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When fuel is vaporized and mixed well with air in the cylinder of premixed diesel engines, the mixture auto-ignites in one burst resulting in strong combustion noise, and combustion noise reduction is necessary to achieve high load premixed diesel engine operation. In this paper, an engine noise analysis was conducted by engine tests and simulations. 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 data from the cross power spectrum of the sound pressure of the engine noise.

Premixed diesel combustion is effective for high thermal efficiency and reductions of NOx and PM emissions, but a reduction of combustion noise is necessary for medium-high load engine operation. The control of the fuel injection has become more accurate because of the technical progress of the common rail fuel injection system, and the target heat release shape, calculated by computation, can be achieved by control of EGR, boosting, fuel injection timing, and injection quantity of multiple fuel injections. In this paper, the reduction of premixed diesel combustion noise maintaining high thermal efficiency has been investigated by the control of injection timings and heating values of multiple fuel injections. There are two aspects of the combustion noise reduction by multiple fuel injections. One is the reduction of the maximum rate of pressure rise in each combustion cycle, and the other is noise reduction effects by the noise cancelling spike (NCS) combustion.

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.

Reductions in combustion noise are necessary in high load diesel engine operation and multiple fuel injections can achieve this with the resulting reductions in the maximum rate of pressure rise. In 2014, Dr. Fuyuto reported the phenomenon that the combustion noise produced in the first combustion can be reduced by the combustion noise of the second fuel injection, and this has been named “Noise Cancelling Spike Combustion (NCS combustion)”. To investigate more details of NCS combustion, the effects of timings and heating values of the first and second heat releases on the reduction of overall combustion noise are investigated in this paper. The engine employed in the research here is a supercharged, single cylinder DI diesel engine with a high pressure common rail fuel injection system.

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.

Dual fuel combustion with premixed ethanol as the main fuel and direct injection of diesel fuel as an ignition source poses problems including large unburned emissions and excessively rapid combustion. In this report the influence of compression ratios, injection timings of diesel fuel, and intake oxygen concentrations was systematically investigated in a modern diesel engine. The combustion process was classified into three stages: the first rapid combustion of diesel fuel and the ethanol mixture entrained into the diesel fuel spray; the second mild combustion with flame propagation of the ethanol mixture; and the third rapid combustion with auto-ignition of the unburned ethanol mixture without knocking. The third stage combustion occurs occasionally at several operating conditions and has been termed as PREMIER (premixed mixture ignition in the end-gas region) combustion.

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.

For better understanding of diesel emissions in real world, the effects of driving conditions and fuel properties on diesel emissions were studied. A diesel engine system that is compliant to the Japanese New Short Term Regulation (J-2003 regulation) was used in this study. Major technologies for emission reduction were a common-rail high-pressure fuel injection equipment system, a cooled exhaust gas recirculation (EGR) system and a diesel oxidation catalyst (DOC). Various driving modes with a wide range of average vehicle speeds and accelerations were selected, including US FTP, US Highway, Japanese JC08, Japanese JE05, Tokyo Metropolitan Government #2, #5 and #8. Several kinds of test fuels of which characteristics were drastically changed in distillation range, aromatics content and sulfur content were used. A test fuel that complies with the Category-4 Specification of the World-Wide Fuel Charter (WWFC) was included.

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.

Forced ignition with glow plugs has great potential for the utilization of alcohol fuels in diesel engines. However, the installation of glow plugs may cause misfiring or knocking in parts of the operating range. This paper presents an analysis of the factors influencing the ignition characteristics of ethanol in a glow plug-assisted diesel engine; these factors may be classified into two categories: the factors related to the temperature history of the drop lets before contact with the glow plug, and those related to the probability of contact. By optimizing these factors, the combustion difficulties were successfully eliminated over the whole operating range, and engine performance comparable with conventional diesel operation was achieved.

The objective of this program was to improve the HCCI combustion process on a single-cylinder VCR engine by calibrating engine and HCCI operation specific factors such as EGR flow rates, intake air pressure, intake air temperature, compression ratio, etc. Due to the large number of factors to be investigated, a statistical design of experiments method (DoE) was utilized in order to reduce the number of test combinations in the calibration test matrix and, thus, the duration of the engine calibration task. Upon completion of the HCCI engine calibration, the engine was operated through a steady-state test matrix representing vehicle certification test cycles. Weighting factors for each of the test points were applied to estimate the engine performance and emissions in respect to certification requirements.

The control of fuel ignition timing and suppression of rapid combustion in a premixed charge compression ignition (PCCI) engine was attempted with direct in-cylinder injection of water as a reaction suppressor. The water injection significantly reduced the heat release at low temperature oxidation, which suppressed the increase in charge temperature after the low temperature oxidation and the rapid combustion caused by the high temperature oxidation. The possible engine operating range with ultra low NOx and smokeless combustion was extended to a higher load range with the water injection. Rapid combustion was suppressed by reductions in the maximum in-cylinder gas temperature due to water injection while the combustion efficiency suffered. Therefore, the maximum charge temperature needs to be controlled within an extremely limited range to maintain a satisfactory compromise between mild combustion and high combustion efficiency.