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Homogeneous Charge Compression Ignition (HCCI) has been shown as a promising technique for simultaneous NOx and soot reduction while maintaining diesel-like efficiency. Although HCCI has been shown to yield very low emissions levels, spray-wall impingement and high pressure rise rates can be problematic due to the early injection timings necessary for certain HCCI operations. To address spray-wall impingement, an Adaptive Injection Strategy (AIS) was employed. This strategy uses multiple pulses at both low and high injection pressures to prepare an optimal in-cylinder mixture. A unique Variable Pressure Pulse (VPP) was developed to investigate the AIS concept experimentally. The VPP has the capability of delivering multiple injections at both low and high injection pressures (∼100 bar and ∼1000 bar respectively) through a single injector in the same engine cycle. Comparisons were made between model predictions and engine experiments using the VPP system.

A study of partially premixed combustion (PPC) with non-oxygenated 91 pump octane number1 (PON) commercially available gasoline was performed using a heavy-duty (HD) compression-ignition (CI) 2.44 l Caterpillar 3401E single-cylinder oil test engine (SCOTE). The experimental conditions selected were a net indicated mean effective pressure (IMEP) of 11.5 bar, an engine speed of 1300 rev/min, an intake temperature of 40°C with intake and exhaust pressures of 200 and 207 kPa, respectively. The baseline case for all studies presented had 0% exhaust gas recirculation (EGR), used a dual injection strategy a -137 deg ATDC pilot SOI and a -6 deg ATDC main start-of-injection (SOI) timing with a 30/70% pilot/main fuel split for a total of 5.3 kg/h fueling (equating to approximately 50% load). Combustion and emissions characteristics were explored relative to the baseline case by sweeping main and pilot SOI timings, injection split fuel percentage, intake pressure, load and EGR levels.

The simultaneous reduction of particulate matter (PM) and nitrous oxides (NOx) emissions form diesel exhaust is key to current research activities. Although various technologies have been introduced to reduce emissions from diesel engines, the in-cylinder reduction of PM and NOx due to improved combustion mechanisms will continue to be an important field in research and development of modern diesel engines. Furthermore increasing prices and question over the availability of diesel fuel derived from crude oil has introduced a growing interest. Hence it is most likely that future diesel engines will be operated on pure biodiesel and/or blends of biodiesel and crude oil-based diesel. In this study the performance of different biodiesel blends under low temperature combustion conditions (i.e., high exhaust gas recirculation and advanced fuel injection schemes) was investigated.

Two advanced combustion models have been validated with the KIVA-3V Release 2 code in the context of two-stage combustion in a heavy duty diesel engine. The first model uses CHEMKIN to directly integrate chemistry in each computational cell. The second model accounts for flame propagation with the G-equation, and CHEMKIN predicts autoignition and handles chemistry ahead of and behind the flame front. A Damköhler number criterion was used in flame containing cells to characterize the local mixing status and determine whether heat release and species change should be a result of flame propagation or volumetric heat release. The purpose of this criterion is to make use of physical and chemical time scales to determine the most appropriate chemistry model, depending on the mixture composition and thermodynamic properties of the gas in each computational cell.

The development of a new Nitric Oxide (NOx) reaction mechanism has been conducted by adding species, including hydrogen cyanide (HCN) and the CH radical to a reduced chemistry diesel combustion model. The additional chemical reactions were added to the ERC's reduced 12-step NOx mechanism, which consists of N, NO, N2O, and NO2. The new NOx mechanism was implemented into the KIVA/ERC-CHEMKIN code and was found to be able to predict the experimentally observed trend that the amount of engine-out NOx decreases as engine load is increased, which is not reproduced by the current reduced NOx mechanism. HCN and CH were found to be species that bridge CxHy products and N radicals via the reaction CH+N2→HCN+N under high equivalence ratio conditions, and Zeldovich NO formation is suppressed by the formation of HCN, a species in the Fenimore NO formation pathway. The additional species and reactions were also found to influence the prediction of engine-out soot emissions.

A transport equation residual model incorporating refined G-equation and detailed chemical kinetics combustion models has been developed and implemented in the ERC KIVA-3V release2 code for Gasoline Direct Injection (GDI) engine simulations for better predictions of flame propagation. In the transport equation residual model a fictitious species concept is introduced to account for the residual gases in the cylinder, which have a great effect on the laminar flame speed. The residual gases include CO2, H2O and N2 remaining from the previous engine cycle or introduced using EGR. This pseudo species is described by a transport equation. The transport equation residual model differentiates between CO2 and H2O from the previous engine cycle or EGR and that which is from the combustion products of the current engine cycle.

In the present work the three-dimensional KIVA CFD code was used to simulate the combustion process in a HSDI diesel engine. State-of-the-art models, including the KH-RT spray breakup model, the RNG k-ε turbulence model, and a n-heptane reduced chemistry including reduced GRI NOx mechanism were used. The performances of two combustion models, KIVA-CHEMKIN and GAMUT (KIVA-CHEMKIN-G), coupled with 2-step and multi-step phenomenological soot models were compared. The numerical results were compared with available experimental data obtained from an optically accessible HSDI engine and good agreement was obtained. To assess the effects of the in-cylinder flow field on combustion and emissions, off-centered swirl flows were also considered. In these studies, the swirl center was initialized at different positions in the chamber for different cases to simulate the effects of different intake flow arrangements.

Effects of high injection pressure and converging nozzles on combustion and emissions of a multi-cylinder diesel engine were investigated. The engine uses a common-rail injection system that allows a maximum injection pressure of 200 MPa. Various injection pressures were tested to explore the benefits of high injection pressure in achieving low exhaust emissions in diesel engines. Injectors used in this study include conventional straight-hole nozzles and converging nozzles with a K factor of 3. Parametric studies were performed including variations in injection timings, number of injection pulses and EGR levels. It was found that low temperature combustion can be achieved by using high EGR with 1) late single injection or 2) double injection with an early pilot and a late main injection. Investigations revealed that high injection pressures significantly reduced soot emissions with an increase in NOx emissions under conventional injection timing ranges.

Low-temperature combustion (LTC) strategies for diesel engines are of increasing interest because of their potential to significantly reduce particulate matter (PM) and nitrogen oxide (NOx) emissions. LTC with late fuel injection further offers the benefit of combustion phasing control because ignition is closely coupled to the fuel injection event. But with a short ignition-delay, fuel jet mixing processes must be rapid to achieve adequate premixing before ignition. In the current study, mixing and pollutant formation of late-injection LTC are studied in a single-cylinder, direct-injection, optically accessible heavy-duty diesel engine using three laser-based imaging diagnostics. Simultaneous planar laser-induced fluorescence of the hydroxyl radical (OH) and combined formaldehyde (H2CO) and polycyclic aromatic hydrocarbons (PAH) are compared with vapor-fuel concentration measurements from a non-combusting condition.

The lift-off length plays a significant role in spray combustion as it influences the air entrainment upstream of the lift-off location and hence the soot formation. Accurate prediction of lift-off length thus becomes a prerequisite for accurate soot prediction in lifted flames. In the present study, KIVA-3v coupled with CHEMKIN, as developed at the Engine Research Center (ERC), is used as the CFD model. Experimental data from the Sandia National Labs. is used for validating the model predictions of n-heptane lift-off lengths and soot formation details in a constant volume combustion chamber. It is seen that the model predictions, in terms of lift-off length and soot mass, agree well with the experimental results for low ambient density (14.8 kg/m3) cases with different EGR rates (21% O2 - 8% O2). However, for high density cases (30 kg/m3) with different EGR rates (15% O2 - 8% O2) disagreements were found.

Particulate matters, nitrogen oxides, and carbon monoxides emissions from large utility generators using diesel/biodiesel blends were measured. Stack measurements were performed on-site in a number of power plants by following the standard procedure of US EPA. The test engines were chosen to represent typical diesel engines used for electricity generation in the state. Tests were performed using the regular diesel fuel (B0), 10%, 20% and 100% biodiesel blends (B10, B20, B100). Test results showed that particulate matters and carbon monoxides decreased significantly as biodiesel content increases, whereas nitrogen oxides increased. Test results are consistent with other studies using mobile engines in the literature. Note that arbitrary changes in fuel or engine operating conditions are prohibited in power generation industry. Results of this study have been used by the state government to allow the use of biodiesel blends in stationary generators.

Homogeneous Charge Compression Ignition (HCCI) combustion is being considered as a practical solution for diesel engines due to its high efficiency and low NOx and PM emissions. However, for diesel HCCI operation, there are still several problems that need to be solved. One is the spay-wall impingement issue associated with early injection, and a further problem is the extension of HCCI operation from low load to higher engine loads. In this study, a combination of Adaptive Injection Strategies (AIS) and a Two-Stage Combustion (TSC) strategy are proposed to solve the aforementioned problems. A multi-dimensional Computational Fluid Dynamics (CFD) code with detailed chemistry, the KIVA-CHEMKIN-GA code, was employed in this study, where Genetic Algorithms (GA) were used to optimize heavy-duty diesel engine operating parameters. The TSC concept was applied to optimize the combustion process at high speed (1737 rev/min) and medium load (57% load).

Stoichiometric combustion could enable a three-way catalyst to be used for treating NOx emissions of diesel engines, which is one of the most difficult species for diesel engines to meet future emission regulations. Previous study by Lee et al. [1] showed that diesel engines can operate with stoichiometric combustion successfully with only a minor impact on fuel consumption. Low NOx emission levels were another advantage of stoichiometric operation according to that study. In this study, the characteristics of stoichiometric diesel combustion were evaluated experimentally to improve fuel economy as well as exhaust emissions The effects of fuel injection pressure, boost pressure, swirl, intake air temperature, combustion regime (injection timing), and engine load (fuel mass injected) were assessed under stoichiometric conditions.

Numerical models were used to study the effects of dimethyl ether (DME) on the operation of a compression-ignition engine fueled with premixed natural gas. The models used multi-dimensional engine CFD coupled with detailed chemical kinetics. Combustion characteristics of various compositions of the natural gas and DME mixture were simulated. Results showed that combustion phasing, nitrogen oxides emissions, and effects of fuel compositions on engine operating limits were well predicted. Chemical kinetics analysis indicated that ignition was achieved by DME oxidation, which, in turn, induced natural gas combustion. It was found that low temperature heat release became more significant as DME concentration increased. For an appropriate amount of DME in the mixture, the stable engine operating range became narrower as natural gas concentration increased. The model also captured the low temperature combustion features of the present engine with low nitrogen oxides emissions.

High-speed video imaging in a swirl-supported (Rs = 1.7), direct-injection heavy-duty diesel engine operated with moderate-to-high EGR rates reveals a distinct correlation between the spatial distribution of luminous soot and mean flow vorticity in the horizontal plane. The temporal behavior of the experimental images, as well as the results of multi-dimensional numerical simulations, show that this soot-vorticity correlation is caused by the presence of a greater amount of soot on the windward side of the jet. The simulations indicate that while flow swirl can influence pre-ignition mixing processes as well as post-combustion soot oxidation processes, interactions between the swirl and the heat release can also influence mixing processes. Without swirl, combustion-generated gas flows influence mixing on both sides of the jet equally. In the presence of swirl, the heat release occurs on the leeward side of the fuel sprays.

Parametric tests using various EGR amounts, boost intake pressures, fueling rates, intake valve closings (IVC), injection pressures, and start-of-injection timings were executed to explore the limitations and potential of an intake valve actuation system on a heavy-duty diesel engine. At high-speed, intermediate load (56%) operation, constant airflow and no EGR, the use of late intake valve closing enabled a 70% NOx reduction while maintaining PM levels. Through an investigation using low load operation, late IVC, and reduced intake pressure, 2010 not-to-exceed NOx and PM emissions (0.25 g/kW-hr NOx, 0.02 g/kW-hr PM) were achieved with 40% EGR. At medium load, constant air flow, and early SOI, it was found that the NOx, HC and BSFC levels at a late IVC with 30%EGR were comparable to those with the stock camshaft IVC timing of 143°BTDC with 40%EGR. In comparison, the CO and PM levels decreased by nearly 70% with the use of late IVC timing and less EGR.

Sustainable PCI combustion was achieved in a light-duty diesel engine through the installation of a 120° spray angle nozzle and modeling-generated piston bowl geometry developed for compatibility with early start-of-injection timings. Experimental studies were conducted to determine favorable settings for boost pressure, SOI timing, and EGR rate at 2000 rev/min, 5 bar BMEP. An optimal SOI timing was discovered at 43° BTDC where soot and NOx emissions were reduced 89% and 86%, respectively. A 10% increase in fuel consumption was attributed to increased HC and CO emissions as well as non-optimal combustion phasing. Combustion noise was sufficiently attenuated through the use of high EGR rates. The maximum attainable load for PCI combustion was limited by the engine's peak cylinder pressure and cylinder pressure rise rate constraints.

Optimizations were performed on a single-cylinder heavy-duty Caterpillar SCOTE 3401E engine for NOx, PM and BSFC reductions. The engine was equipped with a Caterpillar 300B HEUI fuel injection system capable of up to four injections with timings from 90 BTDC to 90 ATDC. The engine was operated at a medium load (57%), high speed (1737 rev/min) operation point. A micro-genetic algorithm was utilized to optimize a hybrid, double-injection strategy, which incorporated an early, premixed pilot injection with a late main injection. The fuel injection parameters, intake boost pressure, and EGR were considered in the optimization. The optimization produced a parameter set that met the 2007 and 2010 PM emissions mandate of 0.0134 g/kW-hr, and was within the 1.5x not to exceed NOx + HC mandate of 2.694 g/kW-hr. Following the optimization exercise, further parametric interaction studies were performed to reveal the underlying interactions and phenomena.

The effect of spray targeting on exhaust emissions, especially soot and carbon monoxide (CO) formation, were investigated in a single-cylinder, high-speed, direct-injection (HSDI) diesel engine. The spray targeting was examined by sweeping the start-of-injection (SOI) timing with several nozzles which had different spray angles ranging from 50° to 154°. The tests were organized to monitor the emissions in Premixed Charge Compression Ignition (PCCI) combustion by introducing high levels of EGR (55%) with a relatively low compression ratio (16.0) and an open-crater type piston bowl. The study showed that there were optimum targeting spots on the piston bowl with respect to soot and CO formation, while nitric oxide (NOx) formation was not affected by the targeting. The soot and CO production were minimized when the spray was targeted at the edge of the piston bowl near the squish zone, regardless of the spray angle.

Combustion in an HSDI diesel engine using different injectors to realize low emissions is modeled using detailed chemical kinetics in this study. Emission characteristics of the engine are investigated using injectors that have different included spray angles, ranging from 50 to 130 degrees. The engine was operated under PCCI conditions featuring early injection times, high EGR levels and high intake temperatures. The Representative Interactive Flamelet (RIF) model was used with the KIVA code for combustion and emission modeling. Modeling results show that spray targeting plays an important role in determining the in-cylinder mixture distributions, which in turn affect the resulting pollutant emissions. High soot emissions are observed for injection conditions that result in locally fuel rich regions due to spray impingement normal to the piston surface.