air. As a result, preheated 50% Pongamia biodiesel/50% plastic pyrolysis oil combined with enriched CNG for the HCCI mode was found to be superior to those of other fuels according to performance, combustion, and emission characteristics although brake thermal efficiency was slightly lower than the conventional diesel engine. In addition, the performance and emission parameters of the HCCI engine were also predicted by using three machine learning models such as Decision Tree, Random Forest, and Support Vector Regression. Finally, Random Forest and Support Vector Regression approaches were recommended to predict the operation parameters of the HCCI engine with an accuracy level as high as nearly 99% in most instances, except for HC and CO with 80% and 90% of accuracy levels, respectively.

Quantification of φ-operating range with impact of exhaust gas recirculation under low-temperature combustion mode with polyoxymethylene dimethyl ether: A perspective study

Low-Temperature Combustion (LTC) especially Homogeneous charge compression ignition (HCCI) mode of combustion is a capable substitute mode of combustion to conventional diesel combustion (CDC) to provide better soot-NOx trade-off and HC-CO trade-off characteristics. The current study mainly focuses on the Exhaust Gas Recirculation (EGR) effects and equivalence ratio optimization on W20P20 (64% diesel, 16% WCO biodiesel, and 20% PODE) fuel along with exergy analysis in the HCCI mode of operation. The reason for inculcating exergy analysis in this research is to depict that low-temperature combustion provides a better heat transfer rate inside the cylinder. EGR has been varied in terms of 10%, 20%, and 30% in volume proportions along with the inlet fuel-air mixtures since, the fuel was injected through a pilot fuel injector in the inlet manifold. A novel factor in this research is considering both soot-NOx and HC-CO trade-off characteristics in optimizing the equivalence ratio with the influence of EGR over W20P20 fuel. The performance parameters such as BTE and BSEC show a mere decrement of about 6.67% and 29% of maximum with the influence of EGR while better combustion was found in terms of avoiding misfiring at a low equivalence ratio of 0.29–0.35 and knocking at a high equivalence ratio of 0.61–0.71 for W20P20 fuel. The operating range extension of the equivalence ratio was found with W20P20 fuel which further increased again with the increase in EGR addition. The emission limits of soot, NOx, CO, and HC particles were analyzed, in which the highest NOx reduction of 53% was obtained with 30% EGR irrespective of the equivalence ratio. The highest soot reduction was 61.85% with 20% EGR at a higher equivalence ratio. The highest HC reduction was 18% with 20% EGR at a lower equivalence ratio. The CO emissions seemed to reduce by 12% at a lower equivalence ratio while they increased by 47% at a higher equivalence ratio. The comparative results were studied for EGR influence with W20P20 fuel in the HCCI mode of combustion.

Replicating HCCI-like autoignition behavior: What gasoline surrogate fidelity is needed?

This work seeks to characterize the fidelity needed in a gasoline surrogate with the intent to replicate the complex autoignition behavior exhibited within advanced combustion engines, and specifically Homogeneous Charge Compression Ignition (HCCI). A low-temperature gasoline combustion (LGTC) engine operating in HCCI mode and a rapid compression machine (RCM) are utilized to experimentally quantify fuel reactivity, through autoignition and preliminary heat release characteristics. Fuels considered include a research grade E10 U.S. gasoline (RD5-87), three multi-component surrogates (PACE-1, PACE-8, PACE-20), and a binary surrogate (PRF88.4). Each fuel was studied at lean/HCCI-like conditions covering a wide range of temperatures and pressures that are representative of naturally aspirated to high boost engine operation. Detailed chemical kinetic modeling is also undertaken using a recently updated gasoline surrogate kinetic model to simulate the RCM experiments and to provide chemical insight into surrogate-to-surrogate differences.The LGTC engine experiments demonstrate nearly identical reactivity between PACE-20 and RD5-87 across studied conditions, while faster phasing is seen for both PACE-1 and PACE-8 due to their stronger intermediate- and low-temperature heat release (ITHR/LTHR) at naturally aspirated and boosted conditions, respectively. The RCM experiments reveal typical low-temperature, negative temperature coefficient (NTC) and intermediate-temperature autoignition behaviors at all pressure conditions for RD5-87, which are qualitatively reproduced by all surrogates. Quantitative discrepancies in both autoignition and preliminary heat release are observed for all surrogates, while their ability to replicate RD5-87 autoignition behavior follows the order of PACE-20 > PACE-1 > PACE-8 > PRF88.4. Excellent mapping is obtained between the LGTC engine and the RCM, where the engine pressure-time trajectories can be characterized by the regimes represented by the RCM autoignition isopleths. The kinetic model performs commendably when simulating both autoignition and preliminary heat release of PACE-20, while typically overpredicting ignition delay times for PACE-1, PACE-8 and PRF88.4 at high-pressure and low-temperature/NTC conditions. Sensitivity and rate of production (ROP) analyses highlight surrogate-to-surrogate differences in the governing chemical kinetics where n-pentane initiates rapid OH branching at a faster rate and an earlier timing for PACE-20 than iso-pentane does for PACE-1 and PACE-8, making it computationally more reactive than the other surrogates. The current study highlights the need to include non-standardized properties, such as the lean/HCCI-like autoignition characteristics, in addition to ASTM properties (e.g., RON, MON) as metrics of fuel reactivity and targets to be matched when formulating high-fidelity surrogates that fully capture gasoline advanced combustion behavior such as HCCI-like autoignition.

Experimental investigation on operating light-duty diesel engine using ethanol–gasoline blends in a homogeneous charge compression ignition combustion mode

The advanced diesel combustion mode of homogeneous charge compression ignition (HCCI) provides simultaneous lessening of soot and oxides of nitrogen (NOx) emissions. However, HCCI operations with low volatility and high reactivity diesel fuel require energy-intensive vaporizers and suffer from a restricted operating load range. In this work, high volatility, and low reactivity ethanol–gasoline blends were utilized as fuels in a port fuel injected light-duty diesel engine operated in HCCI mode to address this limitation. To study the effect of adding ethanol to the test fuels, its content was progressively increased from 10% to 60% by simultaneously reducing the gasoline content. 6% of an ignition improver, 2-ethylhexyl nitrate (2-EHN), was added to test fuels to attain stable HCCI combustion in the test engine at lower engine loads. A combined experimental and statistical approach was followed to characterize the HCCI engine combustion, performance and emissions. The impact of independent operating factors of ethanol–gasoline fuel blend composition and engine load on the various response parameters was estimated using multi-regression models developed based on the response surface method (RSM). The optimization of engine parameters was performed using the desirability approach of RSM to maximize performance and minimize emissions. The engine operating load range was extended from 23% (1.22 bar BMEP) to 86% (4.63 bar BMEP) with ethanol–gasoline–2-EHN-fuelled HCCI, which was a substantial improvement over the achievable load range only up to 38% (2.02 bar BMEP) with diesel-fuelled HCCI. All the multi-regression models developed were statistically significant at a 95% confidence level. The results showed that the indicated thermal efficiency improved, and soot and NOx emissions reduced with increased ethanol content in the test fuels. The test engine showed optimal working conditions when operated using 49% ethanol in the test fuels at 75% engine load. To benchmark the HCCI engine performance under optimal operating conditions, it was compared with conventional diesel combustion at 75% engine load. The NOx and soot emissions decreased by 76% and 98%, respectively, while indicated thermal efficiency increased by 20% for HCCI than conventional mode. The optimal fuel reactivity was determined at various engine loads by using the model equation developed for combustion phasing. According to the findings of this study, the fuel management strategy of using ethanol and gasoline blends is a viable method to enhance the performance and emission metrics of HCCI engines.

A comparative study of PODE/gasoline and n-heptane/gasoline in a spark-assisted homogeneous charge compression ignition engine with dual-injection strategies and EGR

Homogeneous charge compression ignition (HCCI) has potential to improve thermal efficiency for gasoline engine due to the similar formation of mixture between HCCI and traditional spark ignition mode. High reactivity fuel combined with gasoline is used to achieve HCCI combustion with a relative low compression ratio. Polyoxymethylene dimethyl ethers (PODE) is a kind of low-carbon fuels with unique molecule structure, which is beneficial for carbon neutral. The intermediate products of PODE are different from those of long-chain alkane such as n-heptane and diesel. In this paper, the difference in spark-assisted HCCI (SA-HCCI) combustion combined with spark ignition and EGR between PODE/gasoline and n-heptane/gasoline under different operating conditions were investigated. The results illustrated that PODE/gasoline was more suitable for SA-HCCI combustion due to the positive relation between thermal efficiency and gasoline percentage, which can significantly improve the thermal efficiency while suppressing knock. Although the cetane number of PODE is greater than the n-heptane, the SA-HCCI combustion was more violent fueled with n-heptane/gasoline than that of PODE/gasoline. Low NOx and PM emissions are achieved for SA-HCCI combustion especially for PODE/gasoline. The advancing spark timing reduced the incomplete combustion and shortened the combustion duration, thus reducing the THC and CO emissions, especially fueled with PODE/gasoline. Although a low EGR rate can slightly improve the THC and CO emissions, violent combustion can be significantly improved. In general, high efficiency and low emissions could be achieved by PODE/gasoline and spark ignition combined with EGR. The brake thermal efficiency for SA-HCCI combustion fueled with PODE/gasoline increased by 30% compared with DISI mode under the same loads.

Experimental investigation on effects of equivalence ratio on combustion with knock, performance, and emission characteristics of dimethyl ether fueled CRDI compression ignition engine under homogeneous charge compression ignition mode

This study deals with the effects of different equivalence ratios on combustion with a knock, performance, emissions of a DME fueled automotive CI engine under HCCI mode. The conventional common rail direct injection (CRDI) CI engine was modified to run with DME fuel (manifold injection) under HCCI mode. The experiments were conducted on the engine at different equivalence ratios at a constant speed of 1400 rpm. Two stages of combustion (low-temperature reaction (LTR) region and high-temperature reaction (HTR) region) were observed under HCCI mode. The LTR region occurs at the temperature range from 700 to 750 K. In contrast, the HTR region was at a temperature beyond 1000 K. The cyclic variations with the coefficient of variation (COV) of maximum in-cylinder pressure, indicated mean effective pressure with knock peak pressure and knocking intensity (KI) were analyzed for assessment of combustion stability. Based on the knocking intensity, the optimum equivalence ratio with controlled auto-ignition (CAI) was found as 0.55, with peak in-cylinder pressure of 70.87 bar and peak in-cylinder temperature of 1815 K. The COV for all the parameters and KI found below the limit value (COVlimit − 5% and knocklimit − 5 MW/m2) till 0.55 equivalence ratio and beyond the equivalence ratio, the knock occurred resulting in uncontrolled auto-ignition (UAI). Ultra-Low NOx (10–15 ppm) and zero smoke emissions with a considerable reduction in CO and HC emissions were observed at a higher equivalence ratio from DME fueled HCCI mode. However, CO and HC emissions were higher at lower equivalence ratio. This study shows that the simultaneous reduction of NOx and smoke emissions could be achieved in a DME fueled HCCI engine.

Effects of variations in fuel properties on a homogeneous charge compression ignited light-duty diesel engine operated with gasoline-isobutanol blends

Homogeneous charge compression ignition (HCCI) is a promising alternative combustion mode to conventional diesel combustion to achieve better engine performance and lower particulate matter and oxides of nitrogen emissions. In the present study, the experiments were performed in a modified light-duty diesel engine operated in port fuel injected HCCI mode with gasoline-isobutanol blends. All the experiments were performed at a constant engine speed of 1500 rpm and varying engine loads. The effects of variations in fuel properties on the achievable load range, engine performance improvement, and emission reduction were examined. The use of isobutanol, a gasoline-like high volatile, low reactivity, renewable fuel, help reduce fossil fuel dependency. A cetane improver, 2-ethyl hexyl nitrate (2-EHN), was added in a fixed proportion of 6 vol.% to all the fuel blends to attain stable HCCI combustion at lower engine loads. The volumetric proportion of isobutanol in the fuel blends was increased from 20% to 60%, while the gasoline proportion was correspondingly reduced. An algorithm to evaluate the ‘engine performance and emission indicator value’ was used to identify suitable fuel blend composition based on user-defined weights. Test results showed that the maximum achievable engine load was extended from 38% (of rated engine load) for diesel–fuelled HCCI to 70% (of rated engine load) for isobutanol-gasoline-2-EHN-fuelled HCCI. The indicated thermal efficiency improved with increased isobutanol in the fuel blends for a particular engine load. At 50% engine load, the indicated thermal efficiency improved by 40% for 60% isobutanol/ 34% gasoline/ 6% 2-EHN than 20% isobutanol/ 74% gasoline/6% 2-EHN. The HCCI combustion of isobutanol fuel blends produced very low oxides of nitrogen and soot emissions than conventional diesel combustion, and the indicated thermal efficiency was close to that of conventional diesel combustion at lower engine loads and improved at higher engine loads. At 70% engine load, the oxides of nitrogen and soot emissions were reduced by 69% and 96%, respectively, for HCCI combustion of 60% isobutanol/34% gasoline/6% 2-EHN than conventional diesel combustion. It was found that with an increase in engine load, the optimal fuel blend composition consisted of an increased concentration of isobutanol. Overall, the present study demonstrates that isobutanol is suitable for improving HCCI engine metrics.

Investigations on load range extension of a homogeneous charge compression ignited light-duty diesel engine operated with diisopropyl ether and gasoline blends

A major obstacle for commercial implementation of homogeneous charge compression ignition (HCCI) combustion mode is a narrow operating load range. Several thermal and fuel management strategies have been investigated so far to address the shortcomings of HCCI, among which fuel management strategies are generally more effective. The present study intends to utilize high volatile, optimum reactivity fuel to extend the operating load range of a light-duty diesel engine operated in HCCI mode. Experiments are conducted at the rated engine speed, and varying load conditions. The tested fuels include blends of gasoline and diisopropyl ether and the additive 2-ethyl hexyl nitrate (2-EHN). Diisopropyl ether is a low reactivity, and high volatile renewable fuel that has the potential to replace crude oil derived gasoline. In the fuel blends, the proportion of diisopropyl ether is increased from 10% to 60% by volume with a corresponding decrease in gasoline proportion. The results obtained are compared with diesel HCCI considered as the reference. The engine can operate only up to 38% of rated load (2.02 bar brake mean effective pressure) in diesel HCCI mode, which is increased up to 58% of rated load (3.08 bar brake mean effective pressure) with diisopropyl ether-gasoline-2-EHN fuel blends. An improvement in indicated thermal efficiency is observed upon increasing the diisopropyl ether content in the tested fuel blends. The oxides of nitrogen and smoke emissions are low in HCCI with all the fuel blends, while the unburned hydrocarbon and carbon monoxide emissions increase compared to diesel HCCI. Overall, the present research shows that diisopropyl ether is a potential fuel to achieve desired performance and emission targets in an HCCI engine.

NUMERICAL STUDY ON NOX EMISSION REDUCTION MECHANISM OF HCCI MARINE DIESEL ENGINE FOR IMO TIER III EMISSION LIMITS

With the advantages of ultra-low emissions of oxides of nitrogen (NOX) and high thermal efficiency, the homogeneous charge compression ignition (HCCI) mode applied to marine diesel engine is expected to be one of the technical solutions to meet the International Maritime Organization (IMO) MARPOL73/78 Convention-Annex VI Amendment Tier III requirement. According to the NOX chemical reaction mechanism, taking a marine diesel engine as the application object, the numerical study on the NOX formation characteristics of n-heptane for HCCI combustion process is performed. The results indicate that NO is usually the main component in the generation and emissions of NOX with the n-heptane HCCI mode. The combustor temperature plays more important role in the proportion of NO generation and emission. Compared with the experimental data of conventional marine diesel engine, the emission reduction rate of NOX can achieve an average of more than 95% in using HCCI technology.

Role of hydrogen in improving performance and emission characteristics of homogeneous charge compression ignition engine fueled with graphite oxide nanoparticle-added microalgae biodiesel/diesel blends

The development of low-temperature combustion models combined with the use of biofuels has been considered as an efficient strategy to reduce pollutant emissions like CO, HC. NOx, and smoke. Indeed, Homogeneous Charge Compression Ignition (HCCI) is the new approach to drastically minimize NOx emissions and smoke owing to the lower cylinder temperature and a higher rate of homogeneous A/F mixture as compared to compression ignition (CI) engines. The present research deal with the behavior analysis of a CI engine powered by diesel, Euglena Sanguinea (ES), and their blends (ES20D80, ES40D60, ES60D40, ES80D20). The experimental results revealed the highest brake thermal efficiency for ES20D80 although it decreased by 4.1% compared to diesel at normal mode. The average drop in HC, CO, and smoke was 2.1, 2.3, and 5.7% for ES20D80 as opposed to diesel fuel. Therefore, in the next stage, ES20D80 with various concentrations of graphite oxide (GO) nanoparticle (20, 40, 60, and 80 ppm) was chosen to carry out experiments in the HCCI mode, in which hydrogen gas was induced along with air through the intake pipe at a fixed flow rate of 3 lpm for the enrichment of the air-fuel mixture. As a result, the combination of hydrogen-enriched gas and GO-added ES20D80 in the HCCI mode showed similar performance to the CI engine but registered a major reduction of NOx and smoke emissions, corresponding to 75.24% and 53.07% respectively, as compared to diesel fuel at normal mode.

Important Contributions to Reducing Nitrogen Oxide Emissions from Internal Combustion Engines.

Nitrogen oxides are considered significant pollutants because of their effects on ecosystems and human health. The amount of NOx emitted by internal combustion engines can be reduced, mostly by acting on the conditions in which combustion takes place, respectively by lowering the peak flame temperature, reducing the excess of oxygen, etc. The homogeneous charge compression ignition (HCCI) engine represents a new technology that can simultaneously reduce NOx emissions and fuel consumption. This article presents these benefits of the HCCI engine by comparing the emissions and fuel consumption of a monocylinder engine when it is operated in a conventional way, with spark ignition, with those obtained when the engine is running in the HCCI mode. Moreover, since engine simulation has become an important tool for investigating the HCCI process and for developing new control strategies for it, this was used in this study to determine the effects of the exhaust gas recirculation on the combustion quality, respectively, on emissions.

Comparative study of energy losses related to the ring pack operation in homogeneous charge compression ignition and spark ignition combustion

Low-temperature combustion in homogeneous charge compression ignition (HCCI) engine is one of the most promising technologies allowing to meet future emission targets for internal combustion engines. Whereas majority of research is centred on combustion itself, this paper for the first time points out the piston's energy losses induced by friction and blow-by in HCCI engine with negative valve overlap. The energy losses for HCCI and spark ignition (SI) operating modes were compared and thoroughly analysed with the use of the ring pack model. The input data for the simulations came from measurements made on a single-cylinder research engine capable of dual-mode combustion. The energy losses associated with friction of the rings against the cylinder varied from 8.2% of the indicated energy at the lowest load to 2.2% at the highest load tested, and were higher than in the SI mode by approximately 7%. The losses due to the gas leakage through the ring pack in the HCCI mode varied from 8% to 3.3%, respectively, and these losses were about twice as high as in the SI engine. The results demonstrated that energy losses due to blow-by are comparable with the friction losses of the rings, which are usually regarded as the prime source of inefficiency.

Parametric investigation on hydrogen driven homogeneous charge compression ignition mode with advanced diesel injection using chemical kinetics based numerical model

In the present study, a numerical model based on chemical kinetics was developed to investigate the effect of different parameters on characteristics of hydrogen diesel homogeneous charge compression ignition (HDHCCI) mode. The results showed that the combustion process was retarded with diminished cool flame as increasing hydrogen energy share (HES) due to reduction of H2O2, H2O and OH radicals with hydrogen addition. Thus, it increased the indicated thermal efficiency (ITE) and decreased the indicated specific energy consumption (ISEC). The levels of NOx and soot emissions were reduced by 22% and 63% at maximum HES. A spray angle of 10° decreased the total fuel impingement compared with a spray angle of 74° because of improvement in air-fuel mixing phenomena. Incomplete combustion was recovered at HES of 25% when increasing the charge temperature or adapting the twin-pulse in HDHCCI mode, consequently the ITE was improved with a decrease in ISEC.

Experimental investigation of strategies to enhance the homogeneous charge compression ignition engine characteristics powered by waste plastic oil

In the present-day scenario, the regulations over vehicle emissions are highly stringent, and the manufacturers are struggling to satisfy the emission norms. Waste plastic oil (WPO) powered conventional compression ignition (CI) engine discharge higher oxides of nitrogen emission. The utilization of WPO as a sole fuel in homogeneous charge compression ignition (HCCI) engine would satisfy both energy demand and emission norms. The present study demonstrates the effects of different intake air temperatures (IAT) and injection pressures (IP) of WPO on the HCCI engine’s performance and combustion characteristics. The results revealed that the WPO fueled CI engine showed greater BTE when correlated to WPO powered HCCI engine. In the HCCI mode of operation, the elevated IAT led to the advanced start of combustion (SOC). It shortened the combustion due to an increase in post-combustion temperature and cylinder pressure. WPO operated homogeneous charge mode with IAT of 90 °C resulted in better BTE and lesser unburnt hydrocarbon (UBHC), smoke, and carbon monoxide (CO) emission than IAT atmospheric conditions. The HCCI engine with elevated IAT of 80 °C, 90 °C, and 100 °C drastically reduced the NOx emission by 45.5%, 41.9%, and 40.04% than standard CI engine fueled with WPO+- respectively. Among various IPs of WPO, IP of 8 bar revealed 3.08% higher BTE with 11.2%, 16.6%, 14.7% decrease in CO, UBHC, and smoke emission, respectively. At the optimum condition of IP and IAT in the HCCI engine, the BTE was closer to that of the WPO powered CI engine, and also ultra-lean NOx and smoke emissions were noticed.

Performance and emission characteristics of a methane fuelled HCCI engine at various injection location and operating speed

Methane is a promising alternative fuel for stationary IC engines due to its ease of production and superior combustion properties. However, methane cannot be used independently in Homogeneous Charge Compression Ignition (HCCI) engines due to its high auto-ignition temperature. Another contributing factor is its lesser cetane number compared to its alternatives. A high reactivity fuel such as Di-Ethyl Ether (DEE) has to be used as an ignition improver by virtue of its high cetane number. In this study, methane and DEE are used as primary and secondary fuels respectively in HCCI mode. A mixture of methane and air along with the ignition improver DEE is injected in two locations – the first location being behind the inlet port and the second location being the manifold that is situated 10 cm away from the inlet port during suction stroke. The performance and emission of the engine are compared for both modes of DEE injection with torque varying from 10% to 90% of rated load and speeds ranging between 1800 rpm and 1900 rpm. A constant methane flow rate of 12 lpm is used. Port injection provides better thermal efficiency at 1800 rpm while manifold injection is observed to be superior at 1900 rpm. HC and CO emissions are lower with manifold injection at 1800 rpm whereas NOx emissions are comparable for both modes. Smoke and NOx emissions are lower with manifold injection at 1900 rpm.

Comparison of the hydrogen powered homogeneous charge compression ignition mode with multiple injection schedules and the dual fuel mode using a twin-cylinder engine

The present work discusses the influence of injection schedules in hydrogen diesel homogeneous charge compression ignition (HDHCCI) mode, the experiments were carried out in three distinct diesel injection schedules like single pulse, double pulse and multi-pulse at low load operation. The maximum reachable hydrogen energy shares (HES) are 27.46%, 26.97% and 39.96% for a single pulse, double pulse and multi-pulse respectively. For almost all HES levels, the single pulse and double pulse HDHCCI mode provided ultra-low NO emission when compared with hydrogen diesel dual fuel (HDDF) mode. The multi-pulse injection increased the brake thermal efficiency (BTE) compared with single pulse and double pulse injection, since the timing of injection pulse 3 (IP3) in multi-pulse significantly altered the combustion characteristics of HDHCCI mode. Locating the IP3 in the window of 30–40 °BTDC (before cool flame) enhanced the BTE and reduced the brake specific energy consumption (BSEC) of the engine.