Graham T. Reader

Diesel engine exhaust gas recirculation--a review on advanced and novel concepts

Exhaust gas recirculation (EGR) is effective to reduce nitrogen oxides (NOx) from Diesel engines because it lowers the flame temperature and the oxygen concentration of the working fluid in the combustion chamber. However, as NOx reduces, particulate matter (PM) increases, resulting from the lowered oxygen concentration. When EGR further increases, the engine operation reaches zones with higher instabilities, increased carbonaceous emissions and even power losses. In this research, the paths and limits to reduce NOx emissions from Diesel engines are briefly reviewed, and the inevitable uses of EGR are highlighted. The impact of EGR on Diesel operations is analyzed and a variety of ways to implement EGR are outlined. Thereafter, new concepts regarding EGR stream treatment and EGR hydrogen reforming are proposed.

A Thermal Response Analysis on the Transient Performance of Active Diesel Aftertreatment

Diesel fueling and exhaust flow strategies are investigated to control the substrate temperatures of diesel aftertreatment systems. The fueling control includes the common-rail post injection and the external supplemental fuel injection. The post injection pulses are further specified at the early, mid, or late stages of the engine expansion stroke. In comparison, the external fueling rates are moderated under various engine loads to evaluate the thermal impact. Additionally, the active-flow control schemes are implemented to improve the overall energy efficiency of the system. In parallel with the empirical work, the dynamic temperature characteristics of the exhaust system are simulated one-dimensionally with in-house and external codes. The dynamic thermal control, measurement, and modeling of this research intend to improve the performance of diesel particulate filters and diesel NOx absorbers.

A Thermal Analysis of Active-flow Control on Diesel Engine Aftertreatment

One-dimensional transient modeling techniques are adapted to analyze the thermal behavior of lean-burn after-treatment systems when active flow control schemes are applied. The active control schemes include parallel alternating flow, partial restricting flow, and periodic flow reversal (FR) that are found to be especially effective to treat engine exhausts that are difficult to cope with conventional passive flow converters. To diesel particulate filters (DPF), lean NOx traps (LNT), and oxidation converters (OC), the combined use of active flow control schemes are identified to be capable of shifting the exhaust gas temperature, flow rate, and oxygen concentration to more favorable windows for the filtration, conversion, and regeneration processes. Comparison analyses are made between active flow control and passive flow control schemes in investigating the influences of gas flow, heat transfer, chemical reaction, oxygen concentration, and converter properties. Some of the simulation results, such as the periodic flow reversal results, are largely in agreement with the previous empirical observation.

Effects of Postinjection Application with Late Partially Premixed Combustion on Power Production and Diesel Exhaust Gas Conditioning

The effects of postinjection with late partially premixed charge compression ignition (PCCI) were investigated with respect to diesel exhaust gas conditioning and potential power production. Initial tests comparing postinjection application with PCCI to that with conventional diesel high temperature combustion (HTC) indicated the existence of similar trends in terms of carbon monoxide (CO), total unburned hydrocarbon (THC), oxides of nitrogen (NOx), and smoke emissions. However, postinjection in PCCI cycles exhibited lower NOx and smoke but higher CO and THC emissions. With PCCI operation, the use of postinjection showed much weaker ability for raising the exhaust gas temperature compared to HTC. Additional PCCI investigations generally showed increasing CO and THC, relatively constant NOx, and decreasing smoke emissions, as the postinjection was shifted further from top dead center (TDC). Decreasing the overall air-to-fuel ratio resulted in increased hydrogen content levels but at the cost of increased smoke, THC and CO emissions. The power production capabilities of early postinjection, combined with PCCI, were investigated and the results showed potential for early postinjection power production.

Fuel efficiency analysis and peak pressure rise rate improvement for neat n-butanol injection strategies

Engine tests were conducted to investigate the efficiency and the peak pressure rise rate performance of different fuel injection strategies for the direct injection of neat n-butanol in a compression ignition engine. Three different strategies were tested: a single-shot injection; a pilot injection; a post-injection. A single-shot injection timing sweep revealed that early injections had the highest indicated efficiency while late injections reduced the peak pressure rise rate at the cost of a slightly reduced thermal efficiency. Delayed single-shot injections also had increased emissions of nitrogen oxides, total hydrocarbon and carbon monoxide. Addition of a pilot injection had a negative effect on the peak pressure rise rate. Because of the low cetane number of butanol and the relatively lean and well-premixed air–fuel mixture, the pilot injection failed to autoignite and instead ignited simultaneously with the main injection. This resulted in slightly increased peak pressure rise rates and significantly increased unburned butanol hydrocarbon emissions. Conversely, the use of an early post-injection produced a noticeable engine power output and allowed the main injection to be shortened and the peak pressure rise rate to be substantially reduced. However, relatively early post-injections slightly reduced the indicated efficiency and increased the nitrogen oxide emissions and the carbon monoxide emissions compared with the single-shot injection strategy. These results recommended the use of a single-shot injection for low loads and medium loads owing to a superior thermal efficiency and suggested that the application of a post-injection may be more suited to high-load conditions because of the substantially reduced peak pressure rise rates.

Adaptive Combustion Control to Improve Diesel HCCI Cycle Fuel Efficiency

Previous work indicates that the lowered combustion temperature in diesel engines is capable of reducing nitrogen oxides and soot simultaneously, which can be implemented by the heavy use of exhaust gas recirculation or the homogeneous charge compression ignition (HCCI) type of combustion. However, the fuel efficiency of the low temperature combustion cycles is commonly compromised with high levels of hydrocarbon and carbon monoxide emissions. Additionally, in cases of diesel HCCI cycles, the combustion process may even occur before the piston completes the compression stroke, which may cause excessive efficiency reduction and combustion roughness. Adaptive control strategies are applied to precisely navigate and stabilize the engine cycles and to better phase and complete the combustion process. The impact of heat release phasing, duration, shaping, and splitting on the thermal efficiency has also been analyzed with zero-dimensional engine cycle simulations. The correlations between the cylinder pressure and the heat release curves have been characterized to facilitate model based control. The empirical set-up and cases of applications are provided.Copyright

Ethanol diesel dual fuel clean combustion with FPGA enabled control

Sophisticated engine controls have progressively become vital enablers for implementing clean and efficient combustion. The low temperature combustion in diesel engines is a viable combustion mode that offers ultra-low nitrogen oxides and dry soot emissions, yet only feasible under tightly controlled operating conditions. In this work, the dual fuel application of ethanol and diesel is studied for clean and efficient combustion. A set of real-time controllers has been configured to control the common-rail pressure and injection events, in concert with the use of two fuels in a high compression ratio diesel engine. An improved control algorithm has been implemented into the field programmable gate array devices to promptly execute the injection commands of the port and direct injection events. Such reliable and prompt control of fuel injection has been identified as critical to safely enable simultaneously low nitrogen oxides and soot combustion, especially when excessive or inadequate rate of exhaust gas recirculation is imminent. High load clean combustion was achieved with the improved control system.

Preliminary Energy-Efficiency Analysis on Multi-Pulse Injection Schedule in a Diesel Engine

The multi-pulse fuel injection in a diesel engine is considered an effective way to reduce nitrogen oxides (NOx) emissions by heat-release shaping. In this research a preliminary energy efficiency analysis has been conducted for various split injection rates and schedules using the in-house and the commercial engine simulation software. Theoretical findings have been validated using experimentally obtained cylinder pressure data for various injection timings from a single-cylinder engine. The theoretical analysis on the shape of heat- release has been made to evaluate the energy efficiency of the post injection pulses on the engine exhaust temperature increases. An investigation of the cycle-to-cycle variation has also been performed for the measured cylinder pressure data.Copyright

Preliminary Energy Efficiency Analysis of an EGR Fuel-Reformer

Diesel engine exhausts commonly contain a high level of surplus oxygen and a significant amount of thermal energy. In this study the authors have theoretically investigated a way of utilizing the thermal energy and the surplus oxygen of exhaust gases to produce gaseous fuel in a rich combustor placed in an exhaust gas recirculation (EGR) loop. In the rich combustor, a small amount of diesel fuel will be catalytically reformed on a palladium/platinum based catalyst to produce hydrogen and carbon monoxide. Since the catalytic EGR reformer is incorporated in the EGR loop, it enables the partial recovery of exhaust heat. The gaseous fuel produced in the rich combustor can be brought back into the engine in a pre-mixed condition, potentially reducing soot formation. The preliminary energy efficiency analysis has been performed by using CHEMKIN and an in-house engine simulation software SAES. This research is the prelude of the experimental work to be performed at the University of Windsors Clean Diesel Lab.

Effect of Hydrogen Peroxide on Premixed Iso-Octane/Air Combustion

The effect of hydrogen peroxide (H2 O2 ) on premixed isooctane/air combustion was numerically investigated using detailed chemical kinetics (Peters’ mechanism) via CHEMKIN. Two cases were examined: one-dimensional, planar, adiabatic, premixed flame, which is of fundamental importance to many combustion systems including internal combustion engines, and zero-dimension, adiabatic Homogeneous Charge Compression Ignition (HCCI). Initial conditions investigated were at 298 K and 1 atm for the premixed flame and 343 K and 1 atm for the HCCI. The effects of H2 O2 addition on combustion characteristics including burning velocity, flame temperature, species concentration and ignition delay were deduced. Hydrogen peroxide was utilized as a possible means of emissions reduction. Specifically, the potential of CO reduction due to increased intermediate OH species was studied. The utilization of H2 O2 as a means of controlling ignition timing was also explored.Copyright