Spark ignition to homogeneous charge compression ignition mode transition study: a new modelling approach

<div class="htmlview paragraph">A naturally aspirated in-line six-cylinder 2.9-litre Volvo engine is operated in Homogeneous Charge Compression Ignition (HCCI) mode, using camshafts with low lift and short duration generating negative valve overlap. This implementation requires only minor modifications of the standard SI engine and allows SI operation outside the operating range of HCCI. Standard port fuel injection is used and pistons and cylinder head are unchanged from the automotive application. A heat exchanger is utilized to heat or cool the intake air, not as a means of combustion control but in order to simulate realistic variations in ambient temperature. The combustion is monitored in real time using cylinder pressure sensors.</div> <div class="htmlview paragraph">HCCI through negative valve overlap is recognized as one of the possible implementation strategies of HCCI closest to production. However, for a practical application the intake temperature will vary both geographically and from time to time. It is therefore very important to gain knowledge of how this variation affects the combustion process.</div> <div class="htmlview paragraph">The operating range in HCCI mode for this specific engine stretches from 650 rpm to 4000 rpm and from 1 bar IMEP to 4 bar IMEP. The emissions of NO<sub>x</sub> are approximately two orders of magnitude lower in HCCI mode compared to SI mode. The emissions of CO are slightly lower while the emissions of HC are slightly higher for HCCI operation. When run in HCCI mode the engine's efficiency is improved throughout the operating range by as much as 10 percentage units compared to SI operation. The effect of inlet air temperature variation on HCCI combustion through negative valve overlap is insignificant when the engine runs well inside of the HCCI operating range. The effect is however prominent when the engine is operated close to the border of the operating range.</div>

Diethyl ether as an ignition improver for biogas homogeneous charge compression ignition (HCCI) operation - An experimental investigation

Evaluation of Homogeneous Charge Compression Ignition (HCCI) autoignition development through chemiluminescence imaging and Proper Orthogonal Decomposition

Homogeneous Charge Compression Ignition (HCCI) combustion in a small-scale engine (25 cc) was experimentally examined. Historically, HCCI combustion has been studied in engines sized for passenger vehicles and trucks (approximately 500 cc and larger). HCCI combustion in large-scale engines is characterized by higher efficiency than SI and CI combustion. High rates of heat flux, due to large surface area to volume ratio and engine body material, initially prevented the small-scale engine from operating in HCCI mode. The high level of heat transfer was overcome and sustained small-scale HCCI operation was achieved with n-heptane fuel. Large-scale HCCI engines utilize ultralow equivalence ratios to achieve high efficiencies. The small-scale HCCI engine could not operate with equivalence ratios lower than 0.73. Performance characteristics including power, efficiency, and NOx emissions of the small-scale HCCI engine were poorer than when operated in SI mode. Recommendations to overcome high rates of heat flux and increase small-scale HCCI engine efficiency are presented.

Homogeneous Charge Compression Ignition (HCCI) is a new combustion mode with higher thermal efficiency and lower emission. With the recent development of experimental and theoretical investigations, HCCI operation for high cetane number fuels has attracted more attention. As a reference fuel, n-heptane is very easy to be ignited for high cetane number and shows obviously two-stage heat release in homogeneous charge compression ignition process due to chemical properties. HC, CO and NOx emissions of n-heptane HCCI combustion with intake temperature and excess air coefficient are studied in this paper. Intake temperature and excess air coefficient have a great impact on HCCI combustion and provide important approaches to widen HCCI operating range.

Scientists are interested in a homogeneous charge compression ignition combustion model (HCCI) to replace a conventional combustion model on an internal combustion engine.This combustion model has the same performance as a direct-injection gasoline engine and the same type of ignition as a diesel engine.However, the NOx emission component is significantly reduced, while the smoke level is almost zero.With this combustion model, it's perfectly capable of meeting emissions requirements without having to be equipped with an additional emission after-treatment system.In this study, the author converted a traditional one-cylinder diesel engine into a new engine based on HCCI mode.In order to be able to work in HCCI mode, it is necessary to modify the engine's parameters, such as reducing the compression ratio, equipping it with a port fuel supply system, or combining air heating and exhaust recirculation systems.The study results have shown that the converted engine can operate according to the principle of HCCI in low load conditions of up to 30%.The combustion characteristics and engine operation parameters before and after conversion to HCCI mode are tested and evaluated on the engine test bed.Experimental research to quantify and assess the engine's HCCI operating mode and construct a set of control parameters for setting and widening the working regime in HCCI mode.

Homogenous Charge Compression Ignition (HCCI) is an alternative to Spark Ignited (SI) combustion, which can provide part-load efficiencies as high as compression ignition engines and energy densities as high as SI engines, without high levels of NOx or Particulate Matter (PM). The principle of operation involves reaching the thermal oxidization barrier of a homogeneous air-fuel mixture. This combustion practice is enabled by diluting then compressing the mixture with the Trapped Residual Gases (TRG) to dilute the initial charge thus keeping combustion temperatures down. Introduction of exhaust gasses in the mixture can be achieved by the use of early exhaust valve closure and late inlet valve opening. The charge is well mixed avoiding particulate emissions, and by using exhaust gasses for load regulation the need for throttled operation is removed allowing the realization of high efficiencies, low pumping losses and a resulting 15 - 20 % improvement in fuel economy. One of the major disadvantages of HCCI is that it can only be used at part load conditions, and so it has been proposed that a 'hybrid mode' engine operation strategy could be used, where the engine uses SI operation at cold start, high load and idle. This demands a closed loop feedback control signal to give a seamless transition between SI (where Start of Combustion (SOC) is dictated by the spark plug) and HCCI (where SOC is unknown). This paper investigated the use of an ion current sensor to accurately predict the Peak Pressure Position (PPP) and Peak Pressure Magnitude (PPM). This is achieved with the mathematically simple and computationally efficient approach of linear regression. This technique can be used between engine cycles so adjustments can be made to engine strategies to compensate for difficult conditions. The results showed that there is a definite correlation between the two signals and that the ion current can be used to control the engine during HCCI mode. Finally a good balance between computation time and accuracy was obtained using 20 cycles.

Multimode combustion (MMC) concepts using homogeneous charge compression ignition (HCCI) gasoline combustion at low loads and spark assisted compression ignition (SACI) gasoline combustion at medium loads have the potential for improved fuel efficiency relative to spark ignition (SI) gasoline combustion. Two MMC concepts are compared in this paper with respect to fuel efficiency and tailpipe NOx emissions. The first concept uses stoichiometric HCCI and SACI to allow standard three-way catalyst (TWC) operation. The second concept also uses HCCI and SACI, but cycles between lean and rich combustion and uses a TWC with increased oxygen storage capacity (OSC) for potentially even greater fuel efficiency improvement. This paper performs a preliminary comparison of the two MMC concepts by analyzing two scenarios: (1) cycling between stoichiometric HCCI at 2 bar BMEP (brake mean effective pressure) and stoichiometric SACI at 3 bar BMEP, and (2) cycling between lean HCCI at 2 bar BMEP and rich SACI at 3 bar BMEP. The effects of excess oxygen ratio during HCCI operation and the frequency of oxygen depletion events on TWC performance and fuel efficiency are investigated. Results show that MMC lean/rich cycling can achieve better fuel efficiency than stoichiometric HCCI/SACI cycling. NOx emissions are moderately higher, but may still be low enough to meet current and future emission regulations.

<div class="htmlview paragraph">Homogeneous Charge Compression Ignition (HCCI) is effective for the simultaneous reduction of soot and NOx emissions from diesel engine. In general, high octane number and volatility fuels (gasoline components or gaseous fuels) are used for HCCI operation, because very lean mixture must be formed during ignition delay of the fuel. However, it is necessary to improve fuel injection systems, when these fuels are used in diesel engine.</div> <div class="htmlview paragraph">The purpose of the present study is the achievement of HCCI combustion in DI diesel engine without the large-scale improvements of engine components. Various high octane number fuels are mixed with diesel fuel as a base fuel, and the mixed fuels are directly applied to DI diesel engine. At first, the cylinder pressure and heat release rate of each mixed fuel are analyzed. The ignition delay of HCCI operation decreases with an increase in the operation load, although that of conventional diesel operation does not almost varied. In addition, the mixed fuel containing much high volatility fuel produces the higher peak of heat release rate of premixed combustion.</div> <div class="htmlview paragraph">The exhaust emissions (CO, CO<sub>2</sub>, THC, NOx, PM) in case of each mixed fuel are measured. Low NOx emission can be achieved by HCCI operation using the mixed fuels despite low volatility of base fuel. However, PM emission is relatively high in case of HCCI operation, and then PM is separated into SOF and ISOF. As a result, it can be confirmed that the high PM emission is derived from the increase in SOF, and the high SOF emission results from the base fuel in the mixed fuels.</div>

<div class="htmlview paragraph">Homogenous charge compression ignition (HCCI) has been identified as a promising way to increase the efficiency of the spark-ignited engine, while maintaining low emissions. The challenge with HCCI combustion is excessive pressure rise rate, quantified here with Ringing Intensity. Turbocharging enables increased dilution of the charge and thus a reduction of the Ringing Intensity. The engine used is an SI four cylinder base with 2.2<i>L</i> displacement and is equipped with a turbocharger. Combustion phasing control is achieved with individual intake/ exhaust cam phasing. Fuel injection with spray guided design is used. Cycle resolved combustion state is monitored and used for controlling the engine either in closed or open loop where balancing of cylinder to cylinder variations has to be done to run the engine at high HCCI load. When load is increased the NOx levels rise, the engine is then run in stoichiometric HCCI mode to be able to use a simple three-way catalyst. The fuel used is 95 RON pump gasoline and injection strategies are evaluated in order to maintain low soot levels and high efficiency. Limitations and benefits on operating range are examined between 1000 and 3000 rpm. This paper investigates how to extend the HCCI range and how to reduce the high pressure rise rate with: increased boost from turbocharging, external EGR and different injection strategies. A higher boost pressure was found to extend the load range. It is shown that the limitation from high RI, NOx or soot is not the same in all engine speed and load points. By turbocharging the engine in HCCI mode there is greater flexibility to increase the range of practical operating points.</div>

Advanced combustion has progressively become a topic of interest as government regulations have stringently reduced the allowable limits of engine-out emissions from internal combustion engines. Advanced combustion can typically be classified as homogeneous charge compression ignition (HCCI) or premixed charge compression ignition (PCCI). In HCCI combustion, a well mixed fuel and air solution is spontaneously combusted, thus providing a homogeneous burn throughout the combustion process. By having an evenly distributed, homogeneous burn, fuel economy is not only significantly increased, but both oxides of nitrogen (NO x) and particulate matter (PM) can drastically be reduced from that of conventional combustion. HCCI has the ability to incorporate the low PM emissions of a spark ignited (SI) engine as well as the high thermal efficiency of a compression ignited (CI) engine. Similar to HCCI, PCCI offers low NO x and PM within a part load operating range with a quasi-homogenous fuel and air mixture. Other than identifying HCCI or PCCI as having very limited NOx and PM production, in-cylinder combustion techniques can also be utilized to characterize these forms of advanced combustion.;An experimental study was performed at West Virginia University (WVU) in an attempt to achieve HCCI or PCCI operation by implementing a number of engine control strategies using a range of fuels with varying fuel properties. The test engine, a GM 1.9L, was incorporated with an ECU controller capable of controlling engine operating parameters such as rail pressure, start of injection (SOI), fuel quantity injected and exhaust gas recirculation (EGR) valve position. Piezoelectric crystal pressure transducers were introduced into each cylinder via glow plug adapters and a custom WVU data acquisition system was used to evaluate in-cylinder combustion parameters. Testing was performed at a 2100 RPM, 53 N-m, steady-state set point using an engine dynamometer. By implementing high levels of EGR, NOx emissions were reduced nearly 90% due to lower cylinder pressures and increased ignition delay. PM emissions were also reduced by 15% within a specific EGR range due to increased mixing time available from a longer ignition delay as verified by in-cylinder pressure, heat release rate and mass fraction burned data. Fuel characteristics were compared at a single operating condition and at an optimized control strategy with increased thermal efficiency, for low NOx and PM emissions that were determined from a range of EGR, pilot injection, main injection, rail pressure and fuel split sweeps. The cetane number (CN) of the fuel

Vapour-phase and particulate-bound PAHs profile generated by a (SI/HCCI) engine from a winter grade commercial gasoline fuel

<div class="section abstract"><div class="htmlview paragraph">The carbon-neutral biodiesel is a promising renewable substitute for fossil diesel that renders the traditional oxides of nitrogen-particulate matter (NO<sub>x</sub>-PM) trade-off into a unidirectional NO<sub>x</sub> control problem. Low-temperature combustion (LTC) modes such as homogenous charge compression ignition (HCCI) are attractive for obtaining ultra-low NO<sub>x</sub> and PM emissions. Studies on utilizing biodiesel fuel for HCCI combustion mode are sparsely available. Moreover, biodiesel emulsions in the HCCI combustion mode have not been attempted so far. Based on this premise, the present work explored the potential to utilize biodiesel and its emulsions having 20% and 25% water by volume under HCCI operating conditions. Biodiesel was prepared from a non-edible Karanja oil. The biodiesel emulsions were prepared using a heated magnetic stirrer apparatus with 3% by volume of the raw Karanja oil as a surfactant. A production light-duty diesel engine is modified to run in external mixture preparation based HCCI mode. An air-preheater and a fuel vaporizer aid in vaporizing the low volatile biodiesel injected into the inner surface of the vaporizer at 300 bar pressure using a common rail direct injection (CRDI) system. The engine compression ratio was fixed at 15, the maximum operable value with biodiesel. The results show that the engine could be operated only up to 20% of the rated load with biodiesel. With biodiesel-water emulsion, 30% of the rated load could be achieved. The maximum cylinder pressure was higher, and the heat release rate was advanced with emulsions compared to neat biodiesel. The brake specific fuel consumption was reduced by 35%, and the brake thermal efficiency increased by 2.4%, along with ultra-low NO<sub>x</sub> and smoke emissions with emulsions. The present study shows the potential to utilize biodiesel-water emulsions in HCCI mode with reduced exhaust emissions. Suitable charge dilution methods must be adopted to extend the HCCI operating load range with emulsions.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Gasoline direct injection (GDI) technology is admitted to be one of the most effective measures to improve the fuel economy for the spark ignition (SI) engines. Homogeneous Charge Compression Ignition (HCCI) combustion has advantages of low fuel consumption and ultra low NO<sub>x</sub> emissions. But the difficulty in the autoignition control and the narrow operation region inhibit the practical application of this technology. A hybrid combustion mode which combines SI mode and HCCI mode in separated working regions was regarded as a promising technology for HCCI engines. In addition, monitoring and providing feedback to the in-cylinder combustion characteristics is generally considered to be an effective method to improve and to optimize the combustion process. A lot of combustion information is included in the ion current generated by the in-cylinder combustion, and hence the ion current detection technique is considered to be a potential combustion feedback method. A strategy used in the SI/HCCI combustion mode switch based on ion current was established and experimented in a GDI-HCCI engine assisted by negative valve overlap (NVO). During the combustion mode switch process, by adjusting the key factors within the switch process, such as injection mass, injection timing and throttle opening, the switch process was optimized. The optimized SI-HCCI mode switch, not only the smoothness was improved, cylinder pressure amplitude, indicated mean efficiency pressure (IMEP), HC and NO<sub>x</sub> emissions were stable, but also the fuel economy and the emission performance were promoted.</div></div>

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.