







































Gharehghani and Andwari/Future Technology                                                                      August 2022| Volume 01 | Issue 02 | Pages 34-35 

34 
 

 

News & Views 

Towards fossil-free fuels in sustainable 

powertrain; alcohol-fueled low-temperature 

combustion (LTC) 
Ayat Gharehghani1*, Amin Mahmoudzadeh Andwari2 

Low-temperature combustion (LTC) engines are able to reduce nitrogen oxides (NOx) and particulate matter (PM) emissions, 

simultaneously. LTC engines suffer from higher amounts of unburned hydrocarbon (uHC) and carbon monoxide (CO) 

emissions, particularly in low-load operating conditions of the engine. The existence of oxygen molecules in the alcohol fuels 

not only results in more combustion completeness but also leads to lower CO and uHC emissions.

TC strategies in internal 
combustion engines provide 
lower emissions besides high 

engine performance according to 
chemically controlled combustion 
temperature. These strategies are 
divided into three engine types which 
are premixed charge compression 
ignition (PCCI), homogenous charge 
compression ignition (HCCI), and 
reactivity control compression ignition 
(RCCI) engines [1]. The main purpose 
of LTC is to provide a lean homogenous 
air-fuel mixture to obtain lower 
emissions along with appropriate 
engine power output. Various fuel 
supply strategies together with 
different fuel types are applied in LTC, 
including low reactivity fuels (LRF) 
(e.g., gasoline and alcohols) and high 
reactivity fuels (HRF) (e.g., diesel, 
dimethyl ether etc.) [2]. A combination 
of LRF and HRF has been used in LTC 
strategies. Alcohol fuels have been 
more of interest among other types of 
LRFs for LTC engine application in 
several studies. Ethanol, methanol, 
butanol, and n-butanol are four types 
of these fuels used as LRFs in LTC 
engines [3,4]. These fuels are usually 
employed with HRFs like diesel (n-
heptane in numerical study) or due to 
cooling effects employed at high engine 
loads as single fuels. Owing to their 
diverse chemical and physical 
properties, the alcohol fuels can affect 
differently on the engine combustion 
and emission characteristics [5]. The 
relationship between different 
pollutants for different values of local 
equivalence ratio and temperature in 
the combustion strategies of 
conventional diesel combustion (CDC), 
HCCI, PCCI, and RCCI is shown in 
Figure 1. Although the boundaries 

shown in Figure 1 are slightly non-
marginal, the form is useful for 
understanding the different 
combustion properties [1]. According 
to Figure 1, CDC comprises areas with 
high local equivalence ratios and high 
local temperatures, but LTC strategies 
tend to operate in poor equivalence 
ratios with lower maximum 
temperatures than the formation of 
nitrogen oxides (NOx) and soot 
emissions prevented. However, LTC 
zones are those where the least 
oxidation of unburned hydrocarbons 
and carbon monoxide occurs. Although 
LTC strategies can reduce the 
emissions of NOx and soot while 
maintaining diesel cycle performance 
with higher efficiencies, they regularly 
increase the emissions of uHCs, CO 
together with lower combustion 
controllability. These strategies also 
increase the maximum pressure rise 
rate (PPRR) of the combustion [2]. 
Methanol, ethanol, and butanol are the 
most utilized alcohol-based fuels in 
both spark ignition (SI) cycle and 
compression ignition (CI) cycle engine 
applications. The chemical structure of 
alcohol is represented as CnH2n+1OH. 
The higher-octane number of alcohols 
can reduce the knocking tendency in SI 
engines, whereas the presence of fuel 
oxygen content in alcohol diesel blends 
lowers the soot formation tendency in 
compression ignition engines. 
Concomitantly, blending alcohol 
results in lower emissions in both the 
SI and CI version of ICEs [6]. Since the 
LTC strategy improves fuel 
atomization and mixing, it not only 
lowers the local equivalence ratio but 
also reduces combustion temperature 
[7,8], which can abate the NOx and 

particulate matter (PM) emissions 
simultaneously [9,10].  

 
Figure 1. Temperature and equivalence  
ratio changes in operational regimes of 

CDC, HCCI, PCCI, and RCCI [1] 

The alcohol fuels take advantage of the 
full merits of HCCI combustion due to 
their desirable properties such as 
higher-octane number, a wider range 
of equivalence ratios together with 
emissions reduction [7]. The alcohol 
fuel used in another mode of LTC, such 
as the RCCI engine, increases the 
thermal efficiency along with 
decreasing harmful exhaust pollutants 
[9]. CO and HC emissions are the main 
concerns in LTC strategies which are 
the result of incomplete combustion of 
fuel (misfire) in the engine [8]. CO 
emission is strongly dependent on the 
combustion temperature of the 
homogeneous lean mixtures, and as a 
result, in ultra-lean mixtures, the 
temperature becomes too cold for 
completion of the oxidation reactions 
and causes a high level of CO in HCCI 
combustion. The variation of CO 
emissions for natural gas, ethanol, and 
methanol fuels in HCCI combustion is 
illustrated in Figure 2. It can be 

 

 
Open Access Journal https://doi.org/10.55670/fpll.futech.1.2.4 

 

 

 

 

August 2022| Volume 01 | Issue 02 | Pages 34-35 

Future Technology Journal homepage: https://fupubco.com/futech 

 

ISSN 2832-0379 

https://doi.org/10.55670/fpll.futech.1.2.4
https://fupubco.com/futech


Gharehghani and Andwari/Future Technology                                                                      August 2022| Volume 01 | Issue 02 | Pages 34-35 

35 
 

perceived from Figure 2 that the CO 
emission level in the natural gas-fueled 
case is high above the two other fuels, 
and for all fuel equivalence ratios and 
intake temperatures, its value is higher 
than the limits of the Euro 6 pollution 
regulations, which is under 1.5 gr/kWh 
[10]. But as shown in Figure 2, for 
ethanol and methanol-fueled cases, it is 
possible to define the operating region 
based on Euro 6 pollution regulations 
for CO emission. As mentioned, the 
presence of fuel oxygen content in 
alcohol fuels resulted in complete 
combustion leading to lower CO and 
uHC emissions. 
 
 
 
 
 
 
 
 
 

  
 
 
 
 
 
 

 
 
 
 
 
 
 

Reference 
[1]  A. K. Agarwal, Akhilendra 

Pratap Singh, Rakesh Kumar 
Maurya, Evolution, challenges 
and path forward for low 
temperature combustion 
engines, Progress in Energy 
and Combustion Science, 
Volume 61, 2017, Pages 1-56, 
ISSN 0360-1285, 
https://doi.org/10.1016/j.pecs
.2017.02.001.  

[2]  A. M. Andwari, A. Pesiridis, V. 
Esfahanian, M. F. Muhamad 
Said. “Combustion and 
Emission Enhancement of a 
Spark Ignition Two-Stroke 
Cycle Engine Utilizing Internal 
and External Exhaust Gas 
Recirculation Approach at 
Low-Load Operation”, 
Energies, 2019, 12 (4), 609; 
doi:10.3390/en12040609 

[3]  Andwari, A.M.; Said, M.F.M.; 
Aziz, A.A.; Esfahanian, V.; 
Salavati-Zadeh, A.; Idris, M.A.; 
Perang, M.R.M.; Jamil, H.M. 
Design, Modeling and 
Simulation of a High-Pressure 
Gasoline Direct Injection (GDI) 
Pump for Small Engine 
Applications. J. Mech. Eng. 
2018, 1, 107–120 

 
 

[4]  A. M. Andwari, Azhar Abdul 
Aziz, M .F. Muhamad Said and 
Z. A. Latiff, A. Ghanaati. 
“Influence of Hot Burned Gas 
Utilization on The Exhaust 
Emission Characteristics of A 
Controlled Auto-Ignition Two-
Stroke Cycle Engine”, 
International Journal of 
Automotive and Mechanical 
Eng., Vol 11 (2015), pp 2396-
2404, 
DOI:http://dx.doi.org/10.1528
2/ijame.11.2015.20.0201 

[5]  J. Moradi, A. Gharehghani, M. 
Aghahasani. Application of 
machine learning to optimize 
the combustion characteristics 
of RCCI engine over wide load 
range. Fuel 324, Part A, 2022, 
124494.  
https://doi.org/10.1016/j.fuel.
2022.124494  

[6]  A. Gharehghani, HR. Abbasi, P. 
Alizadeh. Application of 
machine learning tools for 
constrained multi-objective 
optimization of an HCCI engine. 
Energy, 233, 2021,121106. 
https://doi.org/10.1016/j.ener
gy.2021.121106  

[7]  J. Moradi, A. Gharehghani, M. 
Mirsalim. Numerical 
investigation on the effect of 
oxygen in combustion 

characteristics and to extend 
low load operating range of a 
natural-gas HCCI engine. 
Applied Energy, 276, 
2020,115516.  
https://doi.org/10.1016/j.ape
nergy.2020.115516  

[8]  MM. Salahi, A. Gharehghani. 
Control of combustion phasing 
and operating range extension 
of natural gas PCCI engines 
using ozone species. Energy 
Conversion and Management, 
199, 2019,112000. 
https://doi.org/10.1016/j.enco
nman.2019.112000.  

[9]  A. Gharehghani. Load limits of 
an HCCI engine fueled with 
natural gas, ethanol, and 
methanol. Fuel, 239, 
2019,1001-1014.  
https://doi.org/10.1016/j.fuel.
2018.11.066  

[10]  A. Kakoee, A. Gharehghani, 
Comparative study of hydrogen 
addition effects on the natural-
gas/diesel and natural-
gas/dimethyl-ether reactivity 
controlled compression 
ignition mode of operation. 
Energy Conversion and 
Management, 196, 2019, 92-
104. 
https://doi.org/10.1016/j.enco
nman.2019.05.113  

 

1*Ayat Gharehghani 

School of Mechanical Engineering, 

Iran University of Science and 

Technology, Tehran, Iran 

Ayat_Gharehghani@iust.ac.ir 

2Amin Mahmoudzadeh Andwari 

Machine and Vehicle Design 

(MVD), Materials and Mechanical 

Engineering, University of Oulu, 

P.O. Box 4200, FI-90014 Oulu, 

Finland 

 

 

Figure 2. Operating range of HCCI engine based on CO emission for various fuel [7] 

 This article is an open-access article 

distributed under the terms and conditions of the Creative 

Commons Attribution (CC BY) license 

(https://creativecommons.org/licenses/by/4.0/). 

mailto:Ayat_Gharehghani@iust.ac.ir

