Elisa Toulson

A Review of Pre-Chamber Initiated Jet Ignition Combustion Systems

This paper reviews progress on turbulent jet ignition systems for otherwise standard spark ignition engines, with focus on small pre-chamber systems (<3% of clearance volume) with auxiliary prechamber fueling. The review covers a range of systems including early designs such as those by Gussak and Oppenheim and more recent designs proposed by GM, FEV, Bosch and MAHLE Powertrain. A major advantage of jet ignition systems is that they enable very fast burn rates due to the ignition system producing multiple, distributed ignition sites, which consume the main charge rapidly and with minimal combustion variability. The locally distributed ignition sites allow for increased levels of dilution (lean burn/EGR) when compared to conventional spark ignition combustion. Dilution levels are comparable to those reported in recent homogeneous charge compression ignition (HCCI) systems. In addition, jet ignition systems have the potential for combustion phasing control and hence speed/load range benefits when compared to HCCI, without the need for SI-HCCI combustion mode switching. The faster burn rates also allow for a base compression ratio increase (1-2 points) when compared to spark ignition and when combined with diluted mixture combustion, provide increased engine efficiency.

A Turbulent Jet Ignition Pre-Chamber Combustion System for Large Fuel Economy Improvements in a Modern Vehicle Powertrain

Turbulent Jet Ignition is an advanced pre-chamber initiated combustion system for an otherwise standard spark ignition engine found in current on-road vehicles. This next generation pre-chamber design overcomes previous packaging obstacles by simply replacing the spark plug in a modern four valve, pent roof spark ignition engine. Turbulent Jet Ignition enables very fast burn rates due to the ignition system producing multiple, distributed ignition sites, which consume the main charge rapidly and with minimal combustion variability. The fast burn rates allow for increased levels of dilution (lean burn and/or EGR) when compared to conventional spark ignition combustion, with dilution levels being comparable to other low temperature combustion technologies (homogeneous charge compression ignition HCCI) without the complex control drawbacks. This paper focuses on preliminary performance, efficiency, emissions and combustion effects of a Turbulent Jet Ignition system operated with commercially available fuels at the world wide mapping point of 1500 rev/min, 3.3 bar IMEPn ( 2.62 bar BMEP). Single cylinder experimental results highlight that the pre-chamber combustion system is capable of tolerating up to 54% mass fraction diluent while still maintaining adequate combustion stability. The high diluent fraction has enabled the prechamber combustion system to record an 18% improvement in fuel consumption when compared to conventional stoichiometric spark ignition. The efficiency improvements are due to a combination of combustion improvements, the near elimination of dissociation due to the low combustion temperatures and reduced engine throttling. Additionally, the low temperature combustion has resulted in single digit ppm engine out NOx emissions with controllable levels of HC and CO emissions.

Spark Ignition and Pre-Chamber Turbulent Jet Ignition Combustion Visualization

Natural gas is a promising alternative fuel as it is affordable, available worldwide, has high knock resistance and low carbon content. This study focuses on the combustion visualization of spark ignition combustion in an optical single cylinder engine using natural gas at several air to fuel ratios and speed‐load operating points. In addition, Turbulent Jet Ignition optical images are compared to the baseline spark ignition images at the world‐wide mapping point (1500 rev/min, 3.3 bar IMEPn) in order to provide insight into the relatively unknown phenomenon of Turbulent Jet Ignition combustion. Turbulent Jet Ignition is an advanced spark initiated pre‐chamber combustion system for otherwise standard spark ignition engines found in current passenger vehicles. This next generation pre‐chamber design simply replaces the spark plug in a conventional spark ignition engine. Turbulent Jet Ignition enables very fast burn rates due to the ignition system producing multiple, widely distributed ignition sites, which consume the main charge rapidly. This high energy ignition results from the partially combusted (reacting) pre‐chamber products initiating combustion in the main chamber. The distributed ignition sites enable relatively small flame travel distances enabling short combustion durations and high burn rates. Multiple benefits include extending the knock limit and initiating combustion in very dilute mixtures (excess air and/or EGR), with dilution levels being comparable to other low temperature combustion technologies (HCCI), without the complex control drawbacks.

A Study of an Energetically Enhanced Plasma Ignition System for Internal Combustion Engines

The effects of a plasma enhanced ignition system on the performance of a small, single cylinder, and four-stroke gasoline engine are examined. Dynamometer testing of the 33.5- cm3 engine at various operating speeds was performed with both the engines stock coil ignition system and a radio frequency (RF) plasma ignition system. The RF system is designed to provide a quasi-nonequilibrium plasma discharge that features a high voltage pulsar that provides 400 mJ of energy for each discharge and voltages of up to 30 kV. Tests show improvement of the engines combustion stability at all operating conditions and the extension of the engines lean flammability limit with the RF system. Particular attention is given to the improvements that the RF system provides while burning lean air fuel mixtures. In addition, gas analysis of the 33.5- cm3 engines exhaust and high speed images of the RF system taken in a separate 0.4-L optical engine are also presented.

A Computational Study on the Effect of the Orifice Size on the Performance of a Turbulent Jet Ignition System

Fully three-dimensional computational fluid dynamic simulations with detailed combustion chemistry of a turbulent jet ignition system installed in a rapid compression machine are presented. The turbulent jet ignition system is a prechamber-initiated combustion system intended to allow lean-burn combustion in spark ignition internal-combustion engines. In the presented configuration, the turbulent jet ignition prechamber has a volume that is 2% of the volume of the main combustion chamber in the rapid compression machine and is separated from the main chamber by a nozzle containing a single orifice. Four simulations with orifice diameters of 1.0 mm, 1.5 mm, 2.0 mm, and 3.0 mm respectively are presented in order to demonstrate the effect of the orifice diameter on the combustion behavior of the turbulent jet ignition process. Data generated by the simulations is shown including combustion chamber pressures, temperature fields, jet velocities and mass fraction burn durations. From the combustion pressure trace, the jet velocity, and other field data, five distinct phases of the turbulent jet ignition process are identified. These phases are called the compression phase, the prechamber combustion initiation phase, the cold jet phase, the hot jet phase, and the flow reversal phase. The four simulations show that the orifice diameter of 1.5 mm provides the fastest ignition and the fastest overall combustion as reflected in the 0–10% and 10–90% mass fraction burn duration data generated. Meanwhile, the simulation for the orifice diameter of 1.0 mm produces the highest jet velocity and has the shortest delay between the spark and the exit of a jet of hot gases into the main chamber but produces a slower burn duration than the simulation for the larger orifice diameter of 1.5 mm. The simulations for orifice diameters of 2.0 mm and 3.0 mm demonstrate that the combustion speed is reduced as the orifice diameter increases above 1.5 mm. Finally, a discussion is given which examines the implications that the results generated have in regard to implementation of the turbulent jet ignition system in an internal-combustion engine.

Compression ratio effects on performance, efficiency, emissions and combustion in a carbureted and PFI small engine

This paper compares the performance, efficiency, emissions and combustion parameters of a prototype two cylinder 430 cm 3 engine which has been tested in a variety of normally aspirated (NA) modes with compression ratio (CR) variations. Experiments were completed using 98-RON pump gasoline with modes defined by alterations to the induction system, which included carburetion and port fuel injection (PFI). The results from this paper provide some insight into the CR effects for small NA spark ignition (SI) engines. This information provides future direction for the development of smaller engines as engine downsizing grows in popularity due to rising oil prices and recent carbon dioxide (CO2) emission regulations. Results are displayed in the engine speed, manifold absolute pressure (MAP) and CR domains, with engine speeds exceeding 10000 rev/min and CRs ranging from 9 to 13. Combustion analysis is also included, allowing mass fraction burn (MFB) comparison. Experimental results showed minimum brake specific fuel consumption (BSFC) or maximum brake thermal efficiency (ηTH) values in the order of 220 g/kWh or 37% could be achieved. A maximum brake mean effective pressure (BMEP) of 13 bar was also recorded at 8000 rev/min.

The feasibility of downsizing a 1.25 liter normally aspirated engine to a 0.43 liter highly turbocharged engine

In this paper, performance, efficiency and emission experimental results are presented from a prototype 434 cm, highly turbocharged (TC), two cylinder engine with brake power limited to approximately 60 kW. These results are compared to current small engines found in today’s automobile marketplace. A normally aspirated (NA) 1.25 liter, four cylinder, modern production engine with similar brake power output is used for comparison. Results illustrate the potential for downsized engines to significantly reduce fuel consumption while still maintaining engine performance. This has advantages in reducing vehicle running costs together with meeting tighter carbon dioxide (CO2) emission standards. Experimental results highlight the performance potential of smaller engines with intake boosting. This is demonstrated with the test engine achieving 25 bar brake mean effective pressure (BMEP). Results are presented across varying parameter domains, including engine speed, compression ratio (CR), manifold absolute pressure (MAP) and lambda (λ). Engine operating limits are also outlined, with spark knock highlighted as the major limitation in extending the operating limits for this downsized engine.

Combustion System Development and Analysis of a Carbureted and PFI Normally Aspirated Small Engine

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A control-oriented model of turbulent jet ignition combustion in a rapid compression machine

Turbulent jet ignition combustion is a promising concept for achieving high thermal efficiency and low NOx (nitrogen oxides) emissions. A control-oriented turbulent jet ignition combustion model with satisfactory accuracy and low computational effort is usually a necessity for optimizing the turbulent jet ignition combustion system and developing the associated model-based turbulent jet ignition control strategies. This article presents a control-oriented turbulent jet ignition combustion model developed for a rapid compression machine configured for turbulent jet ignition combustion. A one-zone gas exchange model is developed to simulate the gas exchange process in both pre- and main-combustion chambers. The combustion process is modeled by a two-zone combustion model, where the ratio of the burned and unburned gases flowing between the two combustion chambers is variable. To simulate the influence of the turbulent jets on the rate of combustion in the main-combustion chamber, a new parameter-varying Wiebe function is proposed and used for the mass fraction burned calculation in the main-combustion chamber. The developed model is calibrated using the least-squares fitting and optimization procedures. Experimental data sets with different air-to-fuel ratios in both combustion chambers and different pre-combustion chamber orifice areas are used to calibrate and validate the model. The simulation results show good agreement with the experimental data for all the experimental data sets. This indicates that the developed combustion model is accurate for developing and validating turbulent jet ignition combustion control strategies. Future work will extend the rapid compression machine combustion model to engine applications.

Autoignition Behavior of Petroleum-Based and Hydroprocessed Renewable Jet Fuel Blends in a Rapid Compression Machine

A rapid compression machine (RCM) is used to study the autoignition characteristics of JP-8 and JP-5 blended in 50-50 mixtures by volume with their respective camelina-derived hydroprocessed renewable jet (HRJ) fuel at low temperature conditions. The tests employ the direct test chamber (DTC) charge preparation method which allows for high reproducibility of measurements. Ignition delay measurements are compared between the conventional military jet fuels, HRJ fuels, and the 50-50 blends. Measurements are made at compressed pressures of 5, 10, and 20 bar at an equivalence ratio of 1.0 and compressed temperatures between 625 K and 710 K. Additional ignition delay measurements are reported at reduced equivalence ratios of 0.5 and 0.25 at a compressed pressure of 20 bar and temperatures between 635 K and 720 K.