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Effects of fuel physical and chemical properties on combustion and emissions were investigated on both metal and optical diesel engines. The new generation oxygenated biofuels, n-butanol and DMF (2,5-dimethylfuran) were blended into diesel fuel with 20% volume fraction and termed as Butanol20 and DMF20 respectively. The exhaust gas recirculation (EGR) rates were varied from zero to ∼60% covering both conventional and low temperature combustion. Meanwhile, the reference fuels such as n-heptane, cetane, and iso-cetane were also used to isolate the effects of different fuel properties on combustion and emissions. In addition, to clarify the effects of oxygenated structures on combustion and emissions, a fundamental partially premixed burner was also used. Results based on metal and optical diesel engines show that fuel cetane number is the dominated factor to affect the auto-ignition timing and subsequent combustion process.

Reactivity Controlled Compression Ignition (RCCI) has been shown to be an attractive concept to achieve clean and high efficiency combustion. RCCI can be realized by applying two fuels with different reactivities, e.g., diesel and gasoline. This motivates the idea of using a single low reactivity fuel and direct injection (DI) of the same fuel blended with a small amount of cetane improver to achieve RCCI combustion. In the current study, numerical investigation was conducted to simulate RCCI and HCCI combustion and emissions with various fuels, including gasoline/diesel, iso-butanol/diesel and iso-butanol/iso-butanol+di-tert-butyl peroxide (DTBP) cetane improver. A reduced Primary Reference Fuel (PRF)-iso-butanol-DTBP mechanism was formulated and coupled with the KIVA computational fluid dynamic (CFD) code to predict the combustion and emissions of these fuels under different operating conditions in a heavy duty diesel engine.

An experimental study is carried out to compare the effects of high-pressure-loop, low-pressure-loop and dual-loop exhaust gas recirculation systems (HPL-EGR, LPL-EGR and DL-EGR) on the combustion characteristics, thermal efficiency and emissions of a diesel engine. The tests are conducted on a six-cylinder turbocharged heavy-duty diesel engine under various operating conditions. The low-pressure-loop portion (LPL-Portion) of DL-EGR is swept from 0% to 100% at several constant EGR rates, and the DL-EGR is optimized based on fuel efficiency. The results show that the LPL-EGR can attain the highest gross indicated thermal efficiency (ITEg) in the three EGR systems under all the tested conditions. At a middle load of 0.95 BMEP, 1660 r/min, the pumping losses of LPL-EGR lead to the lowest BTE among the EGR systems. The HPL-EGR can achieve the best brake thermal efficiency (BTE) and emissions within the EGR rate of 22.5% mainly due to the reduced pumping losses.

A comprehensive investigation on the impact of piston design on scavenging and combustion in an opposed- piston, opposed-cylinder (OPOC) two-stroke engine is carried out and presented in this paper. Two-stroke engines, in general, have superior power densities and brake thermal efficiencies. Compared with opposed-piston (OP) engines, the OPOC architecture comprises only one crankshaft instead of two, and all the forces generated on the piston go to this one crankshaft via a common bearing, thus making the engine structure inherently simple, lightweight, compact and efficient. Due to the piston motion of the OPOC engine, two opposing injectors were mounted at the center of the cylinder wall for each cylinder. This unique feature posed challenges on air entrainment for air/fuel mixing because of the inherent limited space for injection spreading angle near top-dead-center (TDC).

Alcohols, because of their potential to be produced from renewable sources and their characteristics suitable for clean combustion, are considered potential fuels which can be blended with fossil-based gasoline for use in internal combustion engines. As such, n-butanol has received a lot of attention in this regard and has shown to be a possible alternative to pure gasoline. The main issue preventing butanol's use in modern engines is its relatively high cost of production. Acetone-Butanol-Ethanol (ABE) fermentation is one of the major methods to produce bio-butanol. The goal of this study is to investigate the combustion characteristics of the intermediate product in butanol production, namely ABE, and hence evaluate its potential as an alternative fuel. Acetone, n-butanol and ethanol were blended in a 3:6:1 volume ratio and then splash blended with pure ethanol-free gasoline with volumetric ratios of 0%, 20%, 40% to create various fuel blends.

Acetone-Butanol-Ethanol (ABE), an intermediate product in the ABE fermentation process for producing bio-butanol, is considered a promising alternative fuel because it not only preserves the advantages of oxygenated fuel which typically emit less pollutants compared to conventional diesel, but also lowers the cost of fuel recovery for each individual component during the fermentation. With the development of advanced ABE fermentation technology, the volumetric percentage of acetone, butanol and ethanol in the bio-solvents can be precisely controlled. In this respect, it is desirable to estimate the performance of different ABE blends to determine the best blend and optimize the production process accordingly. ABE fuels with different component ratio, (A: B: E: 6:3:1; 3:6:1; 0:10:0, vol. %), were blended with diesel and tested in a constant volume chamber.

The purpose of this study is to investigate the possibility of acetone-butanol-ethanol (ABE) blended with diesel without further component recovery which has high costs blocking the industrial-scale production of bio-butanol. The combustion characteristics of ABE and diesel blends were studied in a constant volume chamber. In this study, 50% and 80% vol. ABE (without water) were mixed with diesel and the vol. % of acetone, butanol and ethanol were kept at 30%, 60% and 10% respectively. The in-cylinder pressure was recorded using a pressure transducer and the time-resolved natural luminosity was captured by high speed imaging. Combustion visualization using laser diagnostics would provide crucial fundamental information of the fuel's combustion characteristics. With the different percentage of the ABE blended in the diesel, the soot oxidation, the ignition delay and the soot lift-off length were studied in this work.

In the new combustion strategies such as RCCI and dual-fuel combustion, the diesel pilot injection plays a pivotal role as it determines the ignition characteristics of the mixture and ultimately the combustion and emission performance. In this regard, equivalence ratio distribution resulted from the pilot injection becomes very important. In this work, computation study is carried out using KIVA-3V to simulate the engine compression stroke from intake valve close (IVC) to close to TDC so as to investigate the impact of piston geometry, injection start timing and flow initialization on the equivalence ratio distribution from a pilot injection in HSDI engine.

In order to achieve high efficiency and clean combustion indiesel engines, many advanced combustion concepts have been developed to simultaneously reduce NOx and soot emissions with high efficiency. However, the benefits of these combustion modes are limited to low loads because the energy release ratesaretoo fast at high loads. Recently, Dual-fuel highly premixed charge combustion (HPCC) strategies with the port injection of gasoline and direct injection of diesel have demonstrated advantages in terms of extending the operating range by the flexible control of fuel chemical reactivity and charge stratification. However, the extension to high-load in a turbocharged multi-cylinder diesel engine with the HPCC is a critical challenge due to excessive pressure rise rates. Mean while it suffers from the excessive of CO/HC emissions at low loads.

This work concerns the oxidation of biodiesel surrogates in a CI engine. An experimental study has been carried out in a single-cylinder common-rail CI engine with soybean biodiesel and two biodiesel surrogates containing neat methyl decanoate and methyl decanoate/n-heptane blends. Tests have been conducted with various intake oxygen concentrations ranging from 21% to approximately 9% at intake temperatures of 25°C and 50°C. The results showed that the ignition delay and smoke emissions of neat methyl decanoate were closer to that of soybean biodiesel as compared with methyl decanoate/n-heptane blends. A reduced chemical kinetic mechanism for the oxidation of methyl decanoate has been developed and applied to model internal combustion engines. A KIVA code, coupled with the Chemkin chemistry solver, was used as the computational platforms. The effects of various intake oxygen concentrations on the in-cylinder emissions of OH and soot were discussed.

This paper describes numerical simulations that compare the performance of two combustion CFD models against experimental data, and evaluates the effects of combustion and spray model constants on the predicted combustion and emissions under various operating conditions. The combustion models include a Characteristic Time Combustion (CTC) model and CHEMKIN with reduced chemistry models integrated in the KIVA-3Vr2 CFD code. The diesel spray process was modeled using an updated version of the KH-RT spray model that features a gas jet submodel to help reduce numerical grid dependencies, and the effects of both the spray and combustion model constants on combustion and emissions were evaluated. In addition, the performance of two soot models was compared, namely a two-step soot model, and a more detailed model that considers soot formation from PAH precursors.

Comparisons have been made between dual-fuel (80% port-injection gasoline and 20% direct-injection diesel by mass) Highly Premixed Charge Combustion (HPCC) and blended-fuel (80% gasoline and 20% diesel) Low Temperature Combustion (LTC) modes on a 1-L single-cylinder test engine. In the HPCC mode, both early-injection (E-HPCC) and late-injection (L-HPCC) of diesel have been used. The comparisons have been conducted with a fixed fuel injection rate of 50 mg/cycle at 1500 rpm, and with the combustion phasing fixed (by adjusting the injection timing) so that the 50% heat release point (CA50) is at 8° ATDC. The rapid heat release process of LTC leads to the highest maximum pressure rise rate (MPRR). A two-peak heat release process is observed in L-HPCC, resulting in a lower MPRR. The heat release rate and MPRR values for the E-HPCC are comparable to the L-HPCC values. The EHPCC mode provides the lowest NOX emission. The soot emissions for all three modes are low.

The combustion and emission characteristics of a diesel engine running on butanol-diesel blends were investigated in this study. The blending ratio of n-butanol to diesel was varied from 0 to 40 vol% using an increment of 10 vol%, and each blend was tested on a 2.7 L V6 common rail direction injection diesel engine equipped with an EGR system. The test was carried out under two engine loads at a constant engine speed, using various combinations of EGR ratios and injection timings. Test results indicate that n-butanol addition to engine fuel is able to substantially decrease soot emission from raw exhaust gas, while the change in NOx emissions varies depending on the n-butanol content and engine operating conditions. Increasing EGR ratio and retarding injection timing are effective approaches to reduce NOx emissions from combustion of n-butanol-diesel blends.

Biodiesel is a widely used biofuel in diesel engines, which is of particular interest as a renewable fuel because it possesses the similar properties as the diesel fuel. The pure soybean biodiesel was tested in an optical constant volume combustion chamber using natural flame luminosity and forward illumination light extinction (FILE) methods to explore the combustion process and soot distribution at various ambient temperatures (800 K and 1000 K) and oxygen concentrations (21%, 16%, 10.5%). Results indicated that, with a lower ambient temperature, the autoignition delay became longer for all three oxygen concentrations and more ambient air was entrained by spray jet and more fuel was burnt by premixed combustion. With less ambient oxygen concentration, the heat release rate showed not only a longer ignition delay but also longer combustion duration.

The influence of different combustion chamber configuration, intake temperature, and coolant temperature on HCCI combustion processes were investigated in a single-cylinder optical engine. Two-dimensional images of the chemiluminescence were captured using an intensified CCD camera in order to understand the spatial distribution of the combustion. N-heptane was used as the test fuel. Three combustion chamber geometries with different squish lip, salient, orthogonal, reentrant shape, referred as V-type, H-type, and A-type respectively, were used in this study. Intake temperature was set to 65°C and 95°C, while coolant temperature was set to 85°C. The experimental data consisting of the in-cylinder pressure, heat release rate, chemiluminescence images all indicated that the different combustion chamber geometries result in different turbulence intensity in the combustion chamber, and thus affect the auto-ignition timing, chemiluminescence intensity, and combustion processes.

In this paper, experimental investigation on spray atomization and droplet dynamics inside a thermostatic expansion valve (TXV), a component commonly used in vehicle refrigeration system, was conducted. A needle and an orifice were copied from a commercial TXV and machined to be mounted inside a chamber with optical access so that the flow inside the TXV is simulated and visualized at the same time. The break-up and atomization of the refrigerant were documented near the downstream of the orifice under different feed conditions for two TXV with different geometry. A Phase Doppler Anemometry (PDA) system was used later to measure the size and velocity of atomized refrigerant droplets. The results showed that the droplet size variation along the radial direction is slightly decreased at near downstream and increased at farther downstream due to the coalescence.

HCCI/PCCI combustion concepts have been demonstrated for both high brake thermal efficiency and low engine-out emissions. However, these advanced combustion concepts still could not be fully utilized partially due to the limitations of conventional fixed spray angle nozzle designs for issues related to wall wetting for early injections. The micro-variable circular orifice (MVCO) fuel injector provides variable spray angles, variable orifice areas, and variable spray patterns. The MVCO provides optimized spray patterns to minimize combustion chamber surface-wetting, oil dilution and emissions. Designed with a concise structure, MVCO can significantly extend the operation maps of high efficiency early HCCI/PCCI combustion, and enable optimization of a dual-mode HCCI/PCCI and Accelerated Diffusion Combustion (ADC) over full engine operating maps. The MVCO variable spray pattern characteristics are analyzed with high speed photographing.

Ternary blends of butanol-biodiesel-diesel with different blending ratios were tested inside a constant volume chamber under various ambient temperatures so as to investigate the spray and combustion characteristics of the fuels. Applying the high speed imaging, a sudden drop in spray penetration was observed at ambient temperature of 800 K and 900 K for fuels with certain blending ratio, but not at 1000 K and 1200 K. When the spray penetration of the butanol-biodiesel-diesel blends was compared to that of the biodiesel-diesel blends under non-combusting environment, a sudden drop in spray penetration length was also observed at 1100 K. The results indicated that for the non-combusting case, the tip of the spray jet erupted into a plume sometime after injection for the butanol-biodiesel-diesel blend at an ambient temperature of 1100 K. Such phenomenon was not seen with the biodiesel-diesel blend, neither with the same fuel but at a lower ambient temperature of 900 K.

A very competitive alcohol for use in diesel engines is butanol. Butanol is of particular interest as a renewable bio-fuel, as it is less hydrophilic and it possesses higher heating value, higher cetane number, lower vapor pressure, and higher miscibility than ethanol or methanol. These properties make butanol preferable to ethanol or methanol for blending with conventional diesel or gasoline fuel. In this paper, the spray and combustion characteristics of pure n-butanol fuel was experimentally investigated in a constant volume combustion chamber. The ambient temperatures were set to 1000 K, and three different oxygen concentrations were set to 21%, 16%, and 10.5%. The results indicate that the penetration length reduces with the increase of ambient oxygen concentration. The combustion pressure and heat release rate demonstrate the auto-ignition delay becomes longer with decreasing of oxygen concentrations.

Exhaust Gas Recirculation (EGR) is an important parameter for control of diesel engine combustion, especially to achieve ultra low NOx emissions. In this paper, the effects of EGR on engine emissions and engine efficiency have been investigated in a heavy-duty diesel engine while changing combustion control parameters, such as injection pressure, injection timing, boost, compression ratio, oxygenated fuel, etc. The engine was operated at 1400 rpm for a cycle fuel rate of 50mg. The results show that NOx emissions strongly depend on the EGR rate. The effects of conventional combustion parameters, such as injection pressure, injection timing, and boost, on NOx emissions become small as the EGR rate is increased. Soot emissions depend strongly on the ignition delay and EGR rate (oxygen concentration). Soot emissions can be reduced by decreasing the compression ratio, increasing the injection pressure, or burning oxygenated fuel.