Search Results

A novel continuous inductive discharge ignition system has been developed that allows for variable duration ignition events in SI engines. The system uses a dual-coil design, where two coils are connected by a diode, combined with the multi-striking coil concept, to generate a continuous current flow through the spark plug. The current level and duration can be regulated by controlling the number of re-strikes that each coil performs or the energy density the primary coils are charged to. Compared to other extended duration systems, this system allows for fairly high current levels during the entire discharge event while avoiding the extremely high discharge levels associated with other, shorter duration, high energy ignition systems (e.g. the plasma jet [ 1 , 2 ], railplug [ 3 ] or laser ignition systems [ 4 , 5 , 6 , 7 , 8 ].

A 13 L HD diesel engine was converted to run as a flame propagation engine using the HEDGE™ Dual-Fuel concept. This concept consists of pre-mixed gasoline ignited by a small amount of diesel fuel - i.e., a diesel micropilot. Due to the large bore size and relatively high compression ratio for a pre-mixed combustion engine, high levels of cooled EGR were used to suppress knock and reduce the engine-out emissions of the oxides of nitrogen and particulates. Previous work had indicated that the boosting of high dilution engines challenges most modern turbocharging systems, so phase I of the project consisted of extensive simulation efforts to identify an EGR configuration that would allow for high levels of EGR flow along the lug curve while minimizing pumping losses and combustion instabilities from excessive backpressure. A potential solution that provided adequate BTE potential was consisted of dual loop EGR systems to simultaneously flow high pressure and low pressure loop EGR.

SwRI has developed the DCO® ignition system, a unique continuous discharge system that allows for variable duration/energy events in SI engines. The system uses two coils connected by a diode and a multi-striking controller to generate a continuous current flow through the spark plug of variable duration. A previous publication demonstrated the ability of the DCO system to improve EGR tolerance using low energy coils. In this publication, the work is extended to high current (≻ 300 mA/high energy (≻ 200 mJ) coils and compared to several advanced ignition systems. The results from a 4-cylinder, MPI application demonstrate that the higher current/higher energy coils offer an improvement over the lower energy coils. The engine was tested at a variety of speed and load conditions operating at stoichiometric air-fuel ratios with gasoline and EGR dilution.

A unique single cylinder engine was used to assess engine performance and combustion characteristics at three different strokes, with all other variables held constant. The engine utilized a production four-valve, pentroof cylinder head with an 86mm bore. The stock piston was used, and a variable deck height design allowed three crankshafts with strokes of 86, 98, and 115mm to be tested. The compression ratio was also held constant. The engine was run with a controlled boost-to-backpressure ratio to simulate turbocharged operation, and the valve events were optimized for each operating condition using intake and exhaust cam phasers. EGR rates were swept from zero to twenty percent under low and high speed conditions, at MBT and maximum retard ignition timings. The increased stroke engines demonstrated efficiency gains under all operating conditions, as well as measurably reduced 10-to-90 percent burn durations.

A series of ignition systems were evaluated for their suitability for high-EGR SI engine applications. Testing was performed in a constant-volume combustion chamber and in a single-cylinder research engine, with EGR rates of up to 40% evaluated. All of the evaluated systems were able to initiate combustion at a simulated 20% EGR level, but not all of the resulting combustion rates were adequate for stable engine operation. High energy spark discharge systems were better, and could ignite a flame at up to 40% simulated EGR, though again the combustion rates were slow relative to that required for stable engine performance. The most effective systems for stable combustion at high EGR rates were systems which created a large effective flame kernel and/or a long kernel lifetime, such as a torch-style prechamber spark plug or a corona discharge igniter.

A turbocharged 2.0 L PFI engine was modified to operate in a low-pressure loop and Dedicated EGR (D-EGR®) engine configuration. Both engine architectures were operated with a low and high octane gasoline as well as three ethanol blends. The core of this study focused on examining combustion differences at part and high loads between the selected fuels and also the different engine configurations. Specifically, the impact of the fuels on combustion stability, burn rates, knock mitigation, required ignition energy, and efficiency were evaluated. The results showed that the knock resistance generally followed the octane rating of the fuel. At part loads, the burn rates, combustion stability, and EGR tolerance was marginally improved with the high ethanol blends. When combustion was not knock or stability limited, the efficiency differences between the fuels were negligible. The D-EGR engine was much less sensitive to fuel changes in terms of burn rates than the LPL EGR setup.

Dedicated EGR (D-EGR) is an EGR strategy that uses in-cylinder reformation to improve fuel economy and reduce emissions. The entire exhaust of a sub-group of power cylinders (dedicated cylinders) is routed directly into the intake. These cylinders are run fuel-rich, producing H2 and CO (reformate), with the potential to improve combustion stability, knock tolerance and burn duration. A 2.0 L turbocharged D-EGR engine was packaged into a 2012 Buick Regal and evaluated on drive cycle performance. City and highway fuel consumption were reduced by 13% and 9%, respectively. NOx + NMOG were 31 mg/mile, well below the Tier 2 Bin 5 limit and just outside the Tier 3 Bin 30 limit (30 mg/mile).

Downsizing is an important concept to reduce fuel consumption as well as emissions of spark ignition engines. Engine displacement is reduced in order to shift operating points from lower part load into regions of the operating map with higher efficiency and thus lower specific fuel consumption [ 1 ]. Since maximum power in full load operation decreases due to the reduction of displacement, engines are boosted (turbocharging or supercharging), which leads to a higher specific loading of the engines. Hence, a new combustion phenomenon has been observed at high loads and low engine speed and is referred to as Low-Speed Pre-Ignition or LSPI. In cycles with LSPI, the air/fuel mixture is ignited prior to the spark which results in the initial flame propagation quickly transforming into heavy engine knock. Very high pressure rise rates and peak cylinder pressures could exceed design pressure limits, which in turn could lead to degradation of the engine.

The mixture preparation process was investigated in a direct-injected, 4-valve, SI engine under motored conditions. The engine had a transparent cylinder liner that allowed the fuel spray to be imaged using laser sheet Mie scattering. A fiber optic probe was used to measure the vapor phase fuel concentration history at the spark plug location between the two intake valves. The fuel injector was located on the cylinder axis. Two flow fields were examined; the stock configuration (tumble index 1.4) and a high tumble (tumble index 3.4) case created using shrouded intake valves. The fuel spray was visualized with the engine motored at 750 and 1500 RPM. Start of injection timings of 90°, 180° and 270° after TDC of intake were examined. The imaging showed that the fuel jet is greatly distorted for the high tumble condition, particularly at higher engine speeds. The tumble was large enough to cause significant cylinder wall wetting under the exhaust valves for some conditions.

Low-speed pre-ignition (LSPI) is a well-studied phenomenon in boosted, spark ignition engines. The impact of lubricant formulation has received a lot of attention in recent years, yet the impact of engine hardware and engine wear on LSPI is still not fully understood. This paper addresses some of these questions using results from multiple installations of the GM 2.0 L LHU engine platform. In the first part of the study, the effect of engine life on LSPI activity was observed, and it was found that engines were susceptible to variations in LSPI activity during the initial LSPI tests with the activity eventually reaching a “stabilized” level. It was further observed that the LSPI activity generally continued to decline at a steady rate as the engine aged. For engines used in LSPI testing, the life of the engine is often limited as LSPI activity decays with age.

The use of cooled EGR in gasoline engines improves the fuel efficiency of the engine through a variety of mechanisms, including improving the charge properties (e.g. the ratio of specific heats), reducing knock and enabling higher compression ratio operation and, at part loads conditions in particular, reducing pumping work. One of the limiting factors on the level of improvement from cooled EGR is the ability of the ignition system to ignite a dilute mixture and maintain engine stability. Previous work from SwRI has shown that, by increasing the ignition duration and using a continuous discharge ignition system, an improved ignition system can substantially increase the EGR tolerance of an engine [1, 2]. This improvement comes at a cost, however, of increased ignition system energy requirements and a potential decrease in spark plug durability. This work examines the impact of engine operating parameters on the ignition energy requirements under high dilution operation.

Dual fuel engines have shown significant potential as high efficiency powerplants. In one example, SwRI® has run a high EGR, dual-fuel engine using gasoline as the main fuel and diesel as the ignition source, achieving high thermal efficiencies with near zero NOx and smoke emissions. However, assuming a tank size that could be reasonably packaged, the diesel fuel tank would need to be refilled often due to the relatively high fraction of diesel required. To reduce the refill interval, SwRI investigated various alternative fluids as potential ignition sources. The fluids included: Ultra Low Sulfur Diesel (ULSD), Biodiesel, NORPAR (a commercially available mixture of normal paraffins: n-pentadecane (normal C15H32), and n-hexadecane (normal C16H34)) and ashless lubrication oil. Lubrication oil was considered due to its high cetane number (CN) and high viscosity, hence high ignitability.

The ongoing pursuit of improved engine efficiency and emissions is driving gasoline low-pressure loop EGR systems into production around the globe. The Dedicated EGR (D-EGR®) engine was developed to minimize some of the challenges of cooled EGR while maintaining its advantages. The D-EGR engine is a high efficiency, low emissions internal combustion engine for automotive and off-highway applications. The core of the engine development focused on a unique concept that combines the efficiency improvements associated with recirculated exhaust gas and the efficiency improvements associated with fuel reformation. To outline the differences of the new engine concept with a conventional LPL EGR setup, a turbocharged 2.0 L PFI engine was modified to operate in both modes. The second part of the cooled EGR engine concept comparison investigates efficiency, knock resistance, combustion stability, and maximum load potential at high load conditions.

The performance and efficiency of spark ignited gasoline engines is often limited by end-gas knock. In particular, when operating the engine at high loads, combustion phasing is retarded to prevent knock, resulting in a significant reduction of engine efficiency. Since the invention of the spark ignition (SI) engine, much work has been devoted to improve and regulate fuel characteristics, such as octane number, to suppress engine knock. The auto-ignition tendency of the engine lubricant however, as described by cetane number (CN), has received little attention, as it has been assumed that engine lubricant effects on knock are insignificant, primarily due to low levels of average oil consumption. However, with modern SI engines being developed to operate at higher loads and closer to knock limits, the reactivity of engine lubricants can impact the knock behavior.

The primary focus of this investigation was to determine the hydrogen reformation, efficiency and knock mitigation benefits of methanol-fueled Dedicated EGR (D-EGR®) operation, when compared to other EGR types. A 2.0 L turbocharged port fuel injected engine was operated with internal EGR, high-pressure loop (HPL) EGR and D-EGR configurations. The internal, HPL-EGR, and D-EGR configurations were operated on neat methanol to demonstrate the relative benefit of D-EGR over other EGR types. The D-EGR configuration was also tested on high octane gasoline to highlight the differences to methanol. An additional sub-task of the work was to investigate the combustion response of these configurations. Methanol did not increase its H2 yield for a given D-EGR cylinder equivalence ratio, even though the H:C ratio of methanol is over twice typical gasoline.

High dilution engines have been shown to have a significant fuel economy improvement over their non-dilute counterparts. Much of this improvement comes through an increase in compression ratio enabled by the high knock resistance from high dilution. Unfortunately, the same reduction in reactivity that leads to the knock reduction also reduces flame speed, leading to the engine becoming unstable at high dilution rates. Advanced ignition systems have been shown to improve engine stability, but their impact is limited to the area at, or very near, the spark plug. To further improve the dilute combustion, a system in which a microwave field is established in the combustion chamber is proposed. This standing electric field has been shown, in other applications, to improve dilution tolerance and increase the burning velocity.

In light of the increasingly stringent efficiency and emissions requirements, several new engine technologies are currently under investigation. One of these new concepts is the Dedicated EGR (D-EGR®) engine. The concept utilizes fuel reforming and high levels of recirculated exhaust gas (EGR) to achieve very high levels of thermal efficiency. While the positive impact of reformate, in particular hydrogen, on gasoline engine performance has been widely documented, the on-board reforming process and / or storage of H2 remains challenging. The Water-Gas-Shift (WGS) reaction is well known and has been used successfully for many years in the industry to produce hydrogen from the reactants water vapor and carbon monoxide. For this study, prototype WGS catalysts were installed in the exhaust tract of the dedicated cylinder of a turbocharged 2.0 L in-line four cylinder MPI engine. The potential of increased H2 production in a D-EGR engine was evaluated through the use of these catalysts.

The spark ignition (SI) engine has been known to exhibit several different abnormal combustion phenomena, such as knock or pre-ignition, which have been addressed with improved engine design or control schemes. However, in highly boosted SI engines - where the engine displacement is reduced and turbocharging is employed to increase specific power - a new combustion phenomenon, described as Low-Speed Pre-Ignition (LSPI), has been exhibited. LSPI is characterized as a pre-ignition event typically followed by heavy knock, which has the potential to cause degradation of the engine. However, because LSPI events occur only sporadically and in an uncontrolled fashion, it is difficult to identify the causes for this phenomenon and to develop solutions to suppress it. Some countermeasures exist that OEMs can use to avoid LSPI, such as load limiting, but these have drawbacks.

Because of the thermodynamic relationship of pressure, temperature and volume for processes which occur in an internal-combustion engine (ICE), and their relationship to ideal efficiency and efficiency-limiting phenomena e.g. knock in spark-ignition engines, changing the thermo-chemical properties of the in-cylinder charge should be considered as an increment in the development of the ICE engine for future efficiency improvements. Exhaust gas recirculation (EGR) in spark-ignited gasoline engines is one increment that has been made to alter the in-cylinder charge. EGR gives proven thermal efficiency benefits for SI engines which improve vehicle fuel economy, as demonstrated through literature and production applications. The thermal efficiency benefit of EGR is due to lower in-cylinder temperatures, reduced heat transfer and reduced pumping losses. The next major increment could be modifying the constituents of the EGR stream, potentially through the means of a membrane.

The spark ignition (SI) engine has been known to exhibit several different abnormal combustion phenomena, such as knock or pre-ignition, which have been addressed with improved engine design or control schemes. However, in highly boosted SI engines, Low-Speed Pre-Ignition (LSPI), a pre-ignition event typically followed by heavy knock, has developed into a topic of major interest due to its potential for engine damage. Previous experiments associated increases in hydrocarbon emissions with the blowdown event of an LSPI cycle [1]. Also, the same experiments showed that there was a dependency of the LSPI activity on fuel and/or lubricant compositions [1]. Based on these findings it was hypothesized that accumulated hydrocarbons play a role in LSPI and are consumed during LSPI events. A potential source for accumulated HC is the top land piston crevice.