Xiaoye Han

Clean combustion enabling with ethanol on a dual-fuel compression ignition engine

In this work, ethanol is applied as the main energy source (up to 95%) on a high compression ratio (18.2:1) diesel engine for improvements in engine efficiency and exhaust emissions, especially at high engine loads. The intake port injection is applied for ethanol fuel delivery along with directly injected diesel pilots as the ignition source. In order to investigate the impact of ethanol on diesel engines operating in the dual-fuel mode, systematic engine experiments are carried out to study the combustion process, engine emissions, and fuel efficiency. The test results indicate that at medium engine loads (8–10 bar indicated mean effective pressure), the increasing use of ethanol offers substantially enhanced homogeneity of the cylinder charge and leads to a greater extent of premixed burning; as a result, the smoke emissions reduce drastically compared to those of the diesel baseline tests. However, the increasing use of ethanol generally results in higher incomplete combustion products. The near-top dead center injected diesel pilots are effective to control the ignition timing and combustion phasing, which provides desirable combustion controllability. At high engine loads, the clean combustion is enabled through the optimization of the engine intake pressure, exhaust gas recirculation, and the fuel ratio to achieve NOx emissions < 0.2 g/kW h and smoke emissions < 0.01 g/kW h. The load capability of the engine operating on ethanol as the primary energy source is demonstrated up to the engine full load (19.5 bar indicated mean effective pressure) with low NOx (0.2–0.7 g/kW h) and smoke ( <1 FSN) emissions.

Study of Cylinder Charge Control for Enabling Low Temperature Combustion in Diesel Engines

Suitable cylinder charge preparation is deemed critical for the attainment of a highly homogeneous, diluted, and lean cylinder charge which is shown to lower the flame temperature. The resultant low temperature combustion (LTC) can simultaneously reduce the NOx and soot emissions from diesel engines. This requires sophisticated coordination of multiple control systems for controlling the intake boost, exhaust gas recirculation (EGR), and fueling events. Additionally, the cylinder charge modulation becomes more complicated in the novel combustion concepts that apply port injection of low reactivity alcohol fuels to replace the diesel fuel partially or entirely. In this work, experiments have been conducted on a single cylinder research engine with diesel and ethanol fuels. The test platform is capable of independently controlling the intake boost, EGR rates, and fuelling events. Effects of these control variables are evaluated with diesel direct injection and a combination of diesel direct injection and ethanol port injection. Data analyses are performed to establish the control requirements for stable operation at different engine load levels with the use of one or two fuels. The sensitivity of the combustion modes is thereby analyzed with regard to the boost, EGR, fuel types and fueling strategies. Zero-dimensional cycle simulations have been conducted in parallel with the experiments to evaluate the operating requirements and operation zones of the LTC combustion modes. Correlations are generated between air-fuel ratio (λ), EGR rate, boost level, in-cylinder oxygen concentration and load level using the experimental data and simulation results. Development of a real-time boost-EGR set-point determination to sustain the LTC mode at the varying engine load levels and fueling strategies is proposed.Copyright

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.

An Analysis of the Production of Hydrogen and Hydrocarbon Species by Diesel Post Injection Combustion

The effects of post injection on the combustion efficiency, exhaust emissions, and in-cylinder hydrogen generation were experimentally investigated in a modern heavy duty diesel engine. As the post injection was moved away from top dead center (TDC), the test results generally showed increasing carbon monoxide (CO) and total hydrocarbons (THC), fairly constant nitrogen oxide (NOx) emissions while the smoke emissions were more sensitive to the post injection timing. Hydrogen production was observed to be higher at later post injection timings. In a majority of instances, hydrogen production and carbon monoxide formation were very well correlated. Additional tests explored the effects of the overall air-to-fuel ratio on the in-cylinder hydrogen production and the experimental results indicated that a lower air-to-fuel ratio seemed to promote the in-cylinder generation of hydrogen. However, the increased hydrogen production was offset by less efficient power production from the post injection combustion. A Fourier transform infrared (FTIR) spectroscopy analysis of hydrocarbon emissions was carried out in an attempt to determine the effects of diesel post injection timing on individual light hydrocarbon species.Copyright

Characterization of N-Butanol High Pressure Injection From Modern Common Rail Injection System

Increasing attention has being paid to alternative fuels that have the potential to reduce overall greenhouse gas emissions and fossil fuel dependence. The alcohol fuel n-butanol, as one of the advanced biofuels, can be potentially utilized as a partial or complete substitute for the diesel fuel in diesel engines. Experimental results from literature, as well as from the authors’ previous research, have shown promising trend of low soot and nitrogen oxides emissions from the combustion with n-butanol high pressure direct injection. However, due to the significant fuel property differences between n-butanol and diesel, the fuel delivery mechanism and combustion control algorithm need to be optimized for n-butanol use. A better understanding of the high pressure n-butanol injection characteristics, such as the injector opening/closing delays and spray droplet sizes, can provide the guidance for the control optimization and insights to the empirical observations of engine combustion and emissions. Meanwhile, the experimental data could be used for the model development of the n-butanol high pressure fuel injection events.In this work, injection rate measurement, high-speed video direct imaging, and phase Doppler anemometry (PDA) analysis of neat n-butanol and diesel fuel have been conducted with a light-duty high pressure common-rail fuel injection system. The injection rate measurement was performed with an offline injection rate analyzer at 20 bar backpressure to obtain the key parameters of the injector opening/closing delays, and the instantaneous pressure rise. The spray direct imaging was carried out in a pressurized chamber, and the PDA measurement was conducted on a test bench at ambient temperature and pressure. The injector dynamics and spray behavior with respect to the different fuels, variation of injection pressures, and variation of injection durations are discussed.Copyright

A Study of Combustion Inefficiency in Diesel LTC and Gasoline-Diesel RCCI via Detailed Emission Measurement

Reduction of engine-out NOx emissions to ultra-low levels is facilitated by enabling low temperature combustion (LTC) strategies. However, there is a significant energy penalty in terms of combustion efficiency as evidenced by the accompanying high levels of hydrocarbon (HC), carbon monoxide (CO), and hydrogen emissions. In this work, the net fuel energy lost as a result of incomplete combustion in two different LTC regimes is studied. The first LTC strategy, partially premixed compression ignition (PPCI), is investigated using a single, high pressure, in-cylinder injection of diesel fuel along with the application of exhaust gas recirculation (EGR). The second strategy includes dual-fuel application – reactivity controlled compression ignition (RCCI) of port injected gasoline and direct injected diesel. Moderate to high levels of EGR are necessary during engine operation in either of the two LTC pathways. A detailed analysis of the incomplete combustion products was conducted while the engine was operated in the aforementioned LTC modes. Speciation analysis of hydrocarbons was performed by sampling the exhaust gas in an FTIR. The total HC and the CO emissions were simultaneously measured using an FID and an NDIR, respectively. The production of hydrogen during the combustion process was also evaluated using a mass spectrometer. Engine tests were conducted at a baseline load level of 10 bar IMEP in the PPCI and RCCI modes. Load extension tests, up to 17 bar IMEP, were then conducted in the RCCI mode by increasing the gasoline-to-diesel fuel ratio. Test results indicated that CO, H2, and light HC made up for most of the combustion in-efficiency in the PPCI mode while heavier HC and aromatics were significantly higher in the RCCI mode.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.

Multi-Coil High Frequency Spark Ignition to Extend Diluted Combustion Limits

A reliable ignition process is desirable for the ignition of a lean and/or EGR diluted cylinder charge commonly adopted to achieve clean and efficient engine combustion. In this work, ignition of a diluted propane-air mixture is investigated using a high energy spark ignition system. Efforts are dedicated towards development of a novel ignition system that improves the ignition quality whilst keeping within the bounds of current spark ignition hardware to facilitate potential application in future clean combustion engines. A multi-coil ignition system was developed to adjust the spark energy and the discharge pattern. With enhanced primary voltage up to 120 V, a multi-spark strategy with frequency up to 20 kHz can be implemented. The combustion visualization results show that the application of both multi-coil and multi-spark strategy can promote the flame propagation. The high frequency multi-spark strategy shows better ignition quality compared to a single-spark strategy. With discharge energy enhancement by coupling more coils, the ignition success rate is increased under diluted mixture conditions. The diluted combustion limits are therefore extended with the help of these spark strategies.

A Preliminary Study of the Spark Characteristics for Unconventional Cylinder Charge With Strong Air Movement

Detailed fundamental understanding of spark discharge under strong air movement condition is crucial to optimize the ignition systems for stratified charge engines. In this paper, extensive bench tests of spark discharge under strong air movement condition are conducted by means of both optical and electrical diagnosis. Strong correlations between the physical structures of spark plasma channel and the gas velocity are found in this paper. The spark heat dissipation distance, the plasma stretched distance and the plasma area under various flow velocities are analyzed. The resistance between the electrode gaps is increased with the enhancement of flow velocity. As a result, the discharge voltage is enhanced, while the discharge duration is shortened. When the flow velocity is enhanced substantially, restrikes of spark discharge are observed. The increasing rate of the discharge voltage before the first restrike is found to be a 2-order polynomial relation to the gas velocity. With the enhancement of flow velocity, the delivered discharge energy increases linearly at the velocity below 25m/s, while it tends to be maintained at the higher flow velocities. Both the increase of the electrode gap size and the flow velocity shorten the spark discharge duration.Copyright

Preliminary Investigation of Direct Injection Neat n-Butanol in a Diesel Engine

The characteristics of combustion, emissions, and thermal efficiency of a diesel engine with direct injection neat n-butanol were investigated. Tests were conducted on a single cylinder water-cooled four stroke direct injection diesel engine. The engine ran at a load of 6.5 ∼ 8.0 bar IMEP at 1500 rpm engine speed and the injection pressure was controlled to 900 bar. The intake boost pressure, injection timing and EGR rate were adjusted to investigate the engine performance. The test results showed that significantly longer ignition delays were possible when using butanol compared to diesel fuel. Butanol usage generally led to a rapid heat release in a short period, resulting in excessively high pressure rise rate. The pressure rise rate was reduced by retarding the injection timing. The butanol injection timing was limited by misfire and pressure rise rate. Thus, the ignition timing controllable window by injection timing was much narrower than that of diesel. The neat butanol combustion produced near zero soot and very low NOx emissions even at low EGR rate. The tests demonstrated that neat butanol had the potential to achieve ultra-low emissions. However, challenges related to reducing the pressure rise rate and improving the ignition controllability were identified.Copyright