Knock In Various Combustion Modes in a Gasoline-Fueled Automotive Engine

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Jiri Vavra ◽  
Stanislav V. Bohac ◽  
Laura Manofsky ◽  
George Lavoie ◽  
Dennis Assanis
Keyword(s):  
Maximum Load ◽  
Simultaneous Occurrence ◽  
Compression Ignition ◽  
Automotive Engine ◽  
Hcci Combustion ◽  
Combustion Modes ◽  
Spark Plug ◽  
Load Increase ◽  
Research Grade ◽  
Stability Limits

Homogeneous charge compression ignition (HCCI) offers great potential for improved fuel economy and dramatically reduced NOx emissions, compared to typical spark ignition (SI) combustion. However, the benefits of HCCI are limited to low and medium loads by the simultaneous occurrence of combustion instability and knock at a maximum load that is too low for conventional SI combustion. To provide smooth operation in the intermediate range between HCCI and SI requires alternative combustion strategies. One such strategy is spark-assisted compression ignition (SACI), which uses a spark plug to initiate a flame that consumes a portion of the mixture, followed by autoignition of the remaining charge. This moderates the rapid heat release and allows higher loads to be achieved without exceeding knock and stability limits. In a recent study, we have explored this region and have found that spark assist at first dramatically reduces knock as load is raised above the HCCI limit; however, with further load increase, knock returns but in a form that resembles spark ignited knock rather than the HCCI knock. This study investigates in detail the knocking conditions observed in that work. The objectives of this study are twofold: first, to explore the differences between the two forms of knock and second, to apply and compare a number of commonly used metrics for knock and noise over the range of HCCI, SACI, and SI combustion. Experimental data were acquired on a single-cylinder DI research engine equipped with a fully flexible valve actuation (FFVA) system and fueled by research-grade gasoline. Cycle to cycle results based on filtered pressure traces are shown and compared with a number of knock measures including a widely used correlation for ringing intensity for HCCI combustion. Although based on a limited set of data, the results identify important qualitative features of the two forms of knock and point out significant differences among the knock metrics. The results suggest that further investigations are needed to fully understand both the knocking phenomenon and how best to quantify it.

Knock in Various Combustion Modes in a Gasoline-Fueled Automotive Engine

2011 ◽  
Author(s):  
Jiri Vavra ◽  
Stanislav V. Bohac ◽  
Laura Manofsky ◽  
George Lavoie ◽  
Dennis N. Assanis
Keyword(s):  
Maximum Load ◽  
Simultaneous Occurrence ◽  
Compression Ignition ◽  
Automotive Engine ◽  
Hcci Combustion ◽  
Combustion Modes ◽  
Spark Plug ◽  
Load Increase ◽  
Research Grade ◽  
Stability Limits

Homogeneous charge compression ignition (HCCI) offers great potential for improved fuel economy and dramatically reduced NOx emissions, compared to typical spark ignition (SI) combustion. However the benefits of HCCI are limited to low and medium loads by the simultaneous occurrence of combustion instability and knock at a maximum load that is too low for conventional SI combustion. To provide smooth operation in the intermediate range between HCCI and SI requires alternative combustion strategies. One such strategy is spark-assisted compression ignition (SACI) which uses a spark plug to initiate a flame which consumes a portion of the mixture, followed by autoignition of the remaining charge. This moderates the rapid heat release and allows higher loads to be achieved without exceeding knock and stability limits. In a recent study we have explored this region and have found that spark assist at first dramatically reduces knock as load is raised above the HCCI limit; however with further load increase, knock returns, but in a form which resembles spark ignited knock rather than the HCCI knock. This study investigates in detail the knocking conditions observed in that work. The objectives of this study are twofold: first, to explore the differences between the two forms of knock; and second, to apply and compare a number of commonly used metrics for knock and noise over the range of HCCI, SACI and SI combustion. Experimental data were acquired on a single-cylinder DI research engine equipped with a fully flexible valve actuation (FFVA) system and fueled by research-grade gasoline. Cycle to cycle results based on filtered pressure traces are shown and compared with a number of knock measures including a widely used correlation for ringing intensity for HCCI combustion. Although based on a limited set of data, the results identify important qualitative features of the two forms of knock and point out significant differences among the knock metrics. The results suggest that further investigations are needed to fully understand both the knocking phenomenon and how best to quantify it.

Mapping the combustion modes of a dual-fuel compression ignition engine

2021 ◽  
pp. 146808742110183
Author(s):  
Jonathan Martin ◽  
André Boehman
Keyword(s):  
Direct Injection ◽  
Fuel Combustion ◽  
Dual Fuel ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Combustion Modes ◽  
Si Engines ◽  
Dual Fuel Combustion ◽  
Soot Emissions ◽  
Ci Engines

Compression-ignition (CI) engines can produce higher thermal efficiency (TE) and thus lower carbon dioxide (CO2) emissions than spark-ignition (SI) engines. Unfortunately, the overall fuel economy of CI engine vehicles is limited by their emissions of nitrogen oxides (NOx) and soot, which must be mitigated with costly, resource- and energy-intensive aftertreatment. NOx and soot could also be mitigated by adding premixed gasoline to complement the conventional, non-premixed direct injection (DI) of diesel fuel in CI engines. Several such “dual-fuel” combustion modes have been introduced in recent years, but these modes are usually studied individually at discrete conditions. This paper introduces a mapping system for dual-fuel CI modes that links together several previously studied modes across a continuous two-dimensional diagram. This system includes the conventional diesel combustion (CDC) and conventional dual-fuel (CDF) modes; the well-explored advanced combustion modes of HCCI, RCCI, PCCI, and PPCI; and a previously discovered but relatively unexplored combustion mode that is herein titled “Piston-split Dual-Fuel Combustion” or PDFC. Tests show that dual-fuel CI engines can simultaneously increase TE and lower NOx and/or soot emissions at high loads through the use of Partial HCCI (PHCCI). At low loads, PHCCI is not possible, but either PDFC or RCCI can be used to further improve NOx and/or soot emissions, albeit at slightly lower TE. These results lead to a “partial dual-fuel” multi-mode strategy of PHCCI at high loads and CDC at low loads, linked together by PDFC. Drive cycle simulations show that this strategy, when tuned to balance NOx and soot reductions, can reduce engine-out CO2 emissions by about 1% while reducing NOx and soot by about 20% each with respect to CDC. This increases emissions of unburnt hydrocarbons (UHC), still in a treatable range (2.0 g/kWh) but five times as high as CDC, requiring changes in aftertreatment strategy.

TWC-SCR Aftertreatment System Evaluation for a Lean Burn Gasoline Engine Operating in HCCI, SACI, and SI Combustion Modes

2016 ◽  
Author(s):  
Jordan Easter ◽  
Stanislav V. Bohac
Keyword(s):  
Conversion Efficiency ◽  
Gasoline Engine ◽  
Fuel Efficiency ◽  
Compression Ignition ◽  
Scr Catalyst ◽  
Advanced Combustion ◽  
Nox Conversion ◽  
Combustion Modes ◽  
Scr System ◽  
Nox Conversion Efficiency

Low temperature and dilute Homogenous Charge Compression Ignition (HCCI) and Spark Assisted Compression Ignition (SACI) can improve fuel economy and reduce engine-out NOx emissions to very low values, often less than 30 ppm. However, these combustion modes are unable to achieve stringent future regulations such as SULEV 30 without the use of lean aftertreatment. Though active selective catalytic reduction (SCR) with urea injection and lean NOx traps (LNT) have been investigated as options for lean gasoline engines, a passive TWC-SCR system is investigated in this work because it avoids the urea storage and dosing hardware of a urea SCR system, and the high precious metal cost of an LNT. The TWC-SCR concept uses periodic rich operation to produce NH3 over a TWC to be stored on an SCR catalyst for subsequent NOx conversion during lean operation. In this work a laboratory study was performed with a modified 2.0 L gasoline engine that was cycled between lean HCCI and rich SACI operation, or between lean and rich SI (spark ignited) combustion, to evaluate NOx conversion and reduced fuel consumption. Different lambda values during rich operation and different times held in rich operation were investigated. Results are compared to a baseline case in which the engine is always operated at stoichiometric conditions. SCR system simulations are also presented that compare system performance for different levels of stored NH3. With the configuration used in this study, lean/rich HCCI/SACI operation showed a maximum NOx conversion efficiency of 10%, while lean/rich SI operation showed a maximum NOx conversion efficiency of 60%. However, if the low conversion efficiency of lean/rich HCCI/SACI operation could be improved through higher brick temperatures or additional SCR bricks, simulation results indicate TWC-SCR aftertreatment has the potential to provide near-zero SCR-out NOx concentration and increased system fuel efficiency. In these simulations, fuel efficiency improvement relative to stoichiometric SI were 7 to15% for lean/rich HCCI/SACI with zero tailpipe NOx and −1 to 5% for lean/rich SI with zero tailpipe NOx emissions. Although previous work indicated increased time for NH3 to start forming over the TWC during rich operation, less NH3 production over the TWC per fuel amount, and increased NH3 slip over the SCR catalyst for advanced combustion systems, if NOx conversion efficiency could be enhanced, improvements in fuel economy and low engine-out NOx from advanced combustion modes would more than make up for these disadvantages.

Residual-effected homogeneous charge compression ignition at a low compression ratio using exhaust reinduction

2003 ◽  
Vol 4 (3) ◽  
pp. 163-177 ◽  
Author(s):  
P. A. Caton ◽  
A. J. Simon ◽  
J. C. Gerdes ◽  
C. F. Edwards
Keyword(s):  
Compression Ratio ◽  
Equivalence Ratio ◽  
Homogeneous Charge Compression Ignition ◽  
Compression Ignition ◽  
Single Digit ◽  
Hcci Combustion ◽  
Actuation System ◽  
Order Of Magnitude ◽  
No Emissions ◽  
Homogeneous Charge

Studies have been conducted to assess the performance of homogeneous charge compression ignition (HCCI) combustion initiated by exhaust reinduction from the previous engine cycle. Reinduction is achieved using a fully flexible electrohydraulic variable-valve actuation system. In this way, HCCI is implemented at low compression ratio without throttling the intake or exhaust, and without preheating the intake charge. By using late exhaust valve closing and late intake valve opening strategies, steady HCCI combustion was achieved over a range of engine conditions. By varying the timing of both valve events, control can be exerted over both work output (load) and combustion phasing. In comparison with throttled spark ignition (SI) operation on the same engine, HCCI achieved 25–55 per cent of the peak SI indicated work, and did so at uniformly higher thermal efficiency. This was accompanied by a two order of magnitude reduction in NO emissions. In fact, single-digit (ppm) NO emissions were realized under many load conditions. In contrast, hydrocarbon emissions proved to be significantly higher in HCCI combustion under almost all conditions. Varying the equivalence ratio showed a wider equivalence ratio tolerance at low loads for HCCI.

Study of High Load Operation Limit Expansion for Gasoline Compression Ignition Engines

2006 ◽  
Vol 128 (2) ◽  
pp. 377-387 ◽  
Author(s):  
Koudai Yoshizawa ◽  
Atsushi Teraji ◽  
Hiroshi Miyakubo ◽  
Koichi Yamaguchi ◽  
Tomonori Urushihara
Keyword(s):  
Fuel Injection ◽  
Control Method ◽  
Combustion Process ◽  
High Load ◽  
Compression Ignition ◽  
Ignition Timing ◽  
Timing Control ◽  
Load Range ◽  
Compression Ignition Engines ◽  
Spark Plug

In this research, combustion characteristics of gasoline compression ignition engines have been analyzed numerically and experimentally with the aim of expanding the high load operation limit. The mechanism limiting high load operation under homogeneous charge compression ignition (HCCI) combustion was clarified. It was confirmed that retarding the combustion timing from top dead center (TDC) is an effective way to prevent knocking. However, with retarded combustion, combustion timing is substantially influenced by cycle-to-cycle variation of in-cylinder conditions. Therefore, an ignition timing control method is required to achieve stable retarded combustion. Using numerical analysis, it was found that ignition timing control could be achieved by creating a fuel-rich zone at the center of the cylinder. The fuel-rich zone works as an ignition source to ignite the surrounding fuel-lean zone. In this way, combustion consists of two separate auto-ignitions and is thus called two-step combustion. In the simulation, the high load operation limit was expanded using two-step combustion. An engine system identical to a direct-injection gasoline (DIG) engine was then used to validate two-step combustion experimentally. An air-fuel distribution was created by splitting fuel injection into first and second injections. The spark plug was used to ignite the first combustion. This combustion process might better be called spark-ignited compression ignition combustion (SI-CI combustion). Using the spark plug, stable two-step combustion was achieved, thereby validating a means of expanding the operation limit of gasoline compression ignition engines toward a higher load range.

Characterizing the cyclic variability of ignition timing in a homogeneous charge compression ignition engine fuelled with n-heptane/iso-octane blend fuels

2008 ◽  
Vol 9 (5) ◽  
pp. 361-397 ◽  
Author(s):  
M Shahbakhti ◽  
C R Koch
Keyword(s):  
Equivalence Ratio ◽  
Homogeneous Charge Compression Ignition ◽  
Coolant Temperature ◽  
Cyclic Variation ◽  
Compression Ignition ◽  
Ignition Timing ◽  
Compression Ignition Engine ◽  
Hcci Combustion ◽  
Cyclic Variations ◽  
Homogeneous Charge

The cyclic variations of homogeneous charge compression ignition (HCCI) ignition timing is studied for a range of charge properties by varying the equivalence ratio, intake temperature, intake pressure, exhaust gas recirculation (EGR) rate, engine speed, and coolant temperature. Characterization of cyclic variations of ignition timing in HCCI at over 430 operating points on two single-cylinder engines for five different blends of primary reference fuel (PRF), (iso-octane and n-heptane) is performed. Three distinct patterns of cyclic variation for the start of combustion (SOC), combustion peak pressure ( Pmax), and indicated mean effective pressure (i.m.e.p.) are observed. These patterns are normal cyclic variations, periodic cyclic variations, and cyclic variations with weak/misfired ignitions. Results also show that the position of SOC plays an important role in cyclic variations of HCCI combustion with less variation observed when SOC occurs immediately after top dead centre (TDC). Higher levels of cyclic variations are observed in the main (second) stage of HCCI combustion compared with that of the first stage for the PRF fuels studied. The sensitivity of SOC to different charge properties varies. Cyclic variation of SOC increases with an increase in the EGR rate, but it decreases with an increase in equivalence ratio, intake temperature, and coolant temperature.

Active valvetrain for homogeneous charge compression ignition

2005 ◽  
Vol 6 (4) ◽  
pp. 377-397 ◽  
Author(s):  
N Milovanovic ◽  
J G W Turner ◽  
S A Kenchington ◽  
G Pitcher ◽  
D W Blundell
Keyword(s):  
Homogeneous Charge Compression Ignition ◽  
Cold Start ◽  
Smooth Transition ◽  
Engine Management System ◽  
Compression Ignition ◽  
Load Range ◽  
Hcci Combustion ◽  
Particulate Matter Emissions ◽  
Mode Transitions ◽  
Homogeneous Charge

Homogeneous charge compression ignition (HCCI), also known as controlled autoignition (CAI) or the premixed charge compression ignition (PCCI) engine concept, has the potential to be highly efficient and to produce low NOx, carbon dioxide, and particulate matter emissions. However, it experiences problems with cold start in a gasoline HCCI engine, running at idle and at high loads, which, together with controlling the combustion over the entire speed/load range, limits its practical application. A way to overcome these problems is to operate the engine in ‘hybrid mode’, where the engine operates in HCCI mode at low, medium, and cruising loads and can switch to or from spark ignition (SI) or diesel (CI) mode for a cold start, idle, and higher loads. Such an engine will have frequent changes in engine load and speeds and therefore frequent transitions between HCCI and SI combustion modes. The valvetrain and engine management system (EMS) have to provide a successful control of HCCI mode and a fast and smooth transition keeping all relevant engine parameters within an acceptable range. Consequently, this leads to high demands on the valvetrain and therefore a need for a very high degree of flexibility. The aim of this paper is to present the potential of a fully variable valvetrain (FVVT) system, the Lotus active valvetrain (AVT™), for controlling HCCI combustion and enabling fast and smooth mode transitions in a HCCI/SI engine fuelled with commercially available gasoline (95 RON) and in a HCCI/DI engine fuelled with diesel (50 CN) fuel.

Modeling advanced combustion modes in compression ignition engines with tabulated kinetics

2019 ◽  
Vol 247 ◽  
pp. 537-548 ◽  
Author(s):  
T. Lucchini ◽  
A. Della Torre ◽  
G. D’Errico ◽  
A. Onorati
Keyword(s):  
Compression Ignition ◽  
Compression Ignition Engines ◽  
Advanced Combustion ◽  
Combustion Modes
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