Abstract
Research and/or Engineering Questions/Objective
One of the key issues facing the low compression ratio engine is in the starting difficulty, especially in harsh environments (low temperature, high altitude). Experimental study on heating coolant temperature to improve start performance of diesel engine(compression ratio14.25) under variable altitude environment (0m, 3000m, 4500m), And different coolant temperatures influence on combustion characteristics of starting process.
Methodology
The engine intake and exhaust pressure was controlled by the Imtech Germany's system to stimulate the altitude conditions including 0 m、3000m、4500 m, the system control range is 57.6 kPa ~ 101.3 kPa, accuracy±0.5 kPa. The speed、combustion pressure and after intercooling pressure data of starting process of a compression 14.25 two-stage turbocharging intercooling diesel engine were collected through high precision water-cooled cylinder pressure sensor, an intake pressure wave sensor and a Hall effect speed sensor with the sampling frequency of 0.1°CA
Results
Coolant temperature rised every 20 ℃, Speed up period of starting reduced by an average of 2.9%, 14.83%, 48.52% in the altitude of 0m, 3000m, 4500m. The main patterns of starting combustion of different coolant temperatures were twin peaks and single parent peak under plain condition (0 m) with stronger combustion stability and the better acting ability. Speed up period shortened, Indicated Mean Effective Pressure increased, the ratio of the twin peaks cycle decreased and the single parent peak cycle increased with the increase of the coolant temperature. The cycle of afterburning and missing of fire in starting disappeared, the ratio of the twin peaks cycle decreased and the single parent peak cycle increased, Indicated Mean Effective Pressure increased under the plateau condition (altitude of 3000m and 4500m) , with the increase of the coolant temperature. Coolant temperature rised every 20 ℃, the ratio of the single parent peak cycle of Speed up period of starting increased by an average of 11.87%、17.07%、35.91% in the altitude 0m, 3000m, 4500m and Indicated Mean Effective Pressure increased by an average of 0.35%，111.86%、243.87%. About the combustion characteristics of idle period ,coolant temperature rised every 20 ℃,the highest explosion pressure phase advanced by an average of2.14°CA 、3.85°CA 、4.5°CA, combustion duration shortened 4.79%、6.06%、7.38% in the altitude of 0m, 3000m, 4500m.
Limitations of this study
An important limitation of the current study was some errors between the simulation condition that simulate the diesel engine in different altitude through the intake and exhaust pressure control in test chamber and the actual altitude environment.
What does the paper offer is new in the field including comparison with others’ work by the authors?
There is no report about the effect of coolant temperature on the starting process of low compression ratio diesel engine under variable altitude conditions, the Author has studied the effect of coolant temperature on the performance and combustion characteristics of low compression diesel engine under variable altitude conditions through experiments to explore the solution to the low compression ratio diesel engine starting difficulty on plateau.
Conclusions
The effect of coolant temperature on the starting process performance and combustion characteristics of low compression diesel engine was more significant with the altitude increasing .In the altitude of 4500m, coolant temperature rised every 20 ℃, Speed up period of starting reduced by an average of 48.52%, the ratio of the single parent peak cycle increased by an average of 35.91%, Indicated Mean Effective Pressure increased by an average of 243.87%, the highest explosion pressure phase advanced by an average of 4.5°CA, the combustion duration shortened 7.38% in idle period.
Key Words : Diesel engine; Low compression ratio; Coolant temperature; Variable altitude; Starting; Combustion characteristics