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Light naphtha, which exhibits two-stage ignition, was induced from the intake manifold for ignition enhancement and a low ignitability fuel or water, which does not exhibit low temperature oxidation, was directly injected early in the compression stroke for ignition suppression in an HCCI engine. Their quantitative balance was flexibly controlled to optimize ignition timing according to operating condition. Ultra-low NOx and smokeless combustion without knocking or misfiring was realized over a wide operating range. Alcohols inhibit low temperature oxidation more strongly than other oxygenated or unoxygenated hydrocarbons, water, and hydrogen. Chemical kinetic modeling for methanol showed a reduction of OH radical concentration before the onset of low temperature oxidation, and this may be the main mechanism by which alcohols inhibit low temperature oxidation.

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.

Combustion and exhaust gas emissions of alcohol and vegetable oil blends including a 20% ethanol + 40% 1-butanol + 40% vegetable oil blend and a 50% 1-butanol + 50% vegetable oil blend were examined in a single cylinder, four-stroke cycle, 0.83L direct injection diesel engine, with a supercharger and a common rail fuel injection system. A 50% diesel oil + 50% vegetable oil blend and regular unblended diesel fuel were used as reference fuels. The boost pressure was kept constant at 160 kPa (absolute pressure), and the cooled low pressure loop EGR was realized by mixing with a part of the exhaust gas. Pilot injection is effective to suppress rapid combustion due to the lower ignitability of the alcohol and vegetable oil blends. The effects of reductions in the intake oxygen concentration with cooled EGR and changes in the fuel injection pressure were investigated for the blended fuels.

The combustion characteristics in a partially premixed charge compression ignition (PCCI) engine with n-hexane were compared with ordinary diesel fuel to evaluate combustion improvements with lower distillation-temperature fuels. In the PCCI engine, a lean mixture was formed reasonably with early stage injection and the additional fuel was supplied with a second stage fuel injection after ignition. With n-hexane, thermal efficiency improved while simultaneously maintaining low NOx and smokeless combustion. A CFD analysis simulated the mixture formation processes and showed that the uniformity of the mixture with the first stage injection improves with lower distillation-temperature fuels.

Cycle-to-cycle changes in diesel exhaust gas emissions were investigated under two transient operation patterns: One, “an interval step decreasing and increasing load”, where the fuel amount is rapidly decreased from high to low loads, and after an interval, Δtint the fuel amount is abruptly returned to the initial level. The other is “a ramp increasing load”, where the fuel amount is increased gradually. Except just after the step increase in fuel amounts, the THC emissions were almost completely determined by the piston wall temperature and fuel amount. However, the THC concentrations immediately after the step increase in fuel amounts were much higher than the value of the corresponding steady state operation with the same piston wall temperature. This overshoot concentration, ΔTHC, was almost constant at different intervals, Δtint and it can be suppressed by ramp increased loading.

Changes in exhaust gas emissions during starting in a DI diesel engine were investigated. The THC after starting increased until around the 50th cycle when the fuel deposited on the combustion chamber showed the maximum, and THC then decreased to reach a steady value after about 1000 cycles when the piston wall temperature became constant. The NOx showed an initial higher peak just after starting, and increased to a steady value after about 1000 cycles. Exhaust odor had a strong correlation with THC, and at the early stage odor was stronger than would be expected from the THC concentration. The THC increased with increased fuel injection amounts, decreased cranking speeds, and fuels with higher viscosity, higher 90% distillation temperature, and lower ignitability.

The dependence of ultra-high EGR low temperature diesel combustion on fuel properties including cetane number and distillation temperature was investigated with a single-cylinder, naturally aspirated, 1.0 L, common rail DI diesel engine. Decreasing cetane number in fuels significantly reduces smoke emission due to an extension in ignition delay and the subsequent improvement in mixture formation. Smokeless combustion, ultra-low NOx, and efficient operating range with regard to EGR and IMEP are significantly extended by decreasing fuel cetane number. Changes in fuel distillation temperature do not result in significant differences in smoke emission and thermal efficiency for ultra-high EGR operation, and smokeless operation is established even with higher distillation temperature fuels as long as fuel cetane number is sufficiently low.

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.

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.

To reduce NOx emissions from diesel engines, the urea-SCR (selective catalytic reduction) system has been introduced commercially. In urea-SCR, the freezing point of the urea aqueous solution, the deoxidizer, is −11°C, and the handling of the deoxidizer under cold weather conditions is a problem. Further, the ammonia escape from the catalyst and the generation of N2O emissions are also problems. To overcome these disadvantages of the urea-SCR system, the addition of a hydrocarbon deoxidizer has attracted attention. In this paper, a micro-reactor SCR system was developed and attached to the exhaust pipe of a single cylinder diesel engine. With the micro-reactor, the catalyst temperature, quantity of deoxidizer, and the space velocity can be controlled, and it is possible to use it with gas and liquid phase deoxidizers. The catalyst used in the tests reported here is Ag(1wt%)-γAl2O3.

The influence of aromatic content in fuels on the soot and NOx emissions from a diesel engine was analyzed under controlled ignition lags with spark-assisted operation. Monocyclic aromatic hydrocarbons and n-hexane mixtures were used as fuels, and the aromatic content was varied from 0 to 75 v-%. The experiments showed that, at the same equivalence ratio and regardless of the molecular structure of the fuel, the soot concentration in the exhaust gas could be described by a linear-combination function with two variables representing the ignition lag and C/H atom-ratio of the fuels. For unchanged ignition lags, the soot emissions increased linearly with increased C/H atom-ratios, which are controlled by the aromatic content. The degree of increase in soot emissions with increasing C/H atom-ratio decreased with decreasing equivalence ratios. The NOx emission increased slightly with increases in the C/H atom-ratio and ignition lag.

Premixed diesel combustion was performed and various characteristics examined with fuel injection timing near top dead center (TDC). A lean and uniform fuel-air mixture was found to during 25° C.A. with a narrow injection angle (27.5° with respect to horizontal), shallow dish combustion chamber, and low cetane number fuel (CN=19). These conditions enabled low NOx combustion in no exhaust gas re-circulation (EGR), despite fuel injection timing around 25° BTDC. Furthermore, HC emissions were lower than with premixed diesel combustion of the early injection type. Because fuel injection timing was near TDC, the volume of the mixture dispersed to a squish area was decreased. This combustion mode was also achieved with a high-cetane fuel (conventional diesel fuel) and high EGR rate conditions. However, in this case, it was difficult to adjust the ignition timing near top dead center. This combustion system also showed good performance in conventional diesel combustion mode.

Unregulated emissions from a DI diesel engine with ultra-high EGR low temperature combustion were analyzed using Fourier transform infrared (FTIR) spectroscopy and the reduction characteristics of both regulated and unregulated emissions by two exhaust catalysts were investigated. With ultra-high EGR suppressing the in-cylinder soot and Nox formation as well as with the exhaust catalysts removing the engine-out THC and CO emissions, clean diesel operation in terms of ultra-low regulated emissions (Nox, PM, THC, and CO) is established in an operating range up to 50% load. To realize smokeless low temperature combustion at higher loads, EGR has to be increased to a rate with the overall (average) excess air ratio less than the stoichiometric ratio.

Characteristics of diesel combustion with low cetane number fuels with similar distillation temperatures to ordinary diesel fuel, including fuels with cetane number 32 and 39 (LC32, LC39), and a blend of n-cetane (n-hexadecane) and iso-cetane (2, 2, 4, 4, 6, 8, 8-heptamethylnonane) with cetane number 32 (CN32), were investigated. The effects of cooled exhaust gas recirculation (EGR) and pilot injection on characteristics of combustion and exhaust gas emissions with these fuels were examined in a naturally aspirated, single cylinder, diesel engine equipped with a common-rail fuel injection system. Even with the low cetane number fuels, quiet combustion with low levels of exhaust gas emissions comparable to ordinary diesel fuel was established by suitable control of intake oxygen levels and pilot injections.

To find more effective lean mixture preparation methods for smokeless and low NOx combustion, a numerical study of the effects of in-cylinder flow field before injection on mixture formation in a premixed compression ignition engine was conducted. Premixed compression ignition combustion is a very attractive method to reduce both NOx and soot emissions, but it still has some problems, such as high HC and CO emissions. In case of early direct injection, it is important to avoid wall wetting by spray impingement, which can cause higher HC and CO emissions. Since it is not easy to examine the effects of initial flow and injection parameters on mixture formation over the wide range by practical engine tests, a computer program named “GTT (Generalized Tank and Tube)” code was used to simulate the in-cylinder phenomena before autoignition.

HCCI (Homogeneous Charge Compression Ignition) combustion results in very low NOx emissions, however, it is not without problems. One of them is that the heavy load operation range is limited by knock, due to an exceptionally high heat release rate. Knock increases the heat loss to the cylinder walls and piston, reducing thermal efficiency. To help solve these problems, direct (in-cylinder) water injection has been suggested to lower the local temperatures that seem to cause knock in HCCI. Water injection was adapted in an HCCI engine fueled with DME and Propane. Results showed that the indicated thermal efficiency was improved by about 2% (λ = 3.0, NA), and the operation range was expanded from 460kPa to 700kPa (NA) maintaining a low NOx level.

The HCCI engine offers the potential of low NOx emissions combined with diesel engine like high efficiency, however HCCI operation is restricted to low engine speeds and torques constrained by narrow noise (HCCI knocking) and misfiring limits. Gasoline like fuel vaporizes and mixes with air, but the mixture may auto-ignite at the same time, leading to heavy HCCI knocking. Retarding the CA50 (the crank angle of the 50% burn) is well known as a method to slow the maximum pressure rise rate and reduce HCCI knocking. The CA50 can be controlled by the fuel composition, for example, di-methyl ether (DME), which is easily synthesized from natural gas, has strong low temperature heat release (LTHR) characteristics and ethanol generates strong LTHR inhibitor effects. The utilization of DME-ethanol binary blended fuels has the potential to broaden the HCCI engine load-speed range.

To determine the engine noise reduction methods, an engine noise research was conducted experimentally with a PCCI diesel engine. The engine employed in the experiments was a supercharged, single-cylinder DI diesel engine with a high pressure common rail fuel injection system. The engine noise was sampled by two microphones and the sampled engine noise was averaged and analyzed by an FFT sound analyzer. The engine was equipped with a pressure transducer and the combustion noise was calculated from the power spectrum of the FFT analysis of the in-cylinder pressure wave form and the cross power spectrum of the sound pressure of the engine noise. It is well known that the maximum pressure rise rate is the main parameter related to the engine noise. The PCCI engine was operated at a 1.0 MPa/°CA maximum pressure rise rate to eliminate the effects of the maximum pressure rise rate, and parameters which had the dominant effect on engine noise and combustion noise were determined.

Diesel particulate filters (DPF) are widely used in diesel engines, and forced regeneration is necessary to remove particulate matter (PM) accumulating on the DPF. This may be achieved with fuel injected after the main combustion is complete, the socalled “post fuel injection”, and supplied to the diesel oxidation catalyst (DOC) upstream of the DPF. This increases the exhaust gas temperature in the DOC and the DPF is regenerated with the high temperature gas flow. In most cases, the post fuel injection takes place at 30-90CA ATDC, and fuel may impinge on and adhere to the cylinder liner wall in some cases. Buddie and Pischinger [1] have reported a lubricant oil dilution with the post fuel injection by engine tests and simulations, and adhering fuel is a cause of worsening fuel consumption. In this paper, the impingement and adhesion of post diesel fuel injections on the cylinder liner was investigated by an optical method with a high pressure constant volume chamber (ϕ110mm, 883cm3).

Port injection of ethanol addition as an ignition inhibitor was implemented to control ignition timing and expand the operating range in DME fueled HCCI combustion. The ethanol reduced the rate of low-temperature oxidation and consequently delayed the onset of the high-temperature reaction with ultra-low NOx over a wide operating range. Along with the ethanol addition, changes in intake temperature, overall equivalence ratio, and engine speed are investigated and shown to be effective in HCCI combustion control and to enable an extension of operation range. A chemical reaction analysis was performed to elucidate details of the ignition inhibition on low-temperature oxidation of DME-HCCI combustion.