Application of Variable Valve Actuation Strategies and Direct Gasoline Injection Schemes to Reduce Combustion Harshness and Emissions of Boosted HCCI Engine

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Jacek Hunicz ◽  
Maciej Mikulski
Keyword(s):  
Pressure Rise ◽  
Operating Conditions ◽  
Exhaust Valve ◽  
Boost Pressure ◽  
Pressure Reduction ◽  
Intake Valve ◽  
Valve Timing ◽  
Hcci Engine ◽  
Auto Ignition ◽  
The Impact

The present study investigates various measures to reduce pressure rise rates (PRRs) in a residual-affected homogeneous charge compression ignition (HCCI) engine. At the same time, the impact of those measures on efficiency and emissions is assessed. Experimental research was performed on a single cylinder engine equipped with a fully flexible valve train mechanism and direct gasoline injection. The HCCI combustion mode with exhaust gas trapping was realized using negative valve overlap (NVO) and fuel reforming, achieved via the injection of a portion of fuel during exhaust recompression. Three measures are investigated for the PRR control under the same reference operating conditions, namely: (i) variable intake and exhaust valve timing, (ii) boost pressure adjustment, and (iii) split fuel injection to control the amount of fuel injected for reforming. Variable exhaust valve timing enabled control of the amount of trapped residuals, and thus of the compression temperature. The reduction in the amount of trapped residuals, at elevated engine load, delays auto-ignition, which results in a simultaneous reduction of pressure rise rates and nitrogen oxides emissions. The effects of intake valve timing are much more complex because they include the variability in the amount of intake air, the thermodynamic compression ratio, as well as the in-cylinder fluid flow. It was found, however, that both early and late intake valve openings (IVOs) delay auto-ignition and prolong combustion. Additionally, the reduction of the amount of fuel injected during exhaust recompression further delays combustion and reduces combustion rates. Intake pressure reduction has by far the largest effect on peak pressure reduction yet is connected with excessive NOX emissions. The research successfully identifies air-path and injection techniques, which allow for the control of combustion rates and emissions under elevated load regime.

Application of Variable Valve Actuation Strategies and Direct Gasoline Injection Schemes to Reduce Combustion Harshness and Emissions of Boosted HCCI Engine

2018 ◽  
Author(s):  
Jacek Hunicz ◽  
Maciej Mikulski
Keyword(s):  
Pressure Rise ◽  
Operating Conditions ◽  
Exhaust Valve ◽  
Boost Pressure ◽  
Pressure Reduction ◽  
Intake Valve ◽  
Valve Timing ◽  
Hcci Engine ◽  
Auto Ignition ◽  
The Impact

One of the pending issues regarding Homogeneous Charge Compression Ignition (HCCI) engines is high load operation limit constrained by excessive pressure rise rates (PRRs). The present study investigates various measures to reduce combustion harness in a residual-affected HCCI engine. At the same time, the impact of those measures on efficiency and emissions is assessed. Experimental research was performed on a single cylinder engine equipped with a fully-flexible valvetrain mechanism and direct gasoline injection. The HCCI combustion mode with exhaust gas trapping was realized using negative valve overlap and fuel reforming, achieved via the injection of a portion of fuel during exhaust re-compression. Three measures are investigated for the PRR control under the same reference operating conditions, namely: (i) variable intake and exhaust valve timing, (ii) boost pressure adjustment and (iii) split fuel injection to control the amount of fuel injected for reforming. Variable exhaust valve timing enabled control of the amount of trapped residuals, and thus of the compression temperature. The reduction in the amount of trapped residuals, at elevated engine load, delays auto-ignition, which results in a simultaneous reduction of pressure rise rates and nitrogen oxides emissions. The effects of intake valve timing are much more complex, because they include the variability in the amount of intake air, the thermodynamic compression ratio as well as the in-cylinder fluid flow. It was found, however, that both early and late intake valve openings delay auto-ignition and prolong combustion. Additionally, the reduction of the amount of fuel injected during exhaust re-compression further delays combustion and reduces combustion rates. Intake pressure reduction has by far the largest effect on peak pressure reduction yet is connected with excessive NOx emissions. The research successfully identifies air-path and injection techniques, which allow for the control of combustion rates and emissions under elevated load regime, thus shorting the gap towards the real-world application of HCCI concepts.

Modeling the Effects of Variable Intake Valve Timing on Diesel HCCI Combustion at Varying Load, Speed and Boost Pressures

2005 ◽  
Author(s):  
Caroline L. Dougan ◽  
Song-Charng Kong ◽  
Rolf D. Reitz
Keyword(s):  
Operating Conditions ◽  
Boost Pressure ◽  
Combustion Control ◽  
Intake Valve ◽  
Valve Timing ◽  
Detailed Chemical Kinetics ◽  
Available N ◽  
Hcci Combustion ◽  
Auto Ignition ◽  
Variable Valve

It is well known that homogeneous charge compression ignition (HCCI) operated engines have the potential to provide the efficiency of a typical diesel engine, but with very low NOx and Particulate Matter (PM) emissions. One of the main challenges with this type of engine, however, is that it can be difficult to control the combustion event, especially at high loads. The development of Variable Valve Timing (VVT) technology may offer an important advantage in the ability to control HCCI combustion. This work investigates the potential of using late intake valve closure times to delay auto-ignition and to expand the HCCI operation range through proper combustion control. A multi-dimensional KIVA/Chemkin model is used in conjunction with detailed chemical kinetics, based on an available n-heptane mechanism. The model is used to evaluate the effectiveness of late intake valve times as load, speed, and boost pressure conditions are varied. Furthermore, a larger understanding of diesel HCCI combustion is sought by investigating the major parameters affecting combustion control under these various operating conditions.

Modeling the Effects of Variable Intake Valve Timing on Diesel HCCI Combustion at Varying Load, Speed, and Boost Pressures

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
C. L. Genzale ◽  
S.-C. Kong ◽  
R. D. Reitz
Keyword(s):  
Operating Conditions ◽  
Effective Control ◽  
Intake Valve ◽  
Valve Timing ◽  
Detailed Chemical Kinetics ◽  
Hcci Combustion ◽  
Wide Range ◽  
Particulate Matter Emissions ◽  
Charge Mixture ◽  
Ignition And Combustion

Homogeneous charge compression ignition (HCCI) operated engines have the potential to provide the efficiency of a typical diesel engine, with very low NOx and particulate matter emissions. However, one of the main challenges with this type of operation in diesel engines is that it can be difficult to control the combustion phasing, especially at high loads. In diesel HCCI engines, the premixed fuel-air charge tends to ignite well before top dead center, especially as load is increased, and a method of delaying the ignition is necessary. The development of variable valve timing (VVT) technology may offer an important advantage in the ability to control diesel HCCI combustion. VVT technology can allow for late intake valve closure (IVC) times, effectively changing the compression ratio of the engine. This can decrease compression temperatures and delay ignition, thus allowing the possibility to employ HCCI operation at higher loads. Furthermore, fully flexible valve trains may offer the potential for dynamic combustion phasing control over a wide range of operating conditions. A multidimensional computational fluid dynamics model is used to evaluate combustion event phasing as both IVC times and operating conditions are varied. The use of detailed chemical kinetics, based on a reduced n-heptane mechanism, provides ignition and combustion predictions and includes low-temperature chemistry. The use of IVC delay is demonstrated to offer effective control of diesel HCCI combustion phasing over varying loads, engine speeds, and boost pressures. Additionally, as fueling levels are increased, charge mixture properties are observed to have a significant effect on combustion phasing. While increased fueling rates are generally seen to advance combustion phasing, the reduction of specific heat ratio in higher equivalence ratio mixtures can also cause noticeably slower temperature rise rates, affecting ignition timing and combustion phasing. Variable intake valve timing may offer a promising and flexible control mechanism for the phasing of diesel HCCI combustion. Over a large range of boost pressures, loads, and engine speeds, the use of delayed IVC is shown to sufficiently delay combustion in order to obtain optimal combustion phasing and increased work output, thus pointing towards the possibility of expanding the current HCCI operating range into higher load points.

Computational Analysis of an Early Direct Injected HCCI Engine with Turbocharger Using Bio Ethanol and Diesel Blends

2015 ◽  
Vol 812 ◽  
pp. 70-78
Author(s):  
S. Natarajan ◽  
A.U. Meeanakshi Sundareswaran ◽  
S. Arun Kumar ◽  
N.V. Mahalakshmi
Keyword(s):  
Chemical Kinetics ◽  
Computational Analysis ◽  
Reaction Path ◽  
Chemical Species ◽  
Operating Conditions ◽  
Injection Time ◽  
Engine Operation ◽  
Hcci Engine ◽  
Hcci Combustion ◽  
Auto Ignition

In this paper the work deals with the computational analysis of early direct injected HCCI engine with turbocharger using the CHEMKIN-PRO software. The computational analysis was carried out in the base of auto ignition chemistry by means of reduced chemical kinetics. For this study the neat diesel and Bio ethanol diesel blend (E20) were used as fuel. The inlet pressure was increased to 1.2 bar to simulate the turbocharged engine operation. The injection time was advanced to 18° before top dead centre (BTDC) i.e., 5° BTDC than normal injection time of 23° BTDC. The equivalence ratio was kept at 0.6 (ɸ=0.6) and the combustion, emission characteristics and chemical kinetics of the combustion reaction were studied. Since pressure and temperature profiles plays a very important role in reaction path at certain operating conditions, an attempt had been made here to present a complete reaction path investigation on the formation/destruction of chemical species at peak temperature and pressure conditions. The result showed that main draw backs of HCCI combustion like higher levels of unburned hydrocarbon emissions and carbon monoxide emissions are reduced in the turbocharged operation of the HCCI engine when compared to normal HCCI engine operation without turbocharger.

Combustion and emission characteristics of a homogeneous charge compression ignition engine

2005 ◽  
Vol 219 (9) ◽  
pp. 1133-1139 ◽  
Author(s):  
Hu Tiegang ◽  
Liu Shenghua ◽  
Zhou Longbao ◽  
Zhu Chi
Keyword(s):  
Heat Release ◽  
Homogeneous Charge Compression Ignition ◽  
Cetane Number ◽  
Pressure Rise ◽  
Operating Conditions ◽  
Emission Characteristics ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Hcci Engine ◽  
Homogeneous Charge

Dimethyl ether (DME) is a kind of fuel with high cetane number and low evaporating temperature, which is suitable for a homogeneous charge compression ignition (HCCI) engine. The combustion and emission characteristics of an HCCI engine fuelled with DME were investigated on a modified single-cylinder engine. The experimental results indicate that the HCCI engine combustion is a two-stage heat release process. The engine load or air-fuel ratio has significant effects on the maximum cylinder pressure and its position, the shape of the pressure rise rate and the heat release rate. The engine speed has little effect. A DME HCCI engine is smoke free, with zero NOx and low hydrocarbon and CO emissions under the operating conditions of 0.25–0.30 MPa brake mean effective pressure.

Effects of EGR and Boost Pressure on Reactivity Controlled Compression Ignition (RCCI) Engine at High Load Operating Conditions

2014 ◽  
Author(s):  
Yifeng Wu ◽  
Rolf D. Reitz
Keyword(s):  
Peak Pressure ◽  
Pressure Rise ◽  
High Load ◽  
Operating Conditions ◽  
Boost Pressure ◽  
Compression Ignition ◽  
Effective Pressure ◽  
Reactivity Controlled Compression Ignition ◽  
Brake Mean Effective Pressure ◽  
Diesel Injection

Reactivity Controlled Compression Ignition (RCCI) at engine high load operating conditions is investigated in this study. The effects of EGR and boost pressure on RCCI combustion were studied by using a multi-dimensional computational fluid dynamics (CFD) code. The model was first compared with a previous CFD model, which has been validated against steady-state experimental data of gasoline-diesel RCCI in a multi-cylinder light duty engine. An RCCI piston with a compression ratio of 15:1 was then proposed to improve the combustion and emissions at high load. The simulation results showed that 18 bar indicated mean effective pressure (IMEP) could be achieved with gasoline-diesel RCCI at an EGR rate of 35 % and equivalence ratio of 0.96, while the peak pressure rise rate (PPRR) and engine combustion efficiency could both be controlled at reasonable levels. Simulations using both early and late direct-injection (DI) of diesel fuel showed that RCCI combustion at high load is very sensitive to variations of the exhaust gas recirculation (EGR) amount. Higher IMEP is obtained by using early diesel injection, and it is less sensitive to EGR variation compared to late diesel injection. Reduced unburned hydrocarbon (HC), carbon monoxide (CO), soot and slightly more nitrogen oxides (NOx) emissions were seen for early diesel injection. HC, CO and soot emissions were found to be more sensitive to EGR variation at late diesel injection timings. However, there was little difference in terms of peak pressure, efficiencies, PPRR and phasing under varying EGR rates. The effect of boost pressure on RCCI at high load operating conditions was also studied at different EGR rates. It was found that combustion and emissions were improved, and the sensitivity of the combustion and emission to EGR was reduced with higher boost pressures. In addition, cases with similar combustion phasing and reasonable PPRR were analyzed by using an experimentally validated GT-Power model. The results indicated that although higher IMEP was generated at higher boost pressures, the brake mean effective pressure (BMEP) was similar compared to that obtained with lower boost pressures due to higher pumping losses.

Qualification of Gasket Performance for Vacuum Applications

2010 ◽  
Author(s):  
Walter Lee ◽  
Abdel-Hakim Bouzid ◽  
James Huang
Keyword(s):  
Elevated Temperatures ◽  
Flow Behavior ◽  
Pressure Gauge ◽  
Pressure Rise ◽  
Operating Conditions ◽  
Test Method ◽  
Vacuum System ◽  
Molecular Flow ◽  
Vacuum Level ◽  
The Impact

Gasket performance for vacuum applications has not been well studied. Although a wealth of sealability data has been generated for pressurized systems, little is done with vacuum conditions. A new test method has been developed to study the sealing performance of gaskets for vacuum services. The tests were conducted on a standard ROTT test rig, where a vacuum chamber surrounding the gasket was created by an air pump and monitored by a pressure gauge capable of measuring pressures down to 0.1 Torr. Two levels of vacuum were used: 50 Torr and 3 Torr. Each tested gasket was compressed to various assembly stresses corresponding to the levels defined in the ROTT procedure. After the gasket was compressed to a desired stress and a target vacuum level was reached, the pumping stopped, and the leak rate was measured, using the pressure rise method. The similar leakage results with two very different vacuum levels confirm that sealing a vacuum system is simply to seal ∼1 bar of air. The air leakage was further compared with the helium leak rates obtained from the standard ROTT test with a pressure of 21 bar to determine the correlation between the two data sets. To better understand the effects of pressure and molecular size of a gas, two additional tests at 2 bar, with helium and with nitrogen, were performed. The comparison among all test data suggests that the gases at relatively low pressures follow a molecular flow behavior up to about 55 MPa of gasket stress on the tested material. As a result, a tightness curve that can be used to estimate the vacuum leakage has been established. For applications involving elevated temperatures, thermal behaviors of gaskets determined by other PVRC tests, such as the HOBT and ARLA, can be used to understand the impact of temperature on vacuum performance. A stress-tightness-temperature framework is proposed that can be used to estimate the tightness and leakage of the gasket at high temperatures. Knowing the air leak rates under different operating conditions, a gasket user will be able to determine the suitability of the gasket for a specific vacuum requirement as well as the optimal assembly stress to maintain the desired vacuum level.

Experimental Investigations of Particulate Size and Number Distribution in an Ethanol and Methanol Fueled HCCI Engine

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Rakesh Kumar Maurya ◽  
Avinash Kumar Agarwal
Keyword(s):  
Alternative Fuels ◽  
Fuel Injection ◽  
Operating Conditions ◽  
Experimental Investigations ◽  
Operating Parameters ◽  
Hcci Engine ◽  
Number Distribution ◽  
Auto Ignition ◽  
Size Number ◽  
Homogeneous Charge

Alcohols (ethanol and methanol) are being widely considered as alternative fuels for automotive applications. At the same time, homogeneous charge compression ignition (HCCI) engine has attracted global attention due to its potential of providing high engine efficiency and ultralow exhaust emissions. Environmental legislation is becoming increasingly stringent, sharply focusing on particulate matter (PM) emissions. Recent emission norms consider limiting PM number concentrations in addition to PM mass. Therefore, present study is conducted to experimentally investigate the effects of engine operating parameters on the PM size–number distribution in a HCCI engine fueled with gasoline, ethanol, and methanol. The experiments were conducted on a modified four-cylinder diesel engine, with one cylinder modified to operate in HCCI mode. Port fuel injection was used for preparing homogeneous charge in the HCCI cylinder. Intake air preheating was used to enable auto-ignition of fuel–air mixture. Engine exhaust particle sizer (EEPS) was used for measuring size–number distribution of soot particles emitted by the HCCI engine cylinder under varying engine operating conditions. Experiments were conducted at 1200 and 2400 rpm by varying intake air temperature and air–fuel ratio for gasoline, ethanol, and methanol. In this paper, the effect of engine operating parameters on PM size–number distribution, count mean diameter (CMD), and total PM numbers is investigated. The experimental data show that the PM number emissions from gasoline, ethanol, and methanol in HCCI cannot be neglected and particle numbers increase for relatively richer mixtures and higher intake air temperatures.

scholarly journals Experimental and Numerical Assessment of the Impact of an Integrated Active Pre-Swirl Generator on Turbocharger Compressor Performance and Operating Range

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3537
Author(s):  
Charles Stuart ◽  
Stephen Spence ◽  
Sönke Teichel ◽  
Andre Starke
Keyword(s):  
Mass Flow ◽  
Operating Conditions ◽  
Centrifugal Impeller ◽  
Boost Pressure ◽  
Flow Rates ◽  
Operating Range ◽  
Surge Margin ◽  
Mass Flow Rates ◽  
Low Mass ◽  
The Impact

The implementation of increasingly stringent emissions and efficiency targets has seen engine downsizing and other complementary technologies increase in prevalence throughout the automotive sector. In order to facilitate ongoing improvements associated with the use of these strategies, delivering enhancements to the performance and stability of the turbocharger compressor when operating at low mass flow rates is of paramount importance. In spite of this, a few concepts (either active or passive) targeting such aims have successfully transitioned into use in automotive turbochargers, due primarily to the requirement for a very wide compressor-operating range. In order to overcome the operational limitations associated with existing pre-swirl generation devices such as inlet guide vanes, this study developed a concept comprising of an electrically driven axial fan mounted upstream of a standard automotive turbocharger centrifugal compressor. Rather than targeting a direct contribution to compressor boost pressure, the fan was designed to act as a variable pre-swirl generation device capable of being operated completely independently of the centrifugal impeller. It was envisioned that this architecture would allow efficient generation of the large pre-swirl angles needed for compressor surge margin extension and efficiency enhancement at low mass flow rate-operating points, while also facilitating the delivery of zero pre-swirl at higher mass flow rates to ensure no detrimental impact on performance at the rated power point of the engine. Having progressed through 1-D and 3-D aerodynamic modelling phases to understand the potential of the system, detailed component design and hardware manufacture were completed to enable an extensive experimental test campaign to be conducted. The experimental results were scrutinized to validate the numerical findings and to test the surge margin extension potential of the device. Compressor efficiency improvements of up to 3.0% pts were witnessed at the target-operating conditions.

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