A Ramesh

Homogeneous charge compression ignition (HCCI) engines have the potential to operate with low nitric oxide (NOx) and soot emissions. Diesel HCCI engines pose challenges related to too early combustion, high combustion rates and wall wetting of the fuel. Injecting diesel in pulses has been shown to improve combustion in these engines. In this work, diesel injected in five timed pulses has been investigated in a compression ignition (CI) engine operating in HCCI mode. The influence of varying the first, middle and last injection pulse durations alone, in sequence, while maintaining all the other injection pulse durations equal has been studied. In addition, the influence of the injection timing of the last injection pulse was also studied. A comparison of the results has been made with HCCI operation using diesel injection in a single pulse at an injection timing of 100° CA before top dead centre (TDC) and also with the conventional compression ignition mode of operation under similar outputs. The results show that, multiple pulse (MP) injection is better than injecting the fuel in a single pulse (SP) as it leads to lower emissions and higher thermal efficiency. This is because of better combustion phasing and higher heat release rates.

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.

Low compression ratio (LCR) approach in diesel engines can reduce the oxides of nitrogen (NOx) and soot emissions simultaneously owing to lower temperatures and longer fuel-air premixing time. The present work investigates the effects of lowering the geometric compression ratio (CR) from 18:1 to 14:1 in a naturally aspirated (NA) single cylinder common rail direct injection (CRDI) diesel engine. Based on the investigations done across the entire speed and load range, significant benefits were observed in the NOx and soot emissions. However, lowering the compression ratio had adverse effects on brake specific fuel consumption (BSFC), unburned hydrocarbon (HC) and carbon monoxide (CO) emissions, especially at low-load and high-speed operating points. To overcome these limitations, novel strategies including split-cooling system (SCS) and secondary exhaust valve opening (SEVO) are proposed in the present work. While the fuel injection parameters optimization specific to LCR could help to improve the BSFC, HC and CO emissions penalty to a reasonable extent, the SCS concept can provide further benefits by reducing the heat loss to coolant and improving the engine component temperatures. Increasing the residual gas fraction using the optimized SEVO concept could further improve the charge temperature leading to a further reduction in the BSFC, HC and CO emissions. The net benefits of the optimized LCR approach are quantified for the modified Indian drive cycle (MIDC) using a one-dimensional simulation tool. The results obtained show a signification reduction of 22% and 74% in NOx and soot emissions respectively as compared to the base 18 CR engine results. Moreover, the penalty in HC and CO emissions could be contained to a large extent resulting in only a slight penalty of 23% and 20% respectively. Furthermore, the higher BSFC with the LCR approach could be successfully addressed and the final values were found to be better than the stock compression ratio by 1.5%. Overall, the strategies proposed in the present work are found to be beneficial to develop modern diesel engines in compliance with the future emission regulations which demand extreme control on NOx and soot emissions.

Different methods to improve the performance of a jatropha oil based compression ignition engine were tried and compared. A single cylinder water-cooled, direct injection diesel engine was used. Base data were generated with diesel and neat jatropha oil. Subsequently, jatropha oil was converted into its methyl ester by transesterification. Jatropha oil was also blended with methanol and orange oil in different proportions and tested. Further, the engine was modified to work in the dual fuel mode with methanol, orange oil, and hydrogen being used as the inducted fuels and the jatropha oil being used as the pilot fuel. Finally, experiments were conducted using additives containing oxygen, like dimethyl carbonate and diethyl ether. Neat jatropha oil resulted in slightly reduced thermal efficiency and higher emissions. Brake thermal efficiency was 27.3% with neat jatropha oil and 30.3% with diesel. Performance and emissions were considerably improved with the methyl ester of jatropha oil. Dual fuel operation with methanol, orange oil, and hydrogen induction and jatropha oil injection also showed higher brake thermal efficiency. Smoke was significantly reduced from 4.4 BSU with neat jatropha oil to 2.6 BSU with methanol induction. Methanol and orange oil induction reduced the NO emission and increased HC and CO emissions. With hydrogen induction, hydrocarbon and carbon monoxide emissions were significantly reduced. The heat release curve showed higher premixed rate of combustion with all the inducted fuels mainly at high power outputs. Addition of oxygenates like diethyl ether and dimethyl carbonate in different proportions to jatropha oil also improved the performance of the engine. It is concluded that dual fuel operation with jatropha oil as the main injected fuel and methanol, orange oil, and hydrogen as inducted fuels can be a good method to use jatropha oil efficiently in an engine that normally operates at high power outputs. Methyl ester of jatropha oil can lead to good performance at part loads with acceptable levels of performance at high loads also. Orange oil and methanol can be also blended with jatropha oil to improve viscosity of jatropha oil. These produce acceptable levels of performance at all outputs. Blending small quantity of diethyl ether and dimethyl carbonate with jatropha oil will enhance the performance. Diethyl ether seems to be the better of the two. Copyright © 2010 by ASME.

Modelling of a turbocharger is of interest to the engine designer as the work developed by the turbine can be used to drive a compressor coupled to it. This positively influences charge air density and engine power to weight ratio. Variable geometry turbocharger (VGT) additionally has a controllable nozzle ring which is normally electropneumatically actuated. This additional degree of freedom offers efficient matching of the effective turbine area for a wide range of engine mass flow rates. Closing of the nozzle ring (vanes tangential to rotor) result in more turbine work and deliver higher boost pressure but it also increases the back pressure on the engine induced by reduced turbine effective area. This adversely affects the net engine torque as the pumping work required increases. Hence, the optimum vane position for a given engine operating point is to be found through simulations or experimentation. A thermodynamic simulation model of a 2.2l 4 cylinder diesel engine was developed for investigation of different control strategies. Model features map based performance prediction of the VGT. Performance of the engine was simulated for steady state operation and validated with experimentation. The results of the parametric study of VGT's vane position on the engine performance are discussed.

In this work various methods of using vegetable oil (Jatropha oil) and methanol such as blending, transesterification and dual fuel operation were studied experimentally. A single cylinder direct injection diesel engine was used for this work. Tests were done at constant speed of 1500 rev min-1 at varying power outputs. In dual fuel operation the methanol to Jatropha oil ratio was maintained at 3:7 on the volume basis. This is close to the fraction of methanol used to prepare the ester with Jatropha oil. Brake thermal efficiency was better in the dual fuel operation and with the methyl ester of Jatropha oil as compared to the blend. It increased form 27.4% with neat Jatropha oil to a maximum of 29% with the methyl ester and 28.7% in the dual fuel operation. Smoke was reduced with all methods compared to neat vegetable oil operation. The values of smoke emission are 4.4 Bosch Smoke Units (BSU) with neat Jatropha oil, 4.1 BSU with the blend, 4 BSU with methyl ester of Jatropha oil and 3.5 BSU in the dual fuel operation. The Nitric Oxide (NO) level was lower with Jatropha oil compared to diesel. It was further reduced in dual fuel operation and the blend with methanol. Dual fuel operation showed higher hydrocarbon (HC) and carbon monoxide (CO) emissions than the ester and the blend. Ignition delay was higher with neat Jatropha oil. It increased further with the blend and in dual fuel operation. It was reduced with the ester. Peak pressure and rate of pressure rise were higher with all the methods compared to neat Jatropha oil operation. Jatropha oil and methyl ester showed higher diffusion combustion compared to standard diesel operation. However, dual fuel operation resulted in higher premixed combustion. On the whole it is concluded that transesterification of vegetable oils and methanol induction can significantly enhance the performance of a vegetable oil fuelled diesel engine. © 2003 Elsevier Ltd. All rights reserved.

The present work proposes a viable approach to develop single-cylinder diesel engines for the future by implementing regulated intake air boosting (RIAB) and engine downspeeding (ED) along with the well-established low compression ratio (LCR) approach. The investigations were conducted in a mass-production light-duty single-cylinder diesel engine initially equipped with a naturally aspirated (NA) intake system. By lowering the compression ratio (CR) and implementing the intake air boosting (IAB) using a belt-driven supercharger, the maximum brake mean effective pressure (BMEP) of the engine could be increased by 50%. More importantly, the improved performance could be achieved without violating the peak firing pressure (PFP) limits. However, a significant penalty was observed in the brake-specific fuel consumption (BSFC) at low-load operating points due to the additional power consumption of the IAB system. Hence, RIAB was implemented to optimize the boost pressure with respect to engine load to simultaneously reduce the BSFC and oxides of nitrogen (NOx) and soot emissions. Further, the increased full-load performance of the engine was leveraged to implement the ED approach that could reduce the operating speeds of the engine by 37.8%. It was observed that the benefits of downspeeding a supercharged engine are significantly high due to the simultaneous reduction of the frictional losses of the base engine and the power consumption of the supercharger. Overall, by combining the above concepts and the proven LCR approach, significant benefits could be achieved in fuel economy and exhaust emissions that are quantified for the regulatory Modified Indian Drive Cycle (MIDC) using a one-dimensional tool. The obtained results show a net reduction of 77.8% and 39.5% in the soot and NOx emissions, respectively. Moreover, a significant benefit of 14.8% could be achieved in the fuel economy. Thus the proposed approach can be used to develop single-cylinder diesel engines for the future to improve vehicle performance and comply with stringent emission regulations.

In the present work, the benefits of the low compression ratio (LCR) concept on simultaneous reduction of oxides of nitrogen (NOx) and soot emissions could be further enhanced by optimizing the piston bowl design using a 3-dimensional computational fluid dynamics (CFD) tool. A single-cylinder, direct-injection diesel engine was used for the present investigations. In its mass-production version, the engine had a compression ratio (CR) of 18:1 that was considered as the stock CR from which the LCR variants were derived. The initial and unoptimized piston design of the LCR variant with CR of 14:1 was arrived at using an offset bowl geometry from the stock compression ratio variant, and the corresponding benefits were quantified. The NO (nitric oxide) and soot reduction potential of the LCR variant could be further enhanced by adopting a step-by-step optimization procedure focused on the principal parameters of the bowl viz., piston bowl diameter, centre pip depth, reentrancy and bottom profile. Based on numerical investigations, an optimal piston bowl design could be arrived at that can significantly enhance the benefits of the LCR approach on NO and soot emissions. At a reference operating point of 2000 rpm and 40 N-m, by adopting the optimized profile, the NO reduction potential of the LCR variant could be improved from 10.3% to 40.2%. Moreover, the soot reduction potential could also be improved from 79.1% to 84.2%. The benefits of the optimized bowl design were also confirmed by engine dynamometer measurements across the engine’s operating speed range. Thus, it can be concluded that optimization of the piston bowl design specific to the LCR variant could enhance the NOx and soot emission benefits that can help diesel engines comply with the stringent emission regulations.