Low Compression Ratio Diesel Engine Research Articles

A novel strategy of extremely delayed intake valve opening to improve the cold-start characteristics of a low compression ratio diesel engine

Combined in-cylinder and after-treatment emission control methods are generally adopted to meet the current stringent emission targets for diesel engines. It is well established that reducing the geometric compression ratio (CR) results in a simultaneous reduction in the oxides of nitrogen (NOx) and soot emissions in diesel engines. However, poor cold-start characteristics prevent extensive use of low compression ratio (LCR) diesel engines for automotive applications. In the present work, a novel extremely delayed intake valve opening (IVO) strategy is proposed to improve the cold-start characteristics of a light-duty LCR diesel engine. A commercial one-dimensional gas-exchange model was used to optimize the intake valve open and close timings. The results corresponding to a cranking speed of 200 rpm and ambient temperature of 0°C show that advancing the intake valve close (IVC) timing increases the effective compression stroke that can improve the cylinder temperature by 5%. Further, implementing ‘extremely delayed IVO’ by retarding the timing from 1°CA to 61°CA aTDC could help to further increase the cylinder temperature by 14% compared to the base timings. The delayed opening of the intake valve leads to a higher expansion of the cylinder mass, leading to a lower cylinder pressure before IVO and a higher intake air velocity immediately after IVO. With the higher intake air velocity, the incoming air’s kinetic energy is dissipated to increase the stagnation temperature, resulting in an overall benefit in cylinder temperature. The experimental measurements conducted in a cold chamber with the optimized IVO and IVC timings confirmed the benefits by achieving a better cold-startability of the LCR engine. In comparison, the LCR engine with the stock valve timings could be started only up to +5°C, the optimized valve timings could ensure startability up to −10°C without any starting aids. Thus, the proposed approach of adopting the optimized valve timings can help LCR diesel engines to overcome the limitations of cold-startability.

Effects of Rate-Shaped and Multiple Injection Strategies on Pollutant Emissions, Combustion Noise and Fuel Consumption in a Low Compression Ratio Diesel Engine

An experimental investigation has been carried out to highlight the effects of different injection strategies on the performance and emissions of a low compression ratio Euro 5 diesel engine operated with high EGR rates. Rate-shaped main injections, achieved with piezoelectric and solenoid injectors by means of boot and injection fusion, respectively, as well as optimized multiple injection patterns have been compared. The results of the comparisons, performed with reference to a state-of-the-art double pilot-Main (pM) strategy, are presented in terms of engine-out exhaust emissions, combustion noise (CN) and fuel consumption. Rate-shaped main injections, when included in delayed multiple injection patterns, have shown a minor influence on reducing NOx, while a slight deterioration in soot has been found. Both a double pilot and a boot injection schedule have been able to reduce CN at low loads. A higher reduction in CN has been obtained with an injection fusion event. Finally, DoE optimized triple and quadruple injection strategies have led to improved soot-NOx trade-offs, with respect to the pM calibration. In fact, splitting the injection helps to entrain air inside the fuel plumes, thus creating locally leaner mixture (less prone to forming soot) and allowing increasing the EGR rates (reducing NOx formation).

Study on cold starting performance of a low compression ratio diesel engine by using intake flame preheating

Power density improvement is one the main techniques for engine thermal efficiency promotion. For turbocharged Diesel engine, low compression ratio in normally adopted for safety consideration under high power density operation. However, low compression ratio tends to lead cold starting problem. In this study, the influences factors and performances of a 10-cylinder turbocharged Diesel engine was investigated. An intake flame preheating model was built and validated by series of bench tests. The optimization of starting parameters and flame heating was conducted eventually. Based on the study, the basic performance flame pre-heating system under different conditions was disclosed. The cold starting boundary parameters of the Diesel engine was found. Moreover, the best starting fuel injection parameters were acquired. The research is beneficial for Diesel engine power density promotion based on cold starting ability

A novel method to improve the cold starting ability of a low compression ratio diesel engine through recompression of the charge

Reducing the compression ratio in a diesel engine will result in lower NOx and soot emissions but will lead to problem of starting and combustion instability at cold conditions. In this work, a novel method for improving cold starting ability has been conceptualized and verified through simulations and experiments. In this method, the temperature of the charge is enhanced by ejecting the hot air into the intake manifold at the end of compression stroke. Due to the irreversibility associated with this process, the temperature of the air in the intake manifold increases and this air is again inducted into the cylinder and compressed to further augment the temperature. This cycle is repeated till the temperature at the end of compression is sufficient to autoignite the injected fuel to aid first firing. This methodology was demonstrated on a single cylinder common rail diesel engine with a compression ratio of 14:1, which indicated that the temperature in the intake manifold progressively increased by up to 75 K within 10 crank shaft rotations during cranking. In subsequent experiments with the proposed system, ignition occurred right from the second rotation, whereas there is no combustion occurred in the conventional engine at ambient conditions (28°C). However, at cold condition (10°C), partial combustion was initiated only after 15 recompression rotations and does not produce any positive work output. To mitigate this, the injection schedule was further modified such that the partially burned products were retained in the cylinder without opening the valves and recompressed which autoignited the residual fuel during the subsequent compression stroke. At the end of this compression stroke, the in-cylinder temperature and pressure were high enough and hence the fuel was again injected which resulted in sustained combustion and produced an indicated mean effective pressure (IMEP) of 6 bar that could result in starting even at cold conditions (10°C). Hence, it was demonstrated that the proposed methodology with modified valve timing and injection scheduling has the potential to start the engine at low temperatures particularly with low compression ratios.

Boot injection dynamics and parametrical analysis of boot shaped injections in low-temperature combustion diesel engines for the optimization of pollutant emissions and combustion noise

Innovative direct-acting piezoelectric injectors that are capable of flexible injection rate shaping have been tested at a hydraulic test rig. The effect of boot injection dynamics on the injector hydraulic performance was analyzed on the basis of the measured injected flow-rate time histories. The injectors were then installed on a Euro 5 low-compression ratio diesel engine, fueled with conventional diesel oil and managed with a late PCCI type combustion. The engine has been tested at a dynamometer cell, and a parametric analysis has been performed considering both the charging time and the holding time of the boot injection in order to assess the impact of their variations on engine-out emissions, combustion noise and brake specific fuel consumption. Explanations of the cause-and-effect relationships between the boot injection parameters and the engine performance have been provided: a three-zone combustion diagnostic tool has been applied to support the experimental investigation.The tests at the engine dynamometer cell refer to the low-to-medium load and speed area of the engine NEDC zone, since the tests were focused on the exploitation of the boot injection in late PCCI combustion strategies.

Effects of Rail Pressure, Pilot Scheduling and EGR Rate on Combustion and Emissions in Conventional and PCCI Diesel Engines

In Diesel engines the optimization of engine-out emissions, combustion noise and fuel consumption requires the experimental investigation of the effects of different injection strategies as well as of a large number of engine operating variables, such as scheduling of pilot and after pulses, rail pressure, EGR rate and swirl level. Due to the high number of testing conditions involved full factorial approaches are not viable, whereas Design of Experiment techniques have demonstrated to be a valid methodology. However, the results obtained with such techniques require a subsequent critical analysis, so as to investigate the cause and effect relationships between the set of engine operating variables and the combustion process characteristics that affect pollutant formation, noise of combustion and engine efficiency. To this purpose, the zero-dimensional multizone diagnostic combustion model developed at ICEAL was applied for the combustion and emission formation analysis in two different diesel engines, for various sets of injection strategies and engine operating parameters. The experimental data were acquired at the highly dynamic test rig of ICEAL, both in a EURO V low compression ratio diesel engine with a twin-stage turbocharger, equipped with piezoelectric injectors, and in a PCCI low compression ratio diesel engine equipped with solenoid injectors. The model results were discussed and reported in the well known ϕ-T diagrams, which give a synthetic representation of the local thermodynamic charge conditions during the mixture formation and premixed diffusion combustion processes. The rail pressure increase was found to be an effective means to improve fuel-charge premixing and to lower the average local equivalence ratio of the charge during premixed combustion, so leading to a decrease in soot formation. As regards the effects of cooled high-pressure EGR on combustion, it was shown that an increase of its rate does not significantly affect the average equivalence ratio during premixed combustion, which is associated to the soot formation rate. Finally, a proper calibration of the dwell-time between pilot and main injection, so as to have the main injection pulse center-of-gravity phased in correspondence to the start of pilot burning, resulted to produce a reduction of CO and soot emissions higher than 50% with respect to baseline case, without any deterioration of NOx emissions

Analysis of Combustion Process in Cold Operation with a Low Compression Ratio Diesel Engine

Analysis of Combustion Process in Cold Operation with a Low Compression Ratio Diesel Engine

Cold Operation with Optical and Numerical Investigations on a Low Compression Ratio Diesel Engine

Cold Operation with Optical and Numerical Investigations on a Low Compression Ratio Diesel Engine

Characteristics of Unburned Hydrocarbons in a Low Compression Ratio Diesel Engine (Characteristics under Transient Operation and Reduction with Low Distillation Temperature Fuels)

In a DI diesel engine, reducing the compression ratio is effective to reduce smoke emissions without deterioration of NOx and thermal efficiency. However, with lower compression ratios, a low coolant temperature, or during the transient state, THC emissions significantly increase when using ordinary diesel fuel. The THC emissions during increasing loads significantly increased to very high concentrations from just after the start of the load increase until around the 10th cycle, rapidly decreased until the 20th cycle, and then gradually decreased to a steady state value after 1000 cycles. The dominant components present in the THC transient spike were lower hydrocarbons with carbon numbers around or below eight. In particular, ethylene showed a much higher concentration than the other components. In fully-warmed steady state operation with a compression ratio of 16 and diesel fuel, THC is reasonably low, but THC increases with lower coolant temperature or during the transient period just after increasing the load. This problem can be eliminated with a low distillation temperature fuel such as normal heptane. Benzene, butadiene, and other unregulated harmful emissions also increase under the high THC conditions with diesel fuel.

A Study on Low Compression Ratio Diesel Engine : 5th Report, Effects of Intake Air Temperature to Burning Rate and Engine Perbormances

A Study on Low Compression Ratio Diesel Engine : 5th Report, Effects of Intake Air Temperature to Burning Rate and Engine Perbormances

Studies on Low Compression Ratio Diesel Engine : 4th Report, Effects of Auxiliary Injection

In order to realize a low compression ratio diesel engine, the problematic points, for example the engine noise resulting from the maximum rate of pressure rise and exhaust emission (NOx), have to be improved. In this paper, the auxiliary fuel injection was tried using a direct injection type engine for improving the problematic points stated above, and further some factors which affected the effects of the auxiliary fuel injection, for instance the combustion chamber configuration and the compression ratio, were discussed. As a result of our experiments, the auxiliary fuel injection in a low compression ratio engine was found a favorable means of suppressing the emission of noise and NOx, and in this case the optimum timing of auxiliary fuel injection was near the top dead center of exhaust stroke, i.e. Vigom injection, with respect to specific fuel consumption and noise emission. On the effects of auxiliary fuel injection, especially with respect to improving the maximum rate of pressure rise, the extent of the effects of auxiliary fuel injection was intensive, as the injection rate of the main injection was large and the turbulence in combustion chamber was strong. Besides, on the relationships between the compression ratio and the effects of auxiliary fuel injection, the efects of auxiliary fuel injection were intensitve at lower compression ratio with respect to the maximum rate of pressure rise and noise emission. Consequently, the adoption of auxiliary fuel injection in a low compression ratio engine might be very effective.

Studies on Low Compression Ratio Diesel Engine : 4th Report, The Effects of the Auxiliary Injection

Studies on Low Compression Ratio Diesel Engine : 4th Report, The Effects of the Auxiliary Injection

Studies on Low Compression Ratio Diesel Engine : 3rd Report, Relation between Combustibility and Performances

In a diesel engine, by a systematic controlling of the burning rate, the performances i.e., thermal efficiency, maximum pressure, maximum rate of pressure rise, combustion noise emission and maximum combustion temperature which affects the density of NOx emission, etc. may be controlled. In this paper, the performance values, for example the indicated thermal efficiency, were calculated stepwise based on Wiebe's combustion function, and the relationships between the combustion rate and each performance value were investigated. In addition, the harmonics of engine noise were considered to be related to that of the cylinder pressure variation, hence the harmonics of cylinder puressure variation were calculated for the estimation of noise emission. As a result of the calculations, it was clarified that when the combustion rate was controlled to a desired free value with a low compression ratio, the performances, i.e. indicated thermal efficiency, maximum pressure, combustion noise etc., could be improve simultaneously. Thus, a theoretical guide to improving the performances of a low compression ratio diesel engine was obtained.

A Study on Low Compression Ratio Diesel Engine : 2nd Report, Effects of Combustion Chamber Configuration in Direct Injection Type Engine

A Study on Low Compression Ratio Diesel Engine : 2nd Report, Effects of Combustion Chamber Configuration in Direct Injection Type Engine

Studies on the Low Compression Ratio Diesel Engine : 1st Report, The Problems Arising from Low Compression Ratio

Up to this time, the higher compression rations have been widely used in high speed diesel engines, but a lower compression ratio is demanded to achieve an increase in output with special regard to the stress of structure, engine noise etc. In this paper, some problems arising from the reduction of compression ratio in diesel engine were first described, and the basic data required to derive a low compression ratio in diesel engine were first described, and the periments, it was shown that the most important problems with low compression ratio are the reduction of maximum output and the increase of specific fuel consumption and this depends rather on the increase of cooling loss than on the reduction of theoretical thermal efficiency considering the rate of heat release in cycle. In the engine noise, the lower frequency part of sound pressure was reduced while, on the other hand the higher frequency part increased at a lower compression ratio. Consequently the sound pressure level of the overall range increased. In addition, the higher frequency part seems to be affected by the maximum rate of pressure rise regardless of compression ratio.

Studies on Low Compression Ratio Diesel Engine : 3rd Report, Relationships between Engine Performances and Combustibility

Studies on Low Compression Ratio Diesel Engine : 3rd Report, Relationships between Engine Performances and Combustibility

A Study on the Low Compression Ratio Diesel Engine : 1st Report, The Problems Arising from Low Compression Ratio

A Study on the Low Compression Ratio Diesel Engine : 1st Report, The Problems Arising from Low Compression Ratio