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Diesel soot suppression effects of catalytic fuel additives for a range of fuels with different properties were investigated with calcium naphthenate. A single cylinder DI diesel engine and a thermobalance were used to determine the soot reduction and its mechanism for seven kinds of fuels. Experimental results showed that the catalytic effect of the fuel additive was different for the different fuels, and could be described by a parameter considering cetane number and kinematic viscosity. The fuel additives reduced soot more effectively for fuels with higher cetane number and lower kinematic viscosity. This result was explained by soot oxidation characteristics for the different fuels. Oxidation of soot with the metallic additive proceeds in two stages: stage I, a very rapid oxidation stage; and stage II, a following slow or ordinary oxidation stage.

This research investigates the influences of the injection timing, injection pressure, and compression ratio on the combustion and exhaust emissions in a single cylinder 1.0 L DI diesel engine operating with ultra-high EGR. Longer ignition delays due to either advancing or retarding the injection timing reduced the smoke emissions, but advancing the injection timing has the advantages of maintaining the thermal efficiency and preventing misfiring. Smokeless combustion is realized with an intake oxygen content of only 9-10% regardless of the injection pressure. Reduction in the compression ratio is effective to reduce the in-cylinder temperature and increase the ignition delay as well as to expand the smokeless combustion range in terms of EGR and IMEP. However, the thermal efficiency deteriorates with excessively low compression ratios.

Soot emissions in the combustion process of diesel engines are greatly harmful to the environment and human health. Consequently, there is large interest and great efforts in decreasing soot emission from diesel engines to meet the increasingly stringent emission standards. The mechanisms of soot formation and oxidation so far have not been well understood. Laser induced incandescence (LII) is particularly suited to measure the instantaneous spatial distribution of the soot volume concentration, which can offer much needed detailed information of soot distribution for better understanding of soot formation and oxidation. In this paper, a two-color laser induced incandescence (2C-LII) technique was implemented for measuring absolute soot volume fraction in a laminar diesel fuel diffusion flame.

Urea Selective Catalytic Reduction (SCR) has been proven to significantly reduce NOx emissions from diesel engines. The thermal decomposition of urea, which forms the ammonia as the reactant, has a crucial effect on the performance and durability of the NOx-SCR system. The incomplete thermal decomposition of urea not only reduces the NOx conversion ratio and increases the ammonia slip, but also leads to deposit formation on the catalyst surface, which will block the pore and the active sites of the catalyst and then decreases the durability of the SCR systems. In this paper, the urea thermolysis was measured using the Thermal Gravimetric Analysis (TGA) and Fourier Transform Infrared Spectroscopy (FTIR). Then, the performance of the SCR systems under different injection parameters of the Urea-water solution was investigated on a diesel engine test bench. Finally, the deposits on the catalyst were also analyzed using TGA and FTIR.

Beijing will implement the 4th stage emission regulations (equivalent to Euro IV) in 2008 ahead of other provinces or cites in China. Beijing Environmental Protection Bureau (EPB) organized petroleum corporations, automobile and engine manufactories as well as research institutes to test the adaptability of the fuels from Chinese refineries to the modern vehicles or engines on the road running conditions in China. In this paper, the effects of diesel fuel quality on combustion and emission of a Euro IV heavy-duty diesel engine as one part of the program were studied to provide technical data to stipulate the feasible diesel fuel standard, which should guarantee modern vehicles or engines to meet the 4th stage regulations. Eight kinds of diesel fuels with different properties, such as cetane number, distillation temperature (T90) and sulfur content, were tested on a Euro IV Cummins heavy-duty diesel engine with urea SCR after-treatment.

This paper investigates the combined effect of EGR and emulsified fuels on engine performance. The influence of intake air temperature (25∼86°C) on engine performance was examined prior to uncooled EGR experiments. Compared with gas oil, emulsified fuel gave simultaneous improvements in NOx concentration, smoke density, and specific fuel consumption (BSFC) over the tested range. The effect of EGR on engine performance were investigated with various water to fuel ratios at two load conditions (BMEP=0.52MPa and 0.26MPa). It was confirmed that at 11% EGR with the emulsified fuel at the rated output resulted in a significant reduction in NOx concentration without worsening smoke density and BSFC.

In a DI diesel engine, THC emissions increase significantly with lower compression ratios, a low coolant temperature, or during the transient state. During the transient after a load increase, THC emissions are increased significantly to very high concentrations from just after the start of the load increase until around the 10th cycle, then rapidly decreased until the 20th cycle, before gradually decreasing to a steady state value after 1000 cycles. In the fully-warmed steady state operation with a compression ratio of 16 and diesel fuel, THC is reasonably low, but THC increases with lower coolant temperatures or during the transient period just after increasing the load. This THC increase is due to the formation of over-lean mixture with the longer ignition delay and also due to the fuel adhering to the combustion chamber walls. A low distillation temperature fuel such as normal heptane can eliminate the THC increase.

On the basis of modular pulse converter (MPC) exhaust system the authors present a new swirl exhaust system. Structural parameters on the swirl exhaust system and MPC system for N8160ZC diesel engine were calculated by a mathematical optimum method, and the two systems were tested under the same engine operation for comparison. Experimental results show that the swirl exhaust system has a better engine performance under most of the operating conditions than MPC system, but worse under the low-speed and part-load conditions. In order to understand the mechanism of this swirl exhaust system well, a three-dimensional particle dynamic analyzer (3D-PDA) was utilized to measure the steady turbulent airflow in a swirl three-branched model. The computational fluid dynamics (CFD) code KIVA was modified to simulate the flows. Computational results are in good agreement with measuring ones and reveal the swirl flow behavior in the junction.

The thermal cracking and polyaromatic hydrocarbon (PAH) formation processes of dimethyl ether (DME), ethanol, and ethane were investigated with chemical kinetics to determine the soot formation mechanism of oxygenated fuels. The modeling analyzed three processes, an isothermal constant pressure condition, a temperature rising condition under a constant pressure, and an unsteady condition approximating diesel combustion. With the same mole number of oxygen atoms, the DME rich mixtures form much carbon monoxide and methane and very little non-methane HC and PAH, in comparison with ethanol or ethane mixtures. This suggests that the existence of the C-C bond promotes the formation of PAH and soot.

Time resolved changes in unburned hydrocarbon emissions and their components were investigated in a DI diesel engine with a specially developed gas sampling system and gas chromatography. The tested transient operations include starting and increasing loads. At start-up with high equivalence ratios the total hydrocarbon (THC) at first increased, and after a maximum gradually decreased to reach a steady state value. Reducing the equivalence ratio of the high fueling at start-up and shortening the high fueling duration are effective to reduce THC emissions as long as sufficient startability is maintained. Lower hydrocarbons, mainly C1-C8, were the dominant components of the THC and mainly determined the THC behavior in the transient operations while the proportion of hydrocarbon (HC) components did not significantly change. The unregulated toxic substances, 1,3 butadiene and benzene were detected in small quantities.

Smokeless and ultra low NOx combustion without knocking in a dual-fuel diesel engine with induced LPG as the main fuel was established with a uniquely developed piston cavity divided by a lip in the sidewall. A small quantity of diesel fuel was directly injected at early compression stroke into the lower part of the cavity as an ignition source for this confined area, and this suppressed explosively rapid combustion just after ignition and spark-knock like combustion at later stage. A combination of the divided cavity, EGR, and intake air throttling was effective to simultaneously eliminate knocking, and reduce THC and NOx significantly.

The fundamental parameters related to engine combustion and performances, such as, heating value, theoretical air-fuel ratio, adiabatic flame temperature, carbon dioxide (CO2), and nitric oxide (NO) emissions, specific heat and engine thermal efficiency were investigated with computations for a wide range of oxygenated fuels. The computed results showed that almost all of the above combustion-related parameters are closely related to oxygen content in the fuels regardless of the kinds or chemical structures of oxygenated fuels. An interesting finding was that with the increase in oxygen content in the fuels NO emission decreased linearly, and the engine thermal efficiency was almost unchanged below oxygen content of 30 wt-% but gradually decreased above 30 wt-%.

Direct injection of various ignition suppressors, including water, methanol, ethanol, 1-propanol, hydrogen, and methane, was implemented to control ignition timing and expand the operating range in an HCCI engine with induced DME as the main fuel. Ultra-low NOx and smoke-less combustion was realized over a wide operating range. The reaction suppressors reduced the rate of low-temperature oxidation and consequently delayed the onset of high-temperature oxidation. Analysis of the chemical kinetics showed a reduction of OH radical in the premixed charge with the suppressors. Among the ignition suppressors, alcohols had a greater impact on OH radical reduction resulting in stronger ignition suppression. Although water injection caused a greater lowering of the temperature, which also suppressed ignition, the strong chemical effect of radical reduction with methanol injection resulted in the larger impact on suppression of oxidation reaction rates.

This investigation reports diesel engine performance of water-in-gas oil emulsified fuel and gas oil at compression ratios of 13.6, 15.6, and 17.0. It was confirmed that without worsening the specific fuel consumption, low compression ratios with emulsified fuel operation result in significant reductions in NOx concentration, reduced maximum combustion pressure, and decreased smoke density when compared with the 17.0 compression ratio for gas oil operation.

A Homogeneous charge induced ignition (HCII) combustion, realized by in-cylinder fuel blending of gasoline and diesel fuel, was developed and carefully optimized, both on a single cylinder and a multi-cylinder light-duty diesel engines, for high thermal efficiency and near zero emissions in a wide engine-operation range up to IMEP of 1 MPa. The effects of mixing and chemical parameters of HCII combustion, which can be controlled by production-viable hard-ware using conventional gasoline and diesel fuel, include injection timing of diesel fuel, injection rate pattern of diesel fuel (such as split injection), the gasoline/diesel ratio, boost pressure and exhaust gas recirculation (EGR). Based on a single cylinder engine, the experimental result shows that the interaction of the mentioned control parameters plays decisive role in determination of exhaust emissions and thermal efficiency.

Mixture formation processes of intermittent gas jets were visualized and quantified with high accuracy by a uniquely developed LIF technique (LIFA). Mixture strength inside gas jets was quantified by the fluorescence of iodine in the ambient gas excited by the sheet light of a Nd:YAG laser Two dimensional images of intermittent gas jets of various velocities were continuously recorded with VTR and quantified with high accuracy. The optimum conditions for measurements and accuracy with the LIFA technique were investigated. At the optimum setting of the initial iodine concentration in the ambient gas, accuracies better than 95% were obtained for the ambient gas entrainment ratio or jet concentration. The experimental results show that considerable amounts of ambient gas entrain just under the umbrella-like profile at the top of the jet. The mean jet concentration decreased with decreased nozzle diameter (D), and time elapsed after injection (Δt).

The effects of several fuel property variables on the emissions from a D.I. diesel engine were individually analyzed. The results showed that the smoke and dry soot increased with increased kinematic viscosity, shorter ignition lag, and higher aromatic content, especially at high equivalence ratios. Over the whole range of equivalence ratios, SOF depended on and increased with only ignition lag. The NOx improved slightly with increased kinematic viscosity, higher ignitability, and decreased aromatic content. The unburnt HC also improved with decreased kinematic viscosity and higher ignitability. The distribution shape of distillation curves had little influence on the emissions.

A new concept DISC engine equipped with a two-stage injection system was developed. The engine was modified from a single cylinder DI diesel engine with large cylinder diameter (135mm). Combustion characteristics and exhaust emissions with regular gasoline were examined, and the experiments were also made with gasoline-diesel fuel blends with higher boiling temperatures and lower octane numbers. To realize stratified mixture distribution in combustion chamber flexibly, the fuel was injected in two-stages: the first stage was before the compression stroke to create a uniform premixed lean mixture and the second stage was at the end of the compression stroke to maintain stable ignition and faster combustion. In this paper, the effect of the two-stage injection on combustion and exhaust emissions were analyzed under several operating conditions.

The effect of direct water injection into the combustion chamber on NOx reduction in an IDI diesel engine was investigated. The temperature distribution in the swirl chamber was analyzed quantitatively with high speed photography and the two color method. Direct water injection into a swirl chamber prior to fuel injection reduced NOx emission significantly over a wide output range without sacrifice of BSFC. Other emissions were almost unchanged or slightly decreased with water injection. Water injection reduced the flame temperature at the center of the swirl chamber, while the mean gas temperature in the cylinder and the rate of heat release changed little.

Diesel combustion and exhaust gas emissions under transient operation (when fuel amounts abruptly increased) were investigated under a wide range of operating conditions with a newly developed gas sampling system. The relation between gas emissions and piston wall temperatures was also investigated. The results indicated that after the start of acceleration NOx, THC and smoke showed transient behaviors before reaching the steady state condition. Of the three gases, THC was most affected by piston wall temperature; its concentration decreased as the wall temperature increased throughout the acceleration except immediately after the start of acceleration. The number of cycles, at which gas concentrations reach the steady-state value after the start of acceleration, were about 1.2 times the cycle constant of the piston wall temperature for THC, and 2.3 times for smoke.